This page shows what was measured, who it was measured in, and what that does not settle.
What Levothyroxine does in the body
Used to replace thyroid hormone when the thyroid is underactive.
Levothyroxine is the same molecule your thyroid makes. Once absorbed, tissues convert it into the more active form, which enters the cell nucleus, binds a receptor sitting on DNA, and switches metabolic genes on. It is not a stimulant and it does not add anything: it replaces what a gland is not producing, and if the gland is producing enough already, there is nothing for it to replace.
What happened in people
It is effective replacement for clear thyroid-hormone deficiency.
✓ Reviewed first-read answer
Where this came from
A person wrote this and a reviewer approved it against this exact record. It carries no effect size.
A reviewer approved this against this record. The reviewed-claim record carrying the exact population and effect size does not exist yet.
No source is stored against this line.
The limit that matters most
In older people with only mildly abnormal tests, normalising the test did not improve symptoms or tiredness.
Where it acts
Cell nucleus, essentially every tissue in the body
Kind of result
The kind of result is not recorded
Supervision
RNAWiki has not recorded a supervision or regulatory status for this substance.
What the registries record it as
Its recorded molecular formula is C15H10I4NNaO4, weighing 798.85 g/mol.
US prescribing information · 4e9adc35-3aba-4a0d-9c4e-7e7ee2ffdabd · read 2026-08-30
Where each sentence above came from
No recorded sentence describes the change this makes in a way that stands on its own. The page opens with what it is taken for instead, and the recorded explanation follows below.
Shown as the opening line on this page.
The limit a reviewer approved as the one that matters most here.
The four opening statements run to 88 words.
Words this page uses
Four words worth knowing first
Chosen from what this page shows, with each one explained before the word it depends on.
Stand-in result
A stand-in result is a number measured because the real result takes too long.
A picture of it, and where the picture fails
It is like judging a journey by the speedometer rather than by arriving.
Where that stops being true. Speed does predict arrival. Many stand-in results do not predict the real one.
What people get wrong. A stand-in result is often reported as the result itself.
A surrogate endpoint substituted for a clinical endpoint, valid only where the substitution has been shown to hold.
Randomisation
Randomisation means chance decides who gets which treatment.
A picture of it, and where the picture fails
It is like a coin toss deciding the groups.
Where that stops being true. A coin toss is fair once. Fairness here comes from doing it for everyone.
What people get wrong. It is thought to make groups identical. It makes them similar on average, including on things nobody measured.
Allocation of participants to arms by a chance process, so that unmeasured factors are balanced in expectation.
Confidence interval
A confidence interval is the range the true answer is likely to sit in.
A picture of it, and where the picture fails
It is like a weather forecast giving a range rather than one number.
Where that stops being true. A forecast range covers tomorrow. This one covers what the study could resolve.
What people get wrong. The middle number is read as the answer. A range crossing zero means no change is still possible.
An interval estimate that would contain the true parameter in a stated proportion of repeated studies.
Formulation
A formulation is the exact made-up form a substance comes in.
A picture of it, and where the picture fails
It is like the difference between a whole bean and instant coffee.
Where that stops being true. Coffee tastes different. A formulation can change how much reaches the blood.
What people get wrong. Two products with the same name are assumed to behave the same. They often do not.
The specific composition and physical form of a product, including salt, excipients and release profile.
What happened in people◇Read from sources, not yet reviewed
What was measured, goal by goal
One row for each goal a registered study measured something for. One column for each kind of thing that could be measured.
Registered studies list 40 outcome measures that RNAWiki could read. A registered study says what someone planned to measure. It does not say what they found. 0 of the matched studies tested this substance, and 0 posted a result.
There is no single score. A strong test result and a weak life result are different facts.
Goals down the side, kinds of measurement across the top. Each cell says what kind of thing was registered, not what was found.
Goal
Life outcome
What a body can do
How a person feels
A test result
A step in the body
Harms
How long
Who was studied
Energy
∅Nothing in the sources checkedNo registered study lists a life outcome for this goal.
∅Nothing in the sources checkedNo registered study lists a performance measure for this goal.
∅Nothing in the sources checkedNo registered study lists a symptom measure for this goal.
∅Nothing in the sources checkedNo registered study lists a test result for this goal.
∅Nothing in the sources checkedNo registered study lists a body-step measure for this goal.
—Not recordedHarms were not a registered measure for this goal.
—Not recordedNo finished study window is recorded.
…Waiting for a reviewerWho was studied is listed further down the page.
Mood
∅Nothing in the sources checkedNo registered study lists a life outcome for this goal.
∅Nothing in the sources checkedNo registered study lists a performance measure for this goal.
…Waiting for a reviewer2 registered symptom measure.
∅Nothing in the sources checkedNo registered study lists a test result for this goal.
∅Nothing in the sources checkedNo registered study lists a body-step measure for this goal.
—Not recordedHarms were not a registered measure for this goal.
—Not recordedNo finished study window is recorded.
…Waiting for a reviewerWho was studied is listed further down the page.
Cholesterol
∅Nothing in the sources checkedNo registered study lists a life outcome for this goal.
∅Nothing in the sources checkedNo registered study lists a performance measure for this goal.
∅Nothing in the sources checkedNo registered study lists a symptom measure for this goal.
△Only a number moved1 registered test measure.
∅Nothing in the sources checkedNo registered study lists a body-step measure for this goal.
—Not recordedHarms were not a registered measure for this goal.
—Not recordedNo finished study window is recorded.
…Waiting for a reviewerWho was studied is listed further down the page.
Blood sugar
∅Nothing in the sources checkedNo registered study lists a life outcome for this goal.
∅Nothing in the sources checkedNo registered study lists a performance measure for this goal.
∅Nothing in the sources checkedNo registered study lists a symptom measure for this goal.
△Only a number moved1 registered test measure.
∅Nothing in the sources checkedNo registered study lists a body-step measure for this goal.
—Not recordedHarms were not a registered measure for this goal.
—Not recordedNo finished study window is recorded.
…Waiting for a reviewerWho was studied is listed further down the page.
Healthy ageing
…Waiting for a reviewer1 registered study measure of this kind. No reviewed result yet.
∅Nothing in the sources checkedNo registered study lists a performance measure for this goal.
∅Nothing in the sources checkedNo registered study lists a symptom measure for this goal.
∅Nothing in the sources checkedNo registered study lists a test result for this goal.
∅Nothing in the sources checkedNo registered study lists a body-step measure for this goal.
—Not recordedHarms were not a registered measure for this goal.
—Not recordedNo finished study window is recorded.
…Waiting for a reviewerWho was studied is listed further down the page.
Which registered measures put each goal on this table
Energy
resting energy expenditure; energy expenditure
Mood
hamilton rating scale for depression; beck depression inventory
Cholesterol
cholesterol; lipid profile
Blood sugar
insulin sensitivity
Healthy ageing
all cause mortality
Sorted by fixed word lists, version v1. A name the rules do not recognise stays unsorted rather than moving to the nearest column.
What each mark on this table means
∅ Nothing in the sources checked
No registered study lists a life outcome for this goal.
— Not recorded
Harms were not a registered measure for this goal.
… Waiting for a reviewer
Who was studied is listed further down the page.
△ Only a number moved
1 registered test measure.
What happened in people◇Read from sources, not yet reviewed
What happened in people
Each card is one study: the exact question it asked, who was in it, and whether it showed what it set out to show.
Change at 1 year in the ThyPRO Hypothyroid Symptoms score and Tiredness score in subclinical hypothyroidism
✗ The study did not show it
Who was studied
TRUST (NCT01660126)
How many people
737
Study design
Randomised double-blind placebo-controlled trial, 1 year
Compared against
A dummy treatment
Kind of result
A number that stands in for health
What was found
Between-group differences 0.0 (95% CI -2.0 to 2.1) and 0.4 (-2.1 to 2.9) against a 9-point minimum clinically important difference
Repeated elsewhere
Replicated
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. The surrogate responded exactly as intended: thyrotropin fell from 6.40 to 3.63 mIU/L. Only the symptoms did not.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet in twelve strengths, plus soft-gel capsules, an oral solution and an intravenous formulation for myxoedema coma
Interval reported. 95% CI -2
Written into the record, not signed off as a reviewed claim.
Prospectively planned combined analysis of two randomised trials, 1 year
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
Adjusted differences 1.3 (95% CI -2.7 to 5.2), P = 0.53 and -0.1 (-4.5 to 4.3), P = 0.96
Repeated elsewhere
Replicated
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. 84% completed. Adverse events occurred in 29.5% on levothyroxine and 28.8% on placebo, so the absence of benefit was not offset by an absence of risk.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet in twelve strengths, plus soft-gel capsules, an oral solution and an intravenous formulation for myxoedema coma
Interval reported. 95% CI -2
Written into the record, not signed off as a reviewed claim.
RNAWiki holds 4 written-up human studies for this substance, each with the question it asked.
How we know it
Each card names the study, the number of people and what the study set out to measure.
What this does not prove
These summaries were written by a person and have not been signed off as reviewed claims.
Why it matters
A study that failed is as informative as one that worked, and both are here.
What we still do not know
No reviewed claim exists, so no exact population, effect size or interval is published yet.
What happened in people◇Read from sources, not yet reviewed
How close this is to real life
The top step is something a person would feel or care about. The bottom is a guess from software. Filled steps are where evidence exists for this substance.
■Living longer, or avoiding a major eventEvidence recorded. Death, a heart attack, a stroke, a hospital stay.1 registered measure of this kind. No reviewed result.
□What a body can do day to dayNo evidence recorded. Walking, dressing, breathing, recovering.No registered study measures this.
□Measured performanceNo evidence recorded. How much was lifted, how far was run, how fast.No registered study measures this.
■Symptoms and quality of lifeEvidence recorded. Pain, tiredness, mood, sleep, as the person rated it.5 registered measures of this kind.
■A number that stands in for healthEvidence recorded. Cholesterol, blood sugar, bone density. A stand-in, not the thing itself.8 registered measures of this kind.
■A step measured inside a personEvidence recorded. Something measured in human tissue or human cells.A human record sits on the stored organism ladder.
■AnimalsEvidence recorded. Mice, rats, dogs. Useful for ideas, not proof about people.Stored records in Mouse. A result in animals says what to test next. It does not say what happens in people.
■Cells in a dishEvidence recorded. Cells or chemistry on a bench, far from a whole body.Stored mechanism abstracts describe steps measured in cells or tissue.
□A guess from softwareNo evidence recorded. Nobody measured it. RNAWiki never publishes one as a finding.RNAWiki stores no prediction for this record. Software can suggest a link. RNAWiki does not publish one as a finding.
Higher on these steps means closer to something a person would feel. It does not mean better done.
What it changes in the body◇Read from sources, not yet reviewed
The path through the body
From what a person takes to what changes. A solid line is a step measured in people. A dashed line is a step nobody has measured that way.
Start
Levothyroxine
What a person takes: Oral tablet in twelve strengths, plus soft-gel capsules, an oral solution and an intravenous formulation for myxoedema coma.
The measurement behind this step
Taken once daily on an empty stomach with water, kept consistent relative to food and to interacting medicines. The wide range of tablet strengths exists because dosing is titrated in small increments against a laboratory value with a six-week lag. Soft-gel and solution formulations exist because tablet dissolution depends on gastric acid, which several common drugs suppress.
Getting in
Absorbed in the upper small intestine, and easily interfered with
Most of the tablet is absorbed in the first part of the small intestine. Food, calcium, iron and acid-reducing medicines all cut how much gets through.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Oral absorption is roughly 40 to 80% and occurs chiefly in the jejunum and upper ileum, requiring gastric acid for tablet dissolution. Calcium and iron salts, proton pump inhibitors, bile acid sequestrants, sucralfate and soy protein all reduce it. The elimination half-life is about 7 days, which is why a dose change takes six weeks to show up on a TSH measurement.
It travels bound to proteins, and needs a transporter to enter a cell
Almost all of the hormone in your blood is stuck to carrier proteins; only a tiny free fraction is available. Getting into a cell requires a specific transporter rather than simple diffusion.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
More than 99.95% of circulating T4 is bound to thyroxine-binding globulin, transthyretin and albumin. Cellular entry is transporter-mediated, principally by MCT8 (SLC16A2) and OATP1C1. Loss-of-function MCT8 mutations produce the Allan-Herndon-Dudley syndrome, in which serum hormone is high and brain tissue is hypothyroid — direct evidence that serum concentration and tissue exposure can diverge.
Each tissue converts it to the active form at its own rate
T4 is largely a prohormone. Selenium-containing enzymes inside each tissue strip one iodine atom off to make the far more active T3, and each tissue controls how much it makes.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Type 1 and type 2 iodothyronine deiodinases (DIO1, DIO2) catalyse outer-ring deiodination of T4 to T3; type 3 (DIO3) inactivates both by inner-ring deiodination. Local deiodinase activity sets intracellular T3 independently of the circulating level, which is the mechanistic argument for giving T4 rather than T3 — the tissue keeps control of its own exposure.
T3 binds a receptor already sitting on DNA and flips it from off to on
The receptor is parked on the gene before the hormone arrives, holding it switched off. When the hormone binds, the receptor swaps its silencing partners for activating ones and the gene turns on.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Thyroid hormone receptors alpha and beta occupy thyroid hormone response elements as heterodimers with the retinoid X receptor, bound to corepressors NCoR and SMRT with histone deacetylase activity in the unliganded state. T3 binding triggers corepressor release and coactivator recruitment, switching transcription of genes for mitochondrial oxidative metabolism, sodium-potassium ATPase, beta-adrenergic receptor density and hepatic LDL receptor expression.
The pituitary stops shouting, and in overt disease the person recovers
As hormone is restored, the pituitary lowers its demand signal and TSH falls back into range. In genuine hypothyroidism symptoms resolve. Where the gland was working adequately already, the number changes and nothing else does.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Negative feedback at the pituitary thyrotroph suppresses TSH beta subunit transcription, and TSH is what dosing is titrated on. In TRUST, thyrotropin fell from 6.40 to 3.63 mIU/L on levothyroxine against 5.48 on placebo (p<0.001), while the two primary symptom outcomes differed by 0.0 and 0.4 points on scales where 9 points is the threshold for clinical importance.
No suggested links are held for this record, so nothing is hidden from this path.
What we know
The record describes 5 steps from taking it to an effect in a person.
How we know it
Each step names the study behind it in the technical detail beside it.
What this does not prove
A change inside the body is a reason to look. It is not a result in a person.
Why it matters
A reader can see exactly where the chain stops being measured in people.
What we still do not know
No reviewed claim binds any of these steps to a named population.
What it would be like to take◇Read from sources, not yet reviewed
Felt, measured, or meaningful
Three different things that get called the same word. Registered studies measured all three, and mixing them is how a blood test becomes a health claim.
Felt
Things a person could notice without a test.
hamilton rating scale for depression
thyroid symptom questionnaire
beck depression inventory
satiety
health related quality of life
Measured
Things only a test, a scale or a device shows.
insulin sensitivity
cholesterol
bone mineral density
effects on gut inflammation parameter
pk of ee and net maximum observed plasma concentration
blood pressure
maximum plasma concentration of triiodothyronine
time to maximum plasma concentration of triiodothyronine
Meaningful
Things that change how a life goes, not only a number.
all cause mortality
A registered study says what someone planned to measure. It does not say what they found. A number moving is not the same as a life going better. The two are shown apart here.
Felt, but not shown to help. A person notices a change. No study showed it leads anywhere good.
Measured, but not felt. A number moves. The person notices nothing. Both can be true.
Measured, but not shown to matter. A number moves in the good direction. Nobody showed that lives went better.
Matters, but takes years. The result that counts may take longer than anyone would keep watching.
Names that fit none of the three (26)
executive function
resting energy expenditure
bioequivalence
biochemical parameters
preterm birth
neurodevelopmental outcome
lipid profile
study feasibility
dose adjustments
thyroid stimulating hormone
cardiac output
newborn birth weight
liver fat content
pregnancy
pk of ee and net auc from time 0 extrapolated to infinity
pk of ee and net terminal phase half life
recruitment rate
graft function
short term change in weight
energy expenditure
These are harms, study-process measures, or names the rules did not recognise. They are shown rather than dropped.
What it would be like to take◇Read from sources, not yet reviewed
How long anything takes
Nine different lengths of time that get confused with each other. None of them is worked out from another.
Before anything is noticed.RNAWiki does not store this separately, and never works it out from another figure on this page.
Before a test result moves.RNAWiki does not store this separately, and never works it out from another figure on this page.
Before performance moves.RNAWiki does not store this separately, and never works it out from another figure on this page.
How long the result was watched.No finished study window is recorded for a study that tested this substance.
How long people took it.How long people actually took it is not stored. The study window is not the same thing.
How long people were followed.Follow-up length is not stored separately. It is never read off the study window, which would be a different thing.
How fast the body clears it. 6 to 7 days days
Read from the label, which states: “Hormone Ratio in Thyroglobulin Biologic Potency t 1/2 (days) Protein Binding (%) * Levothyroxine (T4) 10 to 20 1 6 to 7 ** 99.96”
How long effects linger.RNAWiki does not store this separately, and never works it out from another figure on this page.
Beyond the studies. Nothing is recorded about the long term.
The longest finished study sets the edge of what anyone measured.
A study window is not how long people took it, and neither is how long they were followed. Where RNAWiki holds only one of the three, it shows one.
What is missing or unclear◇Read from sources, not yet reviewed
Were people like you studied?
RNAWiki cannot tell whether a study fits you. It can show who was in it, and where the result stops carrying.
Who was studied
People similar to this profile were included.
One of the most-dispensed prescription drugs in the United States and in many other countries. On the WHO Model List of Essential Medicines. A substantial fraction of prescriptions are written for subclinical hypothyroidism or for symptoms in people whose thyroid tests are normal.
Who is missing from the studies
Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
What the label states about particular groups
On pediatric, the label states: “Myxedema coma is a disease of the elderly.”
US prescribing information · 4e9adc35-3aba-4a0d-9c4e-7e7ee2ffdabd · read 2026-08-30
On older people, the label states: “and Patients with Underlying Cardiovascular Disease See Section 2, Dosage and Administration , for full prescribing information in the geriatric patient population.”
US prescribing information · 4e9adc35-3aba-4a0d-9c4e-7e7ee2ffdabd · read 2026-08-30
On people who are pregnant, the label states: “Studies in pregnant women treated with oral levothyroxine to maintain a euthyroid state have not shown an increased risk of fetal abnormalities.”
US prescribing information · 4e9adc35-3aba-4a0d-9c4e-7e7ee2ffdabd · read 2026-08-30
On people who are breastfeeding, the label states: “Adequate replacement doses of thyroid hormones are required to maintain normal lactation.”
US prescribing information · 4e9adc35-3aba-4a0d-9c4e-7e7ee2ffdabd · read 2026-08-30
Where the result stopped carrying
TRUST: both co-primary symptom outcomes, at 0.0 and 0.4 points against a 9-point threshold
The prospectively planned 80-plus analysis, at p=0.53 and p=0.96
T4-T3 combination therapy across 11 randomised trials, on pain, depression, anxiety, fatigue, quality of life, weight and every lipid fraction
This is a scope explorer, not a diagnosis engine.
It shows who was studied so you can see whether people similar to you were included.
RNAWiki cannot tell whether a study fits you. It can show who was in it.
What it would be like to take◇Read from sources, not yet reviewed
Why it might seem to do nothing
A real effect and a noticed effect are different things. These are the recorded reasons the two come apart.
It was studied for a different goal
The studies measured something else entirely.
On this record: Some registered studies measured things that match no goal on this page.
It was studied in different people
The people in the studies were not much like the reader.
On this record: Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
A different form was studied
The studied form is not the form on the shelf.
On this record: This record is linked to 1 related forms. Evidence does not carry across all of them.
The evidence may simply be wrong
Small early studies often do not hold up.
On this record: RNAWiki has not yet published a reviewed conclusion for this use.
Other reasons RNAWiki checked and found nothing for (9)
There was nothing to correct
Where a level is already normal, topping it up may change nothing. Nothing in this record points to this reason.
Something else had to happen too
In the studies it was paired with training, a diet or another treatment. Nothing in this record points to this reason.
The change is too small to feel
A real change can still sit below what a person notices. Nothing in this record points to this reason.
Day-to-day swing hides it
Sleep, food, stress and time of day move most numbers more than this would. Nothing in this record points to this reason.
Not enough time yet
The studies ran longer than the person has waited. Nothing in this record points to this reason.
It was not taken as studied
Missed days change the result, and studies count them. Nothing in this record points to this reason.
Something else changed at the same time
Two changes at once cannot be told apart afterwards. Nothing in this record points to this reason.
The product may not be what it says
Contents of a sold product are not always what the label states. Nothing in this record points to this reason.
No recorded reason
RNAWiki has nothing stored that would explain it. Nothing in this record points to this reason.
None of these is a reason to take more. Taking more is not a step this page ever suggests.
What it would be like to take◇Read from sources, not yet reviewed
What taking it involves
The recorded facts about getting hold of it and using it. Nothing here is a suggestion about what you should do.
How it is supplied
Given by a clinician
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
Read from the recorded approval status.
No source is stored against this line.
Form and route
Oral tablet in twelve strengths, plus soft-gel capsules, an oral solution and an intravenous formulation for myxoedema coma
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form and route recorded on this substance.
No source is stored against this line.
Who oversees it
RNAWiki has not recorded a supervision or regulatory status for this substance.
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
No register row and no identity class settled the question.
No source is stored against this line.
What is in the pack
Taken once daily on an empty stomach with water, kept consistent relative to food and to interacting medicines. The wide range of tablet strengths exists because dosing is titrated in small increments against a laboratory value with a six-week lag. Soft-gel and solution formulations exist because tablet dissolution depends on gastric acid, which several common drugs suppress.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on how this is sold and what that means for what is in the pack.
No source is stored against this line.
Where it is registered
Regulatory records are listed in the technical disclosure at the foot of this page.
# Counted from records
Where this came from
A count of rows RNAWiki holds. It describes our records, not your body.
Register entries are stored per jurisdiction and shown with their dates.
No source is stored against this line.
Why people stop
Not recorded.
∅ Nothing recorded
Where this came from
RNAWiki holds nothing here and says so rather than guessing.
No record of why people stopped taking it is stored for this substance.
No source is stored against this line.
What it would be like to take◇Read from sources, not yet reviewed
What can go wrong
Sorted by where each line came from. A regulator's label and a report somebody sent in are not the same kind of fact.
·Worth asking a clinician aboutWritten into the record from the studies named on this page
The US label carries a boxed warning that thyroid hormones must not be used for obesity or weight loss, alone or with other agents, because doses within the normal range are ineffective for weight reduction and larger doses may produce serious or life-threatening toxicity. Over-replacement produces the features of thyrotoxicosis and, in the Tayside cohort, was associated with atrial fibrillation, cardiovascular disease and fractures. Absorption is reduced by calcium, iron, proton pump inhibitors, bile acid sequestrants and soy.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
These are reports people sent to a regulator. They do not show the medicine caused the reaction.
Nobody counted how many people took the medicine and reported nothing.
The same event can be reported more than once, and many reports are incomplete.
News coverage, lawsuits and new warnings change how often people report.
A count is not a rate and not a risk.
Levothyroxine appears in spontaneous reports to regulators. Across the 10 most-reported reaction terms, 491 reaction mentions were counted. One report can name several reactions.
open-targets-adr · recorded 2026-06-24 · a recorded source, not a stored snapshot
Over a long time. No completed tested study window is recorded, so long-term effects are not established by the registry record.
Groups the studies covered thinly. Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
What is missing or unclear◇Read from sources, not yet reviewed
Does the exact form matter?
Evidence belongs to the exact thing that was tested. A different salt, a different mixture or a different preparation is a different question.
The form that was studied
Oral tablet in twelve strengths, plus soft-gel capsules, an oral solution and an intravenous formulation for myxoedema coma
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form used in the studies cited on this page.
No source is stored against this line.
What is sold
The wide range of tablet strengths exists because dosing is titrated in small increments against a laboratory value with a six-week lag. Soft-gel and solution formulations exist because tablet dissolution depends on gastric acid, which several common drugs suppress.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on which forms are sold and how they compare.
No source is stored against this line.
What is recorded as being sold
701 products list this as an active ingredient in the United States drug directory. 630 of them contain it and nothing else.
FDA National Drug Code directory · 71335-3116 · read 2026-08-29
They are sold as capsule, injection, injection, powder, lyophilized, for solution, injection, solution, liquid and powder, taken intravenous, oral and sublingual.
FDA National Drug Code directory · 71335-3116 · read 2026-08-29
The regulator's established pharmacologic class for it is thyroxine [cs] and l-thyroxine [epc].
FDA National Drug Code directory · 71335-3116 · read 2026-08-29
338 published labels name it as an active ingredient. 288 of them describe this substance alone, which is where its own label text on this page comes from.
US prescribing information · f31a35cb-fc54-8872-e053-2a95a90ad8e7 · read 2026-08-29
Those labels are classed as human otc drug and human prescription drug.
US prescribing information · f31a35cb-fc54-8872-e053-2a95a90ad8e7 · read 2026-08-29
Levothyroxine sodium is tablets (functional scoring) at Tablets: 25, 50, 75, 88, 100, 112, 125, 137, 150, 175, 200, and 300 mcg, recorded as prescription product; fda label in effect 2026-03-24 in the United States.
US prescribing information · 008de8fd-150f-4022-8ccb-c8bfa94875c7 · read 2026-08-27
Recorded price in US: 0.03568–0.09986 USD per one unit as the pricing file counts it — a tablet, capsule, patch or single item, across 305 priced products whose strengths and pack forms differ, as of 2026-08-26, paid by retail pharmacies buying the product, as surveyed by the Centers for Medicare & Medicaid Services. It is not a list price, an insurance price, or what anyone pays at a counter..
Recorded source · 2026-08-26 · read 2026-08-28
Evidence carries across two names for one substance. It does not carry across a salt, a mirror form or a mixture.
Evidence on this page does not automatically apply to this one.
What it would be like to take◇Read from sources, not yet reviewed
What you could measure
This one is decided with a clinician, so this section holds questions to ask rather than a plan to run.
RNAWiki could not confidently classify this substance, so no self-experiment plan is offered.
Questions worth asking
Which of the trials of Levothyroxine studied people like me?
What was measured, and for how long?
Was the result a laboratory value or a health outcome?
What would we watch for, and when would we stop?
Tracking can show whether something changed for you. It cannot show what caused it.
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What is missing or unclear◇Read from sources, not yet reviewed
Claims that go past the evidence
Things said about this substance that sound reasonable, and the exact step that is missing between the evidence and the claim.
✗Goes past the evidence
That normalising a raised thyrotropin in subclinical hypothyroidism relieves symptoms — the surrogate corrects and the symptoms do not
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That older or frailer patients benefit more — the 80-plus analysis found differences of 1.3 and -0.1 points
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That adding T3 helps people who still feel unwell on T4 — eleven trials in 1,216 patients found no difference on any outcome
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That the TRUST and meta-analysis results say anything about overt hypothyroidism, which they did not study and where replacement is not in question
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
What is missing or unclear◇Read from sources, not yet reviewed
What nobody knows yet
Open questions, each with why it is open and what would close it.
Missing populations
Which groups were under-represented in the studies has not been recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing long-term data
No completed tested study window is recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
No reviewed conclusion
RNAWiki has not yet published a reviewed conclusion for this use.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing interaction studies
No interaction was found in the registers checked. Not finding one is not the same as showing there is none.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Formulation uncertainty
Several salts, forms or products of Levothyroxine are recorded. Results from one form may not transfer to another.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Mechanism not reviewed
No reviewed mechanism story exists for this substance.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
What happened in people◇Read from sources, not yet reviewed
Check any of this yourself
Every line above traced back to the study it came from. This is the technical layer, and the vocabulary changes here.
Every line above can be traced to the study named beside it. Follow the link and read it.
TRUST: TSH normalised, symptoms did not move at all
In plain words
Seven hundred and thirty-seven adults over 65 with a mildly raised thyroid-stimulating hormone took levothyroxine or placebo for a year. The blood number corrected. The difference in symptoms between the two groups was zero.
What was measured
Change in Hypothyroid Symptoms and Tiredness scores at 1 year against a 9-point clinical importance threshold
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
TRUST randomised 737 adults aged at least 65 with persisting subclinical hypothyroidism (thyrotropin 4.60 to 19.99 mIU/L, free thyroxine within the reference range) to levothyroxine (n=368, starting at 50 mcg daily or 25 mcg if under 50 kg or with coronary disease, titrated to thyrotropin) or placebo with mock dose adjustment (n=369). Mean age was 74.4 years. Mean thyrotropin was 6.40 mIU/L at baseline and at 1 year had fallen to 3.63 on levothyroxine against 5.48 on placebo (p<0.001) at a median dose of 50 mcg. The two primary outcomes, change in the Hypothyroid Symptoms score and the Tiredness score at 1 year on a 0-to-100 scale with a minimum clinically important difference of 9 points, showed between-group differences of 0.0 (95% CI -2.0 to 2.1) and 0.4 (-2.1 to 2.9). No secondary outcome showed benefit.
Written into the record, not signed off as a reviewed claim
The oldest patients, where the case seemed strongest, showed the same nothing
In plain words
A planned combined analysis in people aged 80 and over — the group most often described as needing treatment — found no improvement in symptoms or fatigue.
What was measured
ThyPRO hypothyroid symptoms and tiredness domain scores at 1 year in adults aged 80 and older
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
A prospectively planned combined analysis pooled the participants aged 80 and older from TRUST with a second randomised trial, 251 community-dwelling adults with subclinical hypothyroidism, mean age 85, of whom 118 (47%) were women and 212 (84%) completed. 112 received levothyroxine and 139 placebo. The hypothyroid symptoms score fell from 21.7 to 19.3 on levothyroxine and from 19.8 to 17.4 on placebo: adjusted between-group difference 1.3 (95% CI -2.7 to 5.2), p=0.53. The tiredness score rose from 25.5 to 28.2 on levothyroxine and from 25.1 to 28.7 on placebo: adjusted difference -0.1 (-4.5 to 4.3), p=0.96. Both are far below the 9-point minimum clinically important difference. At least one adverse event occurred in 29.5% on levothyroxine and 28.8% on placebo.
Written into the record, not signed off as a reviewed claim
Twenty-one trials and 2,192 adults: no benefit on quality of life or symptoms
In plain words
Pooling every randomised trial of thyroid hormone for subclinical hypothyroidism found the treatment reliably normalised the blood test and reliably failed to change how people felt.
What was measured
Standardised mean difference in general quality of life and thyroid-related symptoms across 21 randomised trials
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Feller and colleagues screened 3,088 publications and included 21 randomised trials with 2,192 adults randomised, comparing thyroid hormone therapy with placebo or no therapy in non-pregnant adults with subclinical hypothyroidism, minimum follow-up 3 months. Thyroid hormone therapy lowered mean thyrotropin into the reference range (0.5 to 3.7 mIU/L against 4.6 to 14.7 on placebo) but was not associated with benefit in general quality of life (n=796; standardised mean difference -0.11, 95% CI -0.25 to 0.03; I-squared 66.7%) or thyroid-related symptoms (n=858; SMD 0.01, -0.12 to 0.14; I-squared 0.0%). Risk of bias was low and the GRADE quality of evidence was judged moderate to high. The stated conclusion is that these findings do not support routine use of thyroid hormone therapy in adults with subclinical hypothyroidism.
Written into the record, not signed off as a reviewed claim
Adding T3 to T4 failed on every symptom measured, across 11 trials
In plain words
Patients who still feel unwell on levothyroxine often ask for the second thyroid hormone to be added. Eleven randomised trials in 1,216 patients found no advantage on any measure.
What was measured
Standardised mean differences in pain, depression, anxiety, fatigue and quality of life, combination versus monotherapy
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
Grozinsky-Glasberg and colleagues pooled 11 randomised trials with 1,216 patients randomised, comparing T4-T3 combination therapy with T4 monotherapy in adults with clinical hypothyroidism. No difference was found for bodily pain (SMD 0.00, 95% CI -0.34 to 0.35), depression (0.07, -0.20 to 0.34), anxiety (0.00, -0.12 to 0.11), fatigue (-0.12, -0.33 to 0.09) or quality of life (0.03, -0.09 to 0.15), nor for body weight, total cholesterol, triglycerides, LDL or HDL. Adverse events did not differ. The 2014 American Thyroid Association task force reviewed thyroid extracts, synthetic combination therapy, liothyronine and compounded preparations and concluded that levothyroxine should remain the standard of care.
Written into the record, not signed off as a reviewed claim
Over-replacement carries measured harm; slightly-low TSH does not
In plain words
A Scottish cohort of nearly eighteen thousand people on thyroxine found more heart disease, more rhythm disturbance and more fractures in those whose TSH was fully suppressed — but not in those whose TSH was merely on the low side.
What was measured
Adjusted hazard ratios for cardiovascular disease, dysrhythmias and fractures by TSH category in 17,684 treated patients
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Flynn and colleagues linked regional datasets covering all 17,684 patients on thyroxine replacement in Tayside, Scotland, between 1993 and 2001, categorising them by TSH: suppressed (≤0.03 mU/L), low (0.04-0.4), normal (0.4-4.0) or raised (>4.0). Against the normal category, patients with a raised TSH had adjusted hazard ratios of 1.95 (1.73-2.21) for cardiovascular disease, 1.80 (1.33-2.44) for dysrhythmias and 1.83 (1.41-2.37) for fractures. Patients with a suppressed TSH had 1.37 (1.17-1.60), 1.6 (1.10-2.33) and 2.02 (1.55-2.62). Patients with a low but unsuppressed TSH had no increased risk of any of the three: 1.1 (0.99-1.123), 1.13 (0.88-1.47) and 1.13 (0.92-1.39). This is an observational cohort and cannot separate the dose from the reason for it.
Written into the record, not signed off as a reviewed claim
One of the most-prescribed drugs in America had no approved application until 2002
In plain words
Levothyroxine products were sold in the United States for decades without ever having gone through the modern approval process, because they predated it. The FDA required applications in the late 1990s after repeated potency and stability problems.
What was measured
Original approval dates on file for levothyroxine sodium products in Drugs@FDA
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Because orally administered levothyroxine sodium products entered the market before the modern efficacy and approval requirements applied to them, they were marketed for decades as unapproved drugs. Following documented potency and stability problems the FDA required manufacturers to submit new drug applications. The Drugs@FDA record shows the resulting approvals arriving in the 2000s: UNITHROID on 21 August 2000, LEVOXYL on 25 May 2001, LEVO-T on 1 March 2002, EUTHYROX on 31 May 2002 and SYNTHROID — by then already among the most-dispensed prescriptions in the country — on 24 July 2002. This is the reverse of the usual pattern on this site: not a claim outrunning its evidence, but a product outrunning its regulatory file, and the potency specification that resulted is the reason brand-to-generic substitution is treated cautiously for this molecule.
Source
Drugs@FDA application records: SYNTHROID NDA 021402 (approved 24 July 2002), UNITHROID NDA 021210 (21 August 2000), LEVOXYL NDA 021301 (25 May 2001), EUTHYROX NDA 021292 (31 May 2002)
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
verified
Review state
Written into the record, not signed off as a reviewed claim
How many documents were read
287 documents were read for this substance.
RNAWiki source record
5 of them state the same proteinBinding, and they agree.
RNAWiki source record
Where else this substance is registered
FDA substance identifier (UNII)
9J765S329G
CAS registry number
51-48-9
PubChem compound
5819
RxNorm concept
10582
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Every public sentence names a source
The opening statement carries the origin: Reviewed first-read answer.
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Trial roles classified for highlighted evidence
No registered study is classified as testing this substance.
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enforced by the copy-contract test over the rendered page
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Safety mode resolved
No register row and no identity class settled the question.
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Canonical metadata present
slug and display name present
What is missing or unclear◇Read from sources, not yet reviewed
How this medicine reached us
Kept near the foot of the page. A historical event moves up only when it changes something about this substance today.
What the approval register records
34 approved applications cover products containing this substance. The earliest was NDA021210, approved 20000821 to STEVENS J.
This order is fixed in code and does not count clicks or time on the page.
What is not here
3 questions this page could not answer
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Everything above is built from what is below. This layer keeps the technical vocabulary, record identifiers and every stored row, so a reader who wants to check the page can.
The older medicine-wide conclusion held in this record
Written for a clinical reader, and about the medicine as a whole rather than about one indication, population and set of trials. RNAWiki does not treat it as a programme conclusion and no reviewer has signed it off in that form. It is here word for word because it is what the record holds.
Synthetic thyroxine is straightforward replacement therapy in overt hypothyroidism and one of the most useful drugs in medicine there, but in 737 older adults with subclinical hypothyroidism it normalised TSH and produced a between-group difference of 0.0 points on hypothyroid symptoms and 0.4 points on tiredness against a threshold for clinical importance of 9.
Recorded evidence blocks (15)
Q1
What did Levothyroxine's largest trial (4657 people) and its longest (15 years) measure?
4657 people in Levothyroxine's largest registered study, 15 years in its longest registered window, measuring All cause mortality. ClinicalTrials.gov · 2026-09-01
35 phase4, 32 na, 22 phase2, 18 phase3, 16 phase1, 11 na or unstated, 1 early phase1; NCT07380854; 2037-02-26; no ageing endpoint recorded. Last human test completed 2026, NCT07754370.
Interpretation These counts include studies where Levothyroxine was a comparison treatment, a background treatment or an exposure in an observational study, and the longest window may be a planned end date. Trial roles have not yet been classified for this record.
Show the evidence
phase4
35
na
32
phase2
22
phase3
18
phase1
16
na or unstated
11
2 more recorded rows
early phase1
1
Last recorded human testNCT07754370
2026-07-20
recorded 2026-09-01 · last checked 2026-09-04
Q2
From mouse to human: where has Levothyroxine shown lifespan?
7 recorded entries; human; also "Synthroid® Tablets 300 μg", "Levothyroxine Sodium Tablets 200 mg", "Synthroid Tablets 200 mg"
Show the evidence
human
NCT00647855
Levothyroxine Sodium Tablets 300 μg
NCT00647855
Synthroid® Tablets 300 μg
NCT00648557
Levothyroxine Sodium Tablets 200 mg
NCT00648557
Synthroid Tablets 200 mg
NCT00648700
Levothroid® Tablets 300 μg
NCT00648882
SYNTHROID® 300 mcg Tablets
1 more recorded row
humanNCT06041204
Levothyroxine 25 Mcg (0.025 Mg) Oral Tablet
recorded 2026-09-01 · last checked 2026-09-04
Q5
More Levothyroxine was worse in human: at what point?
U-shaped in human: "Considering the U-shaped association between thyroidstimulating hormone (TSH) and hypertensive disorders of pregnancy in some reports, we decided to investigate the effect of levothyroxine treatment on GH and PE in pregnant women with subclinical hypothyroidism (SCH) overt hypothyroidism (OH), and autoimmune thyroid…" Europe PMC · dose-response search · 2025-01-01
5 recorded sentences naming Levothyroxine; U-shaped, dose-response, dose response
Show the evidence
U-shaped
PMID 39976090
"Considering the U-shaped association between thyroidstimulating hormone (TSH) and hypertensive disorders of pregnancy in some reports, we decided to investigate the effect of levothyroxine treatment on GH and PE in pregnant women with subclinical hypothyroidism (SCH) overt hypothyroidism (OH), and autoimmune thyroid diseases."
PMID 38536878
"A nonlinear, U-shaped relationship was observed between the daily dose of levothyroxine and the risk of DM (P = .021), but the risk of hyperlipidemia was low with high doses of levothyroxine in patients with DTC (P = .003)."
PMID 34718625
"There was a U-shaped dose-dependent relationship between the levothyroxine dosage and type 2 diabetes mellitus risk."
dose-responsePMID 36457560
"CV outcome and dose-response trials are needed to understand better the role of levothyroxine replacement treatment for a safer prescription in this clinical setting."
dose responsePMID 31617168
"Despite the dose response of this drug being more carefully titrated nowadays, several papers still report that a significant fraction of patients treated with levothyroxine demonstrate a TSH which is not on target."
recorded 2025-01-01 · last checked 2026-09-04
Q6
Levothyroxine's half-life is 6 to 7 days — which schedules were studied?
6 to 7 days, the half-life Levothyroxine's label states. openfda-label · 58f4dc90-3648-49dc-a7e1-baf918a773b5 · 2026-08-27
bioavailability 40% to 80% %.
Show the evidence
half life
6 to 7 days days; Hormone Ratio in Thyroglobulin Biologic Potency t 1/2 (days) Protein Binding (%) * Levothyroxine (T4) 10 to 20 1 6 to 7 ** 99.96
bioavailability
40% to 80% %; Absorption of orally administered T4 from the gastrointestinal tract ranges from 40% to 80%. The majority of the levothyroxine sodium dose is absorbed from the jejunum and upper ileum.
recorded 2026-08-27 · last checked 2026-09-04
Q7
Could one person measure Levothyroxine's effect on executive function?
Executive function: measured in Levothyroxine's trials.
Interpretation executive function is the recorded endpoint.
Show the evidence
biomarkers
executive function; 2026-09-01
resting energy expenditure; 2026-09-01
bioequivalence; 2026-09-01
biochemical parameters; 2026-09-01
insulin sensitivity; 2026-09-01
preterm birth; 2026-09-01
14 more recorded rows
biomarkers
neurodevelopmental outcome; 2026-09-01
biomarkers
hamilton rating scale for depression; 2026-09-01
biomarkers
cholesterol; 2026-09-01
biomarkers
all cause mortality; 2026-09-01
biomarkers
thyroid symptom questionnaire; 2026-09-01
biomarkers
lipid profile; 2026-09-01
biomarkers
study feasibility; 2026-09-01
biomarkers
beck depression inventory; 2026-09-01
biomarkers
dose adjustments; 2026-09-01
biomarkers
bone mineral density; 2026-09-01
biomarkers
effects on gut inflammation parameter; 2026-09-01
biomarkers
satiety; 2026-09-01
biomarkers
thyroid stimulating hormone; 2026-09-01
biomarkers
cardiac output; 2026-09-01
half life
2026-09-04; halfLife; days; 6 to 7 days; 2026-08-27
human trials at or under30
32
smallest human trial
0; NCT00770016; NA; the smallest recorded human enrolment at or below 30; the registry states no direction of its result; TERMINATED
Q8
Which of adverse events, all cause mortality and beck depression inventory did Levothyroxine's trials measure?
adverse events, all cause mortality and beck depression inventory lead 40 outcome terms across Levothyroxine's trials. ClinicalTrials.gov · 2026-09-01
Interpretation biochemical parameters, insulin sensitivity, preterm birth, neurodevelopmental outcome, hamilton rating scale for depression and cholesterol follow.
Show the evidence
executive function
1
resting energy expenditure
1
bioequivalence
1
biochemical parameters
1
insulin sensitivity
1
preterm birth
1
14 more recorded rows
neurodevelopmental outcome
1
hamilton rating scale for depression
1
cholesterol
1
all cause mortality
1
thyroid symptom questionnaire
1
lipid profile
1
study feasibility
1
beck depression inventory
1
dose adjustments
1
bone mineral density
1
effects on gut inflammation parameter
1
satiety
1
thyroid stimulating hormone
1
cardiac output
1
recorded 2026-09-01 · last checked 2026-09-04
Q9
Which of Levothyroxine's 18 ongoing trials reports first?
Health-Related Quality of Life (HRQOL) - Short Form 36 Physical Component Score; Hypothyroidism-free survival; latest 2037-03
Show the evidence
Trial
NCT03977207
"A Randomized Controlled Trial of Thyroid Hormone Supplementation in Hemodialysis Patients"; n 336; "Health-Related Quality of Life (HRQOL) - Short Form 36 Physical Component Score"; 2025-11-30
NCT05316922
"TSH Suppression During Radiotherapy on Thyroid Site to Prevent Iatrogenic Hypothyroidism in Pediatric Cancer Patients"; n 68; "Hypothyroidism-free survival"; 2029-09-30
NCT05526144
"Thyroid Hormone for Treatment of Nonalcoholic Steatohepatitis in Veterans"; n 128; "Improvement in Nonalcoholic fatty liver disease activity score (NAS) by 2 points"; 2029-12-31
NCT06041204
"Best Treatment for Women With Both (Polycystic Ovary Syndrome) PCOS and Subclinical Hypothyroidism"; n 200; "Pregnancy rate"; 2026-06-28
NCT06073665
"Dosing of LT4 in Older Individuals"; n 228; "Thyroid-Related Quality of Life Patient-Reported Outcome Quality of Life scale"; 2028-04-01
NCT06087068
"Thyroxine Replacement Therapy After Lobectomy for Low-risk Papillary Thyroid Carcinoma"; n 140; "recurrence"; 2026-12-31
12 further recorded trials
NCT06345339
"A Study to Assess the Safety and Efficacy of Oral Armour Thyroid Compared to Synthetic T4 for the Treatment of Primary Hypothyroidism in Adult Participants"; n 2800; "Percentage of Participants who Achieve Thyroid-Stimulating Hormone (TSH) Response"; 2028-06
NCT06428097
"Levothyroxine Supplementation for Heart Transplant Recipients"; n 97; "Number of participants who receive Levothyroxine's vasopressor use compared to number of participants who receive normal saline's vasopressor use."; 2027-03-01
NCT06647602
"Thyroid Hormone Replacement After Radio Iodine: Value and Efficacy"; n 40; "TSH after two weeks of TH substitution"; 2028-12-31
NCT06652113
"Effect of HCQ Combined With LT4 on LBR in Euthyroid Women With URPL and TPO-Ab"; n 796; "Birth of a living child beyond 28 weeks"; 2037-03
NCT06653907
"Levothyroxine Intervention in Pregnant Women with TSH （2.5 MIU/L-upper Limit of Reference Range） and Negative Thyroid Peroxidase Antibody"; n 400; "Rate of fetal loss"; 2027-10-31
NCT06731764
"Novel Approaches to the Treatment of Hypothyroidism"; n 90; "Changes in Total Cholesterol"; 2028-06-30
NCT07332273
"Levothyroxine as Adjuvant to a Hypocaloric Diet for the Treatment of Obesity."; n 286; "Change in body weight (kg) from baseline to Month 3"; 2027-05
NCT07380854
"Thyroid Hormone Replacement After Coronary Artery Bypass Grafting for Patients With Subclinical Hypothyroidism"; n 338; "A composite of MACE within 4months after surgery"; 2037-02-26
NCT07393165
"Levothyroxine Treatment on Cardiac Function in Children With Subclinical Hypothyroidism"; n 40; "Assessment of left ventricle systolic function"; 2026-05-01
NCT07424183
"T4/T3 Therapy in Hypothyroidism"; n 60; "ThyPRO Composite QOL Scale"; 2027-11
NCT07568574
"Impact of Medically Supervised Performance-Enhancing Substances (PES) on Elite Athletes"; n 60; "The incidence and severity of Treatment-related adverse events (TRAEs), including adverse events (AEs) and serious adverse events (SAEs), as assessed by the study physicians from baseline to 5.5 years after enrollment."; 2033-03-01
NCT07625722
"Thyroxine Supplementation in Small for Gestational Age (SGA) Infants With Birth Weight <1500g and TSH 6-20 mIU/ml"; n 106; "Cognitive function evaluated by Bayley-IV"; 2029-06-20
recorded 2026-09-01 · last checked 2026-09-04
Q10
Which running trial of Levothyroxine could settle lifespan?
NCT05316922 measures Hypothyroidism-free survival, reading out 2029-09-30.
1 open trial; n 68; "TSH Suppression During Radiotherapy on Thyroid Site to Prevent Iatrogenic Hypothyroidism in Pediatric Cancer Patients"
Show the evidence
TrialNCT05316922
"TSH Suppression During Radiotherapy on Thyroid Site to Prevent Iatrogenic Hypothyroidism in Pediatric Cancer Patients"; n 68; "Hypothyroidism-free survival"; 2029-09-30
Q11
Which 48 trials of Levothyroxine posted no result?
Posted no result
48 of 48 completed trials
Registrations
NCT00648557, NCT00647855, NCT01465633, NCT01465646, NCT00715572 and NCT00498238, and 42 more
Completion dates
oldest 2003-03; newest 2024-01-20
Show the evidence
Trial
NCT00648557
2003-03
NCT00647855
2003-06
NCT01465633
2003-11
NCT01465646
2003-12
NCT00715572
2004-05
NCT00498238
2005-09
14 further recorded trials
NCT00648700
2005-09
NCT00524238
2006-08
NCT00648882
2007-05
NCT01528839
2008-08
NCT00846755
2008-12
NCT00941551
2008-12
NCT01189344
2010-07
NCT00238030
2010-10
NCT00921050
2012-03
NCT01536678
2012-04
NCT01574859
2013-03
NCT00565890
2013-06
NCT04528797
2013-09-30
NCT01631305
2013-12
Q12
At the median, Levothyroxine's trials enrolled 61 people — anything larger?
Median enrolment
61
Largest enrolment
4657
Registered trials counted
125
Q13
What do 491 spontaneous reports say about Levothyroxine — and not say?
These are reports people sent to a regulator. They do not show the medicine caused the reaction. Nobody counted how many people took the medicine and reported nothing. The same event can be reported more than once, and many reports are incomplete. News coverage, lawsuits and new warnings change how often people report. A count is not a rate and not a risk.
Levothyroxine appears in spontaneous reports to regulators. Across the 10 most-reported reaction terms, 491 reaction mentions were counted: hyperthyroidism 75; abortion spontaneous 57; drug interaction 55; hypertension 55. open-targets-adr · CHEMBL1624 · 2026-06-24
Show the evidence
hyperthyroidism
75
abortion spontaneous
57
drug interaction
55
hypertension
55
palpitations
46
drug abuse
44
4 more recorded rows
hypothyroidism
44
premature baby
41
atrial fibrillation
39
blood thyroid stimulating hormone increased
35
recorded 2026-06-24 · last checked 2026-09-04
Q14
Was Levothyroxine studied with fasting?
fasting is named in Levothyroxine's label sentences: "We did a comprehensive search of 8 databases for Randomized controlled studies (RCTs) and observational studies investigating the effect of Ramadan fasting on thyroid functions in hypothyroid individuals taking levothyroxine." openfda-label+europepmc · 2023-09-21
1 recorded statement; fasting
Show the evidence
fasting
We did a comprehensive search of 8 databases for Randomized controlled studies (RCTs) and observational studies investigating the effect of Ramadan fasting on thyroid functions in hypothyroid individuals taking levothyroxine.
recorded 2023-09-21 · last checked 2026-09-04
Q15
What is recorded about Levothyroxine and mTOR?
"Inhibitors of mTOR or agents that restore SIRT1 could complement levothyroxine and antioxidant strategies." — where Levothyroxine and mTOR appear together. Europe PMC · pathway abstract search · 2026-04-13
mTOR, sirtuin, autophagy; PMID 41718108, 41982986
Show the evidence
mTORPMID 41718108
"Inhibitors of mTOR or agents that restore SIRT1 could complement levothyroxine and antioxidant strategies."
sirtuinPMID 41718108
"Inhibitors of mTOR or agents that restore SIRT1 could complement levothyroxine and antioxidant strategies."
autophagyPMID 41982986
"System-level and docking analyses support autophagy regulation as a key therapeutic mechanism, highlighting the potential role of levothyroxine in modulating autophagy."
recorded 2026-04-13 · last checked 2026-09-04
Where it is registeredIdentifiers, relations and other names
ClinicalTrials.gov — US Government work · Europe PMC — metadata only, under the recorded legal gate · Open Targets 26.06 — CC0 · derived from this page's own recorded fields; no external licence · mixed register set; per-register licences in docs/specs/corpus-20k-sources.md · openFDA / DailyMed — US Government work
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