This page shows what was measured, who it was measured in, and what that does not settle.
What Phentermine does in the body
Elsewhere it does what adrenaline does — raises heart rate, raises blood pressure, keeps you awake.
Phentermine makes nerve endings dump their stored noradrenaline into the synapse. In the part of the brain that regulates feeding, that suppresses appetite. It is structurally close to amphetamine and is a schedule IV controlled substance for that reason, though its abuse potential in practice is low.
Why people take it. A short-term prescription appetite suppressant
What happened in people
Composite cardiovascular disease or death in 0.3% of that cohort with no difference by duration of use
✎ 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 recorded finding that sits closest to something a person would notice. Written into the record, not signed off, and it carries no population or interval.
CONQUER — phentermine/topiramate in overweight and obese adults (NCT00553787) · a recorded source, not a stored snapshot
The limit that matters most
That sixty-five years of use without a randomised cardiovascular outcome trial establishes long-term cardiovascular safety for a sympathomimetic
Where it acts
Hypothalamic feeding centres and peripheral sympathetic nerve terminals
Kind of result
Living longer, or avoiding a major event
Supervision
Professional supervision is normally required. A regulator classifies this substance in a way that restricts how it is supplied.
What the registries record it as
The substance registry classes this as chemical.
FDA substance registry · C045TQL4WP · read 2026-08-29
Where each sentence above came from
A person wrote this explanation into the record, with the studies named in the path below.
The recorded use, written for a reader without medical training. Not signed off.
A limit recorded against this substance. Not signed off as a reviewed claim.
The four opening statements run to 85 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.
Placebo
A placebo is a dummy treatment given so the real one can be compared with it.
A picture of it, and where the picture fails
A placebo is like a blank control in an experiment.
Where that stops being true. A blank does nothing. People given a placebo often do get better.
What people get wrong. A placebo effect is read as imaginary. The improvement is measured and real.
An inactive intervention matched in appearance to the test intervention, used to control for non-specific effects.
Comparator
A comparator is whatever the treatment was measured against.
A picture of it, and where the picture fails
It is like the other runner in a race.
Where that stops being true. A race has one winner. A study can show both arms improved.
What people get wrong. Results are read without asking what the other group got. Beating nothing is not beating a treatment.
The control condition against which the experimental intervention is assessed.
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.
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 27 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
Body weight
∅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 moved9 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.
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.
Which registered measures put each goal on this table
Body weight
body weight from baseline to week 12; weight loss from baseline to week 28; at least 5 weight loss at week 28 locf; weight change; body weight at week 26; total body weight; body weight; weight loss
Energy
resting energy expenditure at low temperature
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.
△ Only a number moved
9 registered test measure.
— Not recorded
Harms were not a registered measure for this goal.
… Waiting for a reviewer
Who was studied is listed further down the page.
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.
Percentage change in bodyweight and proportion achieving at least 5% weight loss at 56 weeks
✓ The study showed what it set out to show
Who was studied
CONQUER (NCT00553787)
How many people
2487
Study design
Phase 3 randomised placebo-controlled trial of phentermine plus topiramate
Compared against
A dummy treatment
Kind of result
A number that stands in for health
What was found
-9.8% versus -1.2% on placebo for phentermine 15 mg plus topiramate 92 mg, P < 0.0001; 70% versus 21% achieving 5% loss, OR 9.0 (7.3 to 11.1)
Repeated elsewhere
Replicated
What this does not prove. Meeting one endpoint in one population does not carry to other goals or other people.
The limits of this study, and where it came from
Main limit. Paraesthesia rose to 21% and dysgeusia to 10% at the top dose, both attributable to topiramate. Topiramate is a first-trimester teratogen, which the fixed-dose product manages through pregnancy testing requirements rather than through the trial.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet, capsule, orally disintegrating tablet and resin complex, once daily
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
Percent weight loss at 6, 12 and 24 months, and composite cardiovascular disease or death up to three years, by duration of continuous phentermine use
✓ The study showed what it set out to show
Who was studied
Longer-term phentermine EHR cohort (Lewis et al.)
How many people
13972
Study design
Retrospective electronic health record cohort study
Compared against
Not recorded for this study
Kind of result
Living longer, or avoiding a major event
What was found
7.4% greater weight loss at 24 months for more than 12 months of use versus 3 months or less, P < 0.001; composite CVD or death 0.3% (41 events) with no significant hazard ratio difference between groups
Repeated elsewhere
Unreplicated
What this does not prove. Meeting one endpoint in one population does not carry to other goals or other people.
The limits of this study, and where it came from
Main limit. Observational design with no randomisation, so clinicians choosing to continue phentermine in healthier patients would produce this pattern in the absence of any true safety difference.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet, capsule, orally disintegrating tablet and resin complex, once daily
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
RNAWiki holds 2 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 eventNo evidence recorded. Death, a heart attack, a stroke, a hospital stay.No registered study measures this.
□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 lifeNo evidence recorded. Pain, tiredness, mood, sleep, as the person rated it.No registered study measures this.
■A number that stands in for healthEvidence recorded. Cholesterol, blood sugar, bone density. A stand-in, not the thing itself.11 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.
□AnimalsNo evidence recorded. Mice, rats, dogs. Useful for ideas, not proof about people.No animal record is stored.
□Cells in a dishNo evidence recorded. Cells or chemistry on a bench, far from a whole body.No cell or bench record is stored.
□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
Phentermine
What a person takes: Oral tablet, capsule, orally disintegrating tablet and resin complex, once daily.
The measurement behind this step
Taken in the morning as a short-term adjunct to a reduced-calorie diet. Largely renally excreted unchanged, with elimination markedly slowed by alkaline urine. Also formulated with extended-release topiramate in a once-daily fixed-dose capsule.
Getting in
A once-daily capsule or tablet, taken in the morning
Taken early in the day, because taken late it keeps people awake. Available as the hydrochloride and as a slower-releasing resin complex.
╌╌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 immediate-release tablets and capsules and an ion-exchange resin complex. Largely excreted unchanged in urine, with excretion rate dependent on urinary pH — alkaline urine slows elimination substantially.
CONQUER — phentermine/topiramate in overweight and obese adults (NCT00553787) · a recorded source, not a stored snapshot
Reaching the cell
Crosses into the brain and enters noradrenergic terminals
It passes into brain tissue and is carried inside the nerve endings that store noradrenaline.
╌╌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
Lipophilic and centrally penetrant. Transported into presynaptic terminals as a NET substrate rather than merely occupying the transporter, in the same way fenfluramine is a SERT substrate.
CONQUER — phentermine/topiramate in overweight and obese adults (NCT00553787) · a recorded source, not a stored snapshot
What it acts on
Reverses the noradrenaline transporter
Once inside, it makes the pump run backwards, so stored noradrenaline floods out into the synapse.
╌╌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
Disrupts vesicular storage and reverses NET, producing carrier-mediated noradrenaline efflux with weaker dopamine efflux. Serotonin release is negligible, and there is no meaningful 5-HT2B agonism — the pharmacological fact that separates it from fenfluramine.
CONQUER — phentermine/topiramate in overweight and obese adults (NCT00553787) · a recorded source, not a stored snapshot
The change it makes
Appetite falls, and sympathetic tone rises
In feeding circuits the effect is reduced hunger. Everywhere else it is the ordinary adrenaline effect: faster pulse, higher blood pressure, less sleep.
──Measured in people. Written by a person from the study named beside the step. Not signed off as a reviewed claim.
The measurement behind this step
Noradrenergic signalling in hypothalamic feeding centres suppresses energy intake. Peripheral sympathetic activation raises heart rate and blood pressure, which is why the label contraindicates use in patients with established cardiovascular disease and why it is not combined with monoamine oxidase inhibitors.
CONQUER — phentermine/topiramate in overweight and obese adults (NCT00553787) · a recorded source, not a stored snapshot
What that does for a person
Modest weight loss alone; substantial in combination
Alone the effect is modest and short-term. With topiramate it reaches about ten kilograms over a year.
──Measured in people. Written by a person from the study named beside the step. Not signed off as a reviewed claim.
The measurement behind this step
Measured endpoints: -10.2 kg versus -1.4 kg at 56 weeks for phentermine 15 mg plus topiramate 92 mg; 7.4% greater weight loss at 24 months for more than 12 months of monotherapy versus 3 months or less in an observational cohort; composite cardiovascular disease or death 0.3% across 13,972 patients with no difference by duration.
CONQUER — phentermine/topiramate in overweight and obese adults (NCT00553787) · a recorded source, not a stored snapshot
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.
No registered study measured anything of this kind.
Measured
Things only a test, a scale or a device shows.
body weight from baseline to week 12
weight loss from baseline to week 28
at least 5 weight loss at week 28 locf
weight change
body weight at week 26
total body weight
body weight
systolic blood pressure
weight loss
levels of lipids in circulation
and 1 more.
Meaningful
Things that change how a life goes, not only a number.
No registered study measured anything of this kind.
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 (16)
pharmacokinetic parameters
food intake
resting energy expenditure at low temperature
basal metabolic rate
brown adipose tissue activity
reinforcing effects
weight
maximum effect on drug liking visual analog scale
intrahepatic fat
enrollment rate
dropout rate
adherent to study drugs
frequency of adverse events
kidney stone size determined by non contrast cat scan
mdsc in peripheral blood
sf 36 physical component summary from baseline to 6 months
These are harms, study-process measures, or names the rules did not recognise. They are shown rather than dropped.
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.
Adults with obesity, as a short-term adjunct. It remains the most prescribed weight-loss drug in the United States by volume, and it is prescribed off-label for far longer than the licensed few weeks.
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: “Safety and effectiveness in pediatric patients have not been established.”
US prescribing information · 9155edf8-ea1d-458f-b2a7-e0303fd83cc0 · read 2026-08-30
On older people, the label states: “In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.”
US prescribing information · 9155edf8-ea1d-458f-b2a7-e0303fd83cc0 · read 2026-08-30
On people who are pregnant, the label states: “Teratogenic Effects Pregnancy category X Phentermine is contraindicated during pregnancy because weight loss offers no potential benefit to a pregnant woman and may result in fetal harm.”
US prescribing information · 9155edf8-ea1d-458f-b2a7-e0303fd83cc0 · read 2026-08-30
On people who are breastfeeding, the label states: “It is not known if phentermine is excreted in human milk; however, other amphetamines are present in human milk.”
US prescribing information · 9155edf8-ea1d-458f-b2a7-e0303fd83cc0 · read 2026-08-30
On people with reduced kidney function, the label states: “Based on the reported excretion of phentermine in urine, exposure increases can be expected in patients with renal impairment [see Clinical Pharmacology ( 12.3 )].”
US prescribing information · 9155edf8-ea1d-458f-b2a7-e0303fd83cc0 · read 2026-08-30
Where the result stopped carrying
The unapproved fen-phen combination was assembled in practice from two separately approved drugs and caused valvular heart disease; only the fenfluramine half was withdrawn
The licensed indication remains short-term use, a limitation that has never been reconciled with how the drug is actually prescribed
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.
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 (10)
A different form was studied
The studied form is not the form on the shelf. Nothing in this record points to this reason.
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
Withdrawn
❝ 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, capsule, orally disintegrating tablet and resin complex, once daily
✎ 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
Professional supervision is normally required. A regulator classifies this substance in a way that restricts how it is supplied.
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
Suppression classes recorded: S3, S8.
No source is stored against this line.
What is in the pack
Taken in the morning as a short-term adjunct to a reduced-calorie diet. Largely renally excreted unchanged, with elimination markedly slowed by alkaline urine. Also formulated with extended-release topiramate in a once-daily fixed-dose capsule.
✎ 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
Schedule IV controlled substance. Sympathomimetic effects — raised heart rate, raised blood pressure, insomnia, dry mouth — are the expected pharmacology rather than idiosyncratic reactions, and the label contraindicates use in established cardiovascular disease and with monoamine oxidase inhibitors. It does not carry fenfluramine's valvular signal: the population study that measured it found zero idiopathic valvular disorders among phentermine-only users. The combination product adds topiramate's first-trimester teratogenicity and its own pregnancy-testing requirements.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
CONQUER — phentermine/topiramate in overweight and obese adults (NCT00553787) · a recorded source, not a stored snapshot
Reports sent to a regulator
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.
Phentermine appears in spontaneous reports to regulators. Across the 10 most-reported reaction terms, 275 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, capsule, orally disintegrating tablet and resin complex, once daily
✎ 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
Largely renally excreted unchanged, with elimination markedly slowed by alkaline urine. Also formulated with extended-release topiramate in a once-daily fixed-dose capsule.
✎ 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
164 products list this as an active ingredient in the United States drug directory. 136 of them contain it and nothing else.
FDA National Drug Code directory · 0480-2299 · read 2026-08-29
They are sold as capsule, capsule, extended release, liquid, powder and tablet, taken oral.
FDA National Drug Code directory · 0480-2299 · read 2026-08-29
The regulator's established pharmacologic class for it is appetite suppression [pe], increased sympathetic activity [pe] and sympathomimetic amine anorectic [epc].
FDA National Drug Code directory · 0480-2299 · read 2026-08-29
116 published labels name it as an active ingredient. 112 of them describe this substance alone, which is where its own label text on this page comes from.
US prescribing information · 9155edf8-ea1d-458f-b2a7-e0303fd83cc0 · read 2026-08-29
Those labels are classed as human prescription drug.
US prescribing information · 9155edf8-ea1d-458f-b2a7-e0303fd83cc0 · read 2026-08-29
Phentermine hydrochloride is oral at 3 DOSAGE FORMS AND STRENGTHS Capsules containing 37.5 mg phentermine hydrochloride (equivalent to 30 mg phentermine base)., recorded as fda label in effect 2026-03-16 in the United States.
US prescribing information · 9155edf8-ea1d-458f-b2a7-e0303fd83cc0 · read 2026-08-30
Recorded price in US: 0.07085–0.61598 USD per one unit as the pricing file counts it — a tablet, capsule, patch or single item, across 32 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.
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.
Self-experiment planning is not offered for a prescription or clinician-supervised medicine, withdrawn medicine. The questions below are for a clinician or pharmacist.
Questions worth asking
Which of the trials of Phentermine 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.
RNAWiki records evidence. It does not say whether this substance is right for you.
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 sixty-five years of use without a randomised cardiovascular outcome trial establishes long-term cardiovascular safety for a sympathomimetic
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 an observational finding of no excess events with longer use is equivalent to a randomised safety result, when clinicians choose who continues treatment
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 1998 phentermine valvular result excludes a small effect — 862 users give a 95% confidence interval reaching 76.6 per 10,000
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.
How fast does the body clear it?
The sources RNAWiki checked hold nothing for this field.
Why it matters. Without this, nothing on this page can say how long anything lasts.
What would answer it
A stored source that records 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 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 Phentermine 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.
Zero idiopathic valvular disorders among phentermine-only users
In plain words
In the population study that established the valve risk of fen-phen, nobody who took phentermine alone developed valve disease. The rate was the same as in people who took no appetite suppressant at all.
What was measured
Five-year cumulative incidence of idiopathic valvular disorders per 10,000, by drug
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Population-based follow-up with nested case-control analysis: 862 subjects on phentermine, 6,532 on dexfenfluramine, 2,371 on fenfluramine, and 9,281 obese controls matched for age, sex and weight, all free of diagnosed cardiovascular disease at baseline, mean follow-up about four years. Of 11 newly diagnosed idiopathic valvular disorders, none occurred among phentermine-only users and none among untreated controls. Five-year cumulative incidence per 10,000 was 0 for phentermine alone (95% CI 0 to 76.6) and 0 for untreated controls (95% CI 0 to 15.4), against 35.0 (16.4 to 76.2) for four or more months of fenfluramine or dexfenfluramine. The wide confidence interval on the phentermine estimate is the honest caveat: 862 users cannot exclude a small effect, only a large one.
Written into the record, not signed off as a reviewed claim
CONQUER: with topiramate, 10.2 kg lost at 56 weeks against 1.4 kg on placebo
In plain words
Combined with a low dose of an anticonvulsant, phentermine produced about ten kilograms of weight loss in a year. Seven in ten patients lost at least 5% of their body weight; two in ten did on placebo.
What was measured
Percentage change in bodyweight at 56 weeks and proportion losing 5% or more
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
56-week phase 3 trial in 93 US centres, 2,487 overweight or obese adults aged 18 to 70 with BMI 27 to 45 kg/m2 and two or more comorbidities, randomised 2:1:2 to placebo (n=994), phentermine 7.5 mg plus topiramate 46.0 mg (n=498), or phentermine 15.0 mg plus topiramate 92.0 mg (n=995). At 56 weeks, weight change was -1.4 kg on placebo (least-squares mean -1.2%), -8.1 kg (-7.8%, p<0.0001) on the lower dose and -10.2 kg (-9.8%, p<0.0001) on the higher. At least 5% weight loss was achieved by 21%, 62% (OR 6.3, 95% CI 4.9 to 8.0) and 70% (OR 9.0, 7.3 to 11.1); at least 10% by 7%, 37% and 48%. Commonest adverse events were dry mouth (2%, 13%, 21%), paraesthesia (2%, 14%, 21%), constipation, insomnia, dizziness and dysgeusia, all dose-related.
Written into the record, not signed off as a reviewed claim
A 13,972-patient cohort found more weight loss with longer use and no excess events
In plain words
Following nearly fourteen thousand patients for up to three years, people who stayed on phentermine longer lost more weight, and heart events and deaths were no more common than in short-term users.
What was measured
Percent weight loss at 24 months and composite cardiovascular disease or death by duration of use
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Electronic health record cohort of 13,972 adults with a first phentermine fill between 2010 and 2015, categorised by duration of continuous use with three months or less as referent. The cohort was 84% female and 45% white, mean baseline age 43.5 years (SD 10.7) and BMI 37.8 kg/m2 (SD 7.2). In multivariable models, patients using continuously for more than 12 months lost 7.4% more weight than the referent group at 24 months (p<0.001). The composite of cardiovascular disease or death was rare — 0.3%, 41 events — with no significant difference in hazard ratios between duration groups over up to three years. The authors state the limitation themselves: this is observational, so channelling of healthier patients to longer treatment cannot be excluded.
Written into the record, not signed off as a reviewed claim
Licensed for a few weeks, prescribed for years, tested for neither
In plain words
The label says short-term use. Real prescribing runs for months or years. The evidence for that longer use is a database study, not a randomised trial.
What was measured
That decades of widespread long-term use, without a randomised cardiovascular outcome trial, establish long-term cardiovascular safety
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Phentermine has been licensed since 1959 as a short-term adjunct, a limitation dating from an era when obesity was not treated as a chronic disease. Actual practice diverged, which is why the 13,972-patient cohort study exists at all. That study supports effectiveness and safety of longer-term use in low-risk individuals, and its own authors qualify it as observational. What does not exist for phentermine monotherapy, after sixty-five years, is a randomised cardiovascular outcome trial. Given that the drug is a sympathomimetic that raises heart rate and blood pressure, and that sibutramine — a different monoamine drug in the same indication — failed exactly that trial, the absence is worth stating rather than glossing.
Written into the record, not signed off as a reviewed claim
Fen-phen was blamed on both drugs. The mechanism convicted only one
In plain words
When fen-phen was withdrawn, both components were under suspicion. Working out the receptor responsible cleared phentermine, which is why it is still prescribed today.
What was measured
Not recorded
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The valvular lesion in fen-phen users was histopathologically identical to carcinoid and ergotamine valve disease, which pointed at 5-HT2B agonism on cardiac valve interstitial cells. Fenfluramine's metabolite norfenfluramine is a potent 5-HT2B agonist; phentermine releases noradrenaline with negligible serotonin release and no meaningful 5-HT2B activity. The epidemiology matched the mechanism exactly: zero idiopathic valvular disorders among phentermine-only users. Only fenfluramine and dexfenfluramine were withdrawn on 15 September 1997. Phentermine kept its licence, and in 2012 the FDA approved it as half of a new fixed-dose combination — fifteen years after the episode that made its name notorious.
Written into the record, not signed off as a reviewed claim
The combination adds a teratogen, and the label handles that explicitly
In plain words
Adding topiramate roughly triples the weight loss and also adds a drug known to cause birth defects, so the combination product comes with pregnancy testing requirements phentermine alone does not have.
What was measured
Dose-related incidence of paraesthesia and dysgeusia in CONQUER
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Topiramate exposure in the first trimester is associated with oral clefts, which is why QSYMIA carries pregnancy-related contraindications and requirements that phentermine monotherapy does not. The dose-related adverse events measured in CONQUER are consistent with the topiramate contribution: paraesthesia rose from 2% on placebo to 14% and 21% across the two combination doses, and dysgeusia from 1% to 7% and 10%. The trade in the combination product is therefore not simply "more weight loss" — it is more weight loss plus a distinct reproductive-safety obligation, and the two have to be read together.
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What is not here
4 questions this page could not answer
These sections were prepared and left out because there was nothing to put in them. They are listed rather than hidden, so the gaps in this record are visible.
How long anything takes — found nothing in the sources checked.
What it may clash with — found nothing in the sources checked.
Other ways to the same goal — found nothing in the sources checked.
What changed on this page — found nothing in the sources checked.
The record as stored
The full record, for auditing
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.
A noradrenaline releasing agent that produced zero cases of idiopathic valvular disease in the population study that condemned its fen-phen partner, and that after sixty-five years on the market still has no cardiovascular outcome trial of its own.
Recorded evidence blocks (10)
Q2
What did Phentermine's largest trial (870 people) and its longest (10 years) measure?
870 people in Phentermine's largest registered study, 10 years in its longest registered window, measuring All treatment-emergent adverse events occurring during the 24-week treatment period. ClinicalTrials.gov · 2026-09-01
10 phase4, 8 phase2, 5 phase1, 2 na, 2 phase3, 1 early phase1, 1 na or unstated; NCT01950520; 2024-06-11; no ageing endpoint recorded. Last human test completed 2024, NCT04621929.
Interpretation These counts include studies where Phentermine 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
10
phase2
8
phase1
5
na
2
phase3
2
early phase1
1
2 more recorded rows
na or unstated
1
Last recorded human testNCT04621929
2024-11-14
recorded 2026-09-01 · last checked 2026-09-04
Q3
Phentermine was tested only in human — what did it show?
5 recorded entries; human; also "Phentermine 45 mg", "Phentermine 15 MG", "Phentermine 37.5 Mg"
Show the evidence
human
NCT02609477
Phentermine 45 mg
NCT02911818
Phentermine 15 MG
NCT04614545
Phentermine 37.5 Mg
NCT05176626
Phentermine Hydrochloride 8 MG
NCT06768320
Lomaira 8Mg Tablet
recorded 2026-09-01 · last checked 2026-09-04
Q6
Which of adherent to study drugs, at least 5 weight loss at week 28 locf and basal metabolic rate did Phentermine's trials measure?
adherent to study drugs, at least 5 weight loss at week 28 locf and basal metabolic rate lead 27 outcome terms across Phentermine's trials. ClinicalTrials.gov · 2026-09-01
at least 5 weight loss at week 28 locf, weight change, food intake, resting energy expenditure at low temperature, basal metabolic rate and brown adipose tissue activity follow.
Show the evidence
body weight from baseline to week 12
1
pharmacokinetic parameters
1
weight loss from baseline to week 28
1
at least 5 weight loss at week 28 locf
1
weight change
1
food intake
1
14 more recorded rows
resting energy expenditure at low temperature
1
basal metabolic rate
1
brown adipose tissue activity
1
reinforcing effects
1
body weight at week 26
1
weight
1
maximum effect on drug liking visual analog scale
1
total body weight
1
intrahepatic fat
1
enrollment rate
1
dropout rate
1
adherent to study drugs
1
frequency of adverse events
1
body weight
1
recorded 2026-09-01 · last checked 2026-09-04
Q7
Which of Phentermine's 5 ongoing trials reports first?
Change in body weight (%); weight loss; latest 2034-02-01
Show the evidence
Trial
NCT05176626
"Long-term Effectiveness of the Antiobesity Medication Phentermine"; n 870; "Change in body weight (%)"; 2026-12-31
NCT05756764
"Anti-obesity Pharmacotherapy and Inflammation"; n 30; "weight loss"; 2026-02-20
NCT05975580
"Pharmacotherapy in Conjunction With Lifestyle Counseling for Management of Weight Regain After Bariatric Surgery"; n 120; "Percent weight loss at Month 12 - Topiramate vs placebo"; 2028-01-31
NCT07058155
"Optimizing Portal Hypertension With TIPS and Interval Metabolic Surgery for Advanced Liver Disease"; n 70; "Change in SF-36 Physical Component Summary (PCS) Score From Baseline to 6 Months"; 2034-02-01
NCT07282340
"Phentermine's Impact on Treatment in Teens"; n 240; "Percent Change in BMI from Baseline at Week 52"; 2028-01
recorded 2026-09-01 · last checked 2026-09-04
Q8
Which 8 trials of Phentermine posted no result?
Posted no result
8 of 8 completed trials
Registrations
NCT00000506, NCT00402077, NCT00518466, NCT01719185, NCT02609477 and NCT03152123, and 2 more
Completion dates
oldest 1988-04; newest 2020-04-01
Show the evidence
Trial
NCT00000506
1988-04
NCT00402077
2007-08
NCT00518466
2007-12
NCT01719185
2013-04
NCT02609477
2016-07
NCT03152123
2017-10-23
2 further recorded trials
NCT02239913
2019-09
NCT03849729
2020-04-01
Q9
At the median, Phentermine's trials enrolled 55.5 people — anything larger?
Median enrolment
55.5
Largest enrolment
870
Registered trials counted
28
Q10
What do 275 spontaneous reports say about Phentermine — 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.
Phentermine appears in spontaneous reports to regulators. Across the 10 most-reported reaction terms, 275 reaction mentions were counted: hypertension 41; angle closure glaucoma 31; pregnancy 31; palpitations 30. open-targets-adr · CHEMBL1200912 · 2026-06-24
Show the evidence
hypertension
41
angle closure glaucoma
31
pregnancy
31
palpitations
30
paraesthesia
30
arteriospasm coronary
26
4 more recorded rows
alopecia
25
atrial fibrillation
24
acute myocardial infarction
19
stress cardiomyopathy
18
recorded 2026-06-24 · last checked 2026-09-04
Q11
Was Phentermine studied with caloric restriction and exercise?
caloric restriction and exercise are named in Phentermine's label sentences: "To investigate the value of anorexiant medications as an adjunct to other forms of weight control therapy, we studied 121 people in a 34-week, double-blind clinical trial of 60 mg extended-release fenfluramine plus 15 mg phentermine resin versus placebo added to behavior modification, caloric…" openfda-label+europepmc · 2014-04-01
2 recorded statements; caloric restriction, exercise
Show the evidence
caloric restriction
To investigate the value of anorexiant medications as an adjunct to other forms of weight control therapy, we studied 121 people in a 34-week, double-blind clinical trial of 60 mg extended-release fenfluramine plus 15 mg phentermine resin versus placebo added to behavior modification, caloric restriction, and exercise.
exercise
The approvals were based on 1-year trials showing that on top of recommendations to follow a calorie-restricted diet and to increase exercise, patients randomized to either drug lost more weight than patients randomized to placebo (3% [95% CI, 3%-4%] more weight lost with lorcaserin; 7% [95% CI, 3%-4%] more with phentermine /topiramate).
recorded 2014-04-01 · 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
✗ required summary fields resolved: 5 required field(s) not terminal: Why people use it, Best-supported result, Most important common problem, Biggest unanswered question, Human evidence
✓ public claims reviewed: 0 reviewed claim(s); drafts are never rendered
✓ source coverage passed: 8 source rows
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This is a record of evidence. It is not medical advice, and it does not say this substance suits you. Nothing here says any substance on RNAWiki is appropriate for a child.