This page shows what was measured, who it was measured in, and what that does not settle.
What Doxycycline Anhydrous does in the body
Nothing can dock, the chain stops growing, and the bacterium stops multiplying.
To build a protein, a bacterium has to bring in amino acids one at a time and dock each one into a slot on the ribosome. Doxycycline sits in that slot. It gets inside human cells easily, which is why it reaches bacteria that live there and most other cheap antibiotics do not.
Why people take it. Tick-borne and sexually transmitted infections, chest infections, acne, and malaria prevention
What happened in people
Relative risk 0.34 for any bacterial sexually transmitted infection per quarter in the DoxyPEP pre-exposure-prophylaxis cohort, and 0.38 in the cohort living with HIV
✎ 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.
That an efficacy result in one population transfers unchanged to a different population, different anatomical sites of infection and different adherence
Where it acts
Bacterial 30S ribosome, including organisms living inside human cells
Kind of result
The kind of result is not recorded
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
Its recorded molecular formula is C22H24N2O8•H2O, weighing 462.45.
US prescribing information · 81c5a7fc-3fe0-40b2-bae0-c79eb0b27697 · read 2026-08-30
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 102 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.
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.
Absolute difference
An absolute difference is how many more people in a hundred were affected.
A picture of it, and where the picture fails
It is like counting heads in two rooms of a hundred.
Where that stops being true. Heads are easy to count. Study results carry a margin of error too.
What people get wrong. It is confused with a percentage change, which can look far larger.
The arithmetic difference in event rates between arms.
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.
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.
Incidence of at least one bacterial sexually transmitted infection per follow-up quarter
✓ The study showed what it set out to show
Who was studied
DoxyPEP (NCT03980223)
How many people
501
Study design
Phase 4 randomised open-label
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
P < 0.001 in both cohorts (relative risk 0.34 and 0.38)
Repeated elsewhere
Failed to Replicate
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. Tetracycline-resistant gonorrhoea was recovered from 5 of 13 cultured participants in the doxycycline groups versus 2 of 16 in standard care.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral capsule, tablet, delayed-release tablet, oral suspension and intravenous infusion
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
Incident chlamydia, gonorrhoea or syphilis in cisgender women over 12 months
✗ The study did not show it
Who was studied
dPEP Kenya (NCT04050540)
How many people
449
Study design
Phase 4 randomised open-label
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
P = 0.51 (relative risk 0.88, 95% CI 0.60 to 1.29)
Repeated elsewhere
Failed to Replicate
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. Hair testing detected doxycycline in only 29.0% of samples from the intervention arm, so the trial measures the strategy as delivered rather than the drug as taken.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral capsule, tablet, delayed-release tablet, oral suspension and intravenous infusion
Interval reported. 95% CI 0
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 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
Doxycycline Anhydrous
What a person takes: Oral capsule, tablet, delayed-release tablet, oral suspension and intravenous infusion.
The measurement behind this step
Usually 100 mg once or twice daily by mouth. Absorption is high and only modestly food-affected, but divalent and trivalent cations in dairy, antacids and iron supplements chelate the drug in the gut and reduce absorption. Delayed-release and subantimicrobial-dose formulations exist for dermatological use.
Getting in
Absorbed almost completely and distributed into tissue
Doxycycline is absorbed better than older tetracyclines and reaches most tissues, including places bacteria hide.
╌╌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 bioavailability is high and largely unaffected by food, unlike tetracycline itself. The 6-alpha-methyl, 6-deoxy configuration gives a long elimination half-life, so twice-daily and then once-daily dosing is possible. Elimination is substantially non-renal, which is why it is usable in renal impairment.
Carried into the bacterium, and into human cells too
The drug is lipid-soluble enough to cross into human cells, which is how it reaches bacteria that live inside them.
╌╌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
Entry into Gram-negative bacteria is through OmpF and OmpC porins as a magnesium chelate, followed by energy-dependent transport across the inner membrane. High lipophilicity also allows passive entry into mammalian cells, which is the basis of activity against Rickettsia, Chlamydia and Coxiella.
It occupies the docking slot on the small ribosomal subunit
The drug sits in the slot where the next amino acid has to arrive.
╌╌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
Doxycycline binds the h34 region of 16S ribosomal RNA in the 30S subunit, overlapping the aminoacyl-tRNA acceptor site. A single high-affinity primary site accounts for the antibacterial effect; the interaction is reversible.
With the slot occupied, the protein chain cannot be extended.
╌╌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
Aminoacyl-tRNA delivery to the A site is sterically blocked, halting elongation. The effect is bacteriostatic and reversible on drug removal, which is why treatment duration and adherence matter more here than with a bactericidal beta-lactam.
The infection is controlled, while bacteria carrying pump or protection genes gain an advantage.
──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
Resistance is mediated by tet efflux pumps and by ribosomal protection proteins such as TetM. Both DoxyPEP and the Kenyan dPEP trial recovered tetracycline-resistant gonococci from treated participants, which is the measured version of this step rather than a theoretical one.
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 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.
People with tick-borne infection, chlamydial infection, atypical pneumonia, moderate acne or rosacea, travellers taking malaria prophylaxis, and men who have sex with men and transgender women taking post-exposure prophylaxis against bacterial sexually transmitted infections.
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: “Doxycycline capsules should not be used in infants and children less than 8 years of age [ see Warnings and Precautions ( 5.1 ) ].”
US prescribing information · 81c5a7fc-3fe0-40b2-bae0-c79eb0b27697 · read 2026-08-30
On older people, the label states: “Clinical studies of doxycycline capsules did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects.”
US prescribing information · 81c5a7fc-3fe0-40b2-bae0-c79eb0b27697 · read 2026-08-30
On people who are pregnant, the label states: “Risk Summary Doxycycline may cause reversible inhibition of bone growth and permanent discoloration of deciduous teeth when administered during the second and third trimesters of pregnancy [ see Warnings and Precautions ( 5.1 and 5.2 ) ].”
US prescribing information · 81c5a7fc-3fe0-40b2-bae0-c79eb0b27697 · read 2026-08-30
On people who are breastfeeding, the label states: “Risk Summary Based on available published data, doxycycline is likely to be present in human breast milk but the specific concentration in breastmilk is not clear.”
US prescribing information · 81c5a7fc-3fe0-40b2-bae0-c79eb0b27697 · read 2026-08-30
Where the result stopped carrying
N-TA3CT: no effect on aneurysm growth despite a plausible and well-characterised mechanism
PRINCIPLE: the doxycycline arm was stopped for futility in community COVID-19
dPEP Kenya: no significant reduction in sexually transmitted infections in cisgender women
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 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.
The product may not be what it says
Contents of a sold product are not always what the label states.
On this record: This is sold as a supplement, so no agency checked what is in a given tub before it was sold.
Other reasons RNAWiki checked and found nothing for (10)
It was studied for a different goal
The studies measured something else entirely. Nothing in this record points to this reason.
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.
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 capsule, tablet, delayed-release tablet, oral suspension and intravenous infusion
✎ 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.
No source is stored against this line.
What is in the pack
Usually 100 mg once or twice daily by mouth. Absorption is high and only modestly food-affected, but divalent and trivalent cations in dairy, antacids and iron supplements chelate the drug in the gut and reduce absorption. Delayed-release and subantimicrobial-dose formulations exist for dermatological 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.
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
Photosensitivity is common and predictable. Pill-induced oesophagitis occurs when a dose is taken without enough water or lying down. Tetracyclines are avoided in children under eight and in pregnancy because of effects on developing teeth and bone. Clostridioides difficile infection is a recognised complication of any broad-spectrum antibacterial course. Intracranial hypertension is a rare but documented class effect.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
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 capsule, tablet, delayed-release tablet, oral suspension and intravenous infusion
✎ 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
Absorption is high and only modestly food-affected, but divalent and trivalent cations in dairy, antacids and iron supplements chelate the drug in the gut and reduce absorption. Delayed-release and subantimicrobial-dose formulations exist for dermatological 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.
Recorded notes on which forms are sold and how they compare.
No source is stored against this line.
What is recorded as being sold
353 products list this as an active ingredient in the United States drug directory. 353 of them contain it and nothing else.
FDA National Drug Code directory · 72162-2402 · read 2026-08-29
They are sold as capsule, capsule, delayed release, for suspension, injection, powder, for solution, injection, powder, lyophilized, for solution and paste, taken intravenous and oral.
FDA National Drug Code directory · 72162-2402 · read 2026-08-29
The regulator's established pharmacologic class for it is tetracycline-class drug [epc] and tetracyclines [cs].
FDA National Drug Code directory · 72162-2402 · read 2026-08-29
240 published labels name it as an active ingredient. 240 of them describe this substance alone, which is where its own label text on this page comes from.
US prescribing information · 5fdc01c3-c62f-40cf-8351-91cbcc43d379 · read 2026-08-29
Those labels are classed as human prescription drug.
US prescribing information · 5fdc01c3-c62f-40cf-8351-91cbcc43d379 · read 2026-08-29
1 marketed supplement label lists this ingredient, classed as other combinations.
Those labels carry all other, nutrient and structure/function claims. A claim of that kind is written by the manufacturer and is not assessed by any regulator, so its presence says nothing about whether it is true.
Doxycycline Hyclate Capsules, USP is capsules at Each capsule contains doxycycline hyclate equivalent to 100 mg doxycycline, recorded as prescription product; fda label in effect 2026-05-01 in the United States.
US prescribing information · 00b2aa98-dea2-90c3-e063-6294a90a35d6 · read 2026-08-27
Recorded price in US: 0.09836–5.15813 USD per one unit as the pricing file counts it — a tablet, capsule, patch or single item, across 84 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
Recorded price in US: 0.2288 USD per one millilitre, across 3 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. The questions below are for a clinician or pharmacist.
Questions worth asking
Which of the trials of Doxycycline Anhydrous 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 an efficacy result in one population transfers unchanged to a different population, different anatomical sites of infection and different adherence
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 inhibiting matrix metalloproteinases in the laboratory would slow aneurysm growth in patients — tested directly and refuted
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 prophylaxis can be scaled without a corresponding rise in tetracycline resistance, when both trials recovered resistant gonococci from treated participants
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 Doxycycline Anhydrous 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.
Taking a single 200 mg dose within 72 hours of condomless sex cut the combined rate of gonorrhoea, chlamydia and syphilis by about two thirds in two cohorts.
What was measured
Incidence of at least one bacterial sexually transmitted infection per follow-up quarter
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Open-label randomised trial, 501 participants in two cohorts: men who have sex with men and transgender women taking HIV pre-exposure prophylaxis, and people living with HIV, all with a bacterial sexually transmitted infection in the past year. In the PrEP cohort an infection was diagnosed at 10.7% of quarterly visits on doxycycline versus 31.9% on standard care, relative risk 0.34 (95% CI 0.24 to 0.46; P<0.001). In the cohort living with HIV, 11.8% versus 30.5%, relative risk 0.38 (95% CI 0.24 to 0.60; P<0.001). Chlamydia showed the largest effect, relative risk 0.12 in the PrEP cohort.
Written into the record, not signed off as a reviewed claim
dPEP Kenya: the same intervention showed no significant effect in cisgender women
In plain words
When the same strategy was tested in 449 Kenyan women, the infection rate did not fall significantly, and hair testing showed most participants were not actually taking the drug.
What was measured
Incident Chlamydia trachomatis, Neisseria gonorrhoeae or Treponema pallidum infection
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
Randomised open-label trial in Kenyan women aged 18 to 30 receiving HIV pre-exposure prophylaxis, followed quarterly for 12 months. 109 incident infections occurred, 50 in the doxycycline arm (25.1 per 100 person-years) and 59 in standard care (29.0 per 100 person-years), relative risk 0.88 (95% CI 0.60 to 1.29; P=0.51). Chlamydia accounted for 78% of infections. Objective adherence measurement mattered: doxycycline was detected in only 58 of 200 hair samples (29.0%) from 50 randomly selected participants in the intervention arm. Every gonococcal isolate recovered was doxycycline-resistant.
Written into the record, not signed off as a reviewed claim
The prophylaxis benefit was measured alongside tetracycline-resistant gonorrhoea
In plain words
In the trial that showed the benefit, resistant gonorrhoea was found in more of the treated participants than the untreated ones.
What was measured
That the individual-level reduction in infections can be scaled to a population without a corresponding rise in tetracycline resistance
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Among DoxyPEP participants with a gonococcal culture available, tetracycline-resistant Neisseria gonorrhoeae was recovered from 5 of 13 in the doxycycline groups and 2 of 16 in the standard-care groups. In the Kenyan dPEP trial, all gonococcal isolates recovered were doxycycline-resistant. These are small numbers from culture subsets, not powered resistance endpoints, which is exactly why the population-level consequence of the strategy remains an open question rather than a settled one.
Written into the record, not signed off as a reviewed claim
N-TA3CT: no effect on abdominal aortic aneurysm growth
In plain words
Doxycycline inhibits the enzymes that break down connective tissue, so it was tested to slow aneurysm growth. Two years of treatment changed nothing.
What was measured
Change in maximum transverse aneurysm diameter on CT at 2 years
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
Randomised, placebo-controlled trial at 22 US centres in 261 patients aged 50 and over with small infrarenal aneurysms. Doxycycline 100 mg twice daily for 2 years versus placebo. The change in measured maximum transverse diameter at 2 years was 0.36 cm (95% CI 0.31 to 0.40) with doxycycline and 0.36 cm (95% CI 0.30 to 0.41) with placebo, difference 0.0 cm (95% CI -0.07 to 0.07; P=0.93). The primary normal-scores analysis gave a one-sided P of 0.71. Joint pain occurred in 65% and 63%.
Written into the record, not signed off as a reviewed claim
PRINCIPLE: no benefit in community COVID-19, and the arm was stopped for futility
In plain words
Doxycycline was widely prescribed for COVID-19 in the community. When it was finally tested, the trial arm was stopped because it was clearly not working.
What was measured
Time to first self-reported recovery, and hospitalisation or death by day 28
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
UK primary-care adaptive platform trial in people aged 65 and over, or 50 and over with comorbidities. 2,689 participants were randomised to the doxycycline comparison between July and December 2020, when the prespecified futility criterion was met. Median time to first self-reported recovery was 9.6 days with doxycycline and 10.1 days with usual care, hazard ratio 1.04 (95% Bayesian credible interval 0.93 to 1.17), with a 0.10 probability of a clinically meaningful benefit. Hospitalisation or death occurred in 5.3% and 4.5%.
Written into the record, not signed off as a reviewed claim
A 1967 antibiotic acquired a genuinely new indication in 2023
In plain words
Doxycycline has been in use since the Johnson administration. Post-exposure prophylaxis for sexually transmitted infections is a new use, established by a randomised trial fifty-six years later.
What was measured
Not recorded
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Vibramycin was approved in the United States in December 1967. The DoxyPEP randomised trial reported in 2023 and changed clinical guidance for a defined population within months, on a relative risk of 0.34 in the PrEP cohort. That the dPEP trial in Kenyan women published later the same year found no significant effect is the reason the guidance is written for specific populations rather than for everyone.
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What is not here
7 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.
What was measured, goal by goal — found nothing in the sources checked.
How close this is to real life — found nothing in the sources checked.
Felt, measured, or meaningful — found nothing in the sources checked.
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 tetracycline that blocks the bacterial ribosome docking site, which cut the combined incidence of gonorrhoea, chlamydia and syphilis by about two thirds in 501 men who have sex with men and transgender women, and showed no significant effect in 449 Kenyan cisgender women in the direct replication attempt.
Recorded evidence blocks (10)
Q2
On the Doxycycline Anhydrous label: indicated for what?
"Doxycycline hyclate delayed-release tablets are a tetracycline-class drug indicated for: • Rickettsial infections (1.1) • Sexually transmitted infections (1.2) • Respiratory tract infections (1.3) • Specific bacterial infections (1.4) • Ophthalmic infections (1.5) • Anthrax, including inhalational anthrax…": indications and usage on Doxycycline Anhydrous's label. DailyMed label · 3ae4ca12-be39-46b9-bc4c-f8356776c175 · 2026-04-28
Q3
275 registered trials of Doxycycline Anhydrous — at which phases?
Registered studies posting no result
200 of 275
275 registered studies of Doxycycline Anhydrous: 78 phase2, 78 phase4, 48 na, 46 phase3, 28 phase1, 7 na or unstated, 5 early phase1. CLINICALTRIALS_SNAPSHOT · 2026-09-01
1195 with a PubMed record
Show the evidence
phase2
78
phase4
78
na
48
phase3
46
phase1
28
na or unstated
7
9 more recorded rows
early phase1
5
completed
165
unknown
40
recruiting
22
terminated
18
withdrawn
12
active not recruiting
9
not yet recruiting
8
enrolling by invitation
1
recorded 2026-09-01 · last checked 2026-09-04
Q4
29 of Doxycycline Anhydrous's trials stopped: futility/efficacy, accrual/recruitment, funding/business, other?
futility/efficacy (1), accrual/recruitment (14), funding/business (2) and other (12): Doxycycline Anhydrous's stop wording, clustered. CLINICALTRIALS_SNAPSHOT · 2026-09-01
"Investigator left the institution and decided not to continue with the study."; 29 of 275 registered studies
Show the evidence
Trial
NCT00803842
withdrawn; "Investigator left the institution and decided not to continue with the study."
NCT00952861
withdrawn; "Stopped due to poor recruitment"
NCT01014260
withdrawn; "We could not get funding for study."
NCT01030666
terminated; "shelf life of investigational drug ran out before 90 patients could be included"
NCT01188954
withdrawn; "The recruitment process was slower than expected."
NCT01317433
terminated; "The study stopped due to a lack of recruitment"
14 further recorded trials
NCT01590082
terminated; "Accrual slow due to alternate trials and treatment options."
NCT01653522
withdrawn; "No participants enrolled"
NCT01879930
terminated; "Recruitment problems"
NCT01935622
terminated; "End of funding"
NCT02086591
terminated; "Lack of accrual"
NCT02099240
terminated; "Not enough patient enrollment and lack of staffing"
NCT02201381
withdrawn; "Prospective recruitment not possible"
NCT02341209
terminated; "Low enrollment"
NCT02388477
withdrawn; "Research idea tabled at this point."
NCT02569437
terminated; "A high percentage of patients were dropping out of the study and were not able to complete the protocol."
NCT02623959
terminated; "Slow Accrual"
NCT02874430
terminated; "study closed early due to slow accrual"
NCT03076281
terminated; "Insufficient staff to conduct the trial"
NCT03173053
terminated; "Results interim-analysis"
recorded 2026-09-01 · last checked 2026-09-04
Q5
Human studies of Doxycycline Anhydrous used 20 mg doxycycline hyclate — over how long?
studies of Doxycycline Anhydrous used the recorded amount. ClinicalTrials.gov · 2026-09-01
20 recorded entries; human; tablet; also "20 mg doxycycline hyclate", "Vibramycin, 100 mg, QD plus metornidazole", "Oracea® 40 mg plus metronidazole"
Show the evidence
human
NCT00066027
20 mg doxycycline hyclate
NCT00495313
Vibramycin, 100 mg, QD plus metornidazole
NCT00495313
Oracea® 40 mg plus metronidazole
NCT00647959
Doxycycline Tablets, 150mg
NCT00648180
Doxycycline Monohydrate Tablets 100 mg
NCT00649571
Doxycycline Monohydrate Tablets (100 mg
14 more recorded rows
humanNCT00775177
Doxycycline monohydrate 100mg tablets
humanNCT00892281
doxycycline (Oracea®) 40 mg modified release as monotherapy
humanNCT00892281
doxycycline (Oracea®) 40 mg modified release as add-on therapy
tablet; Each tablet contains 100 mg of Doxycycline
humanNCT02553083
doxycycline 200 mg
humanNCT03448731
Doxycycline 50Mg Tablet
humanNCT03457636
Doxycycline Anhydrous 40 MG
humanNCT03960411
Doxycycline 100Mg Capsule
recorded 2026-09-01 · last checked 2026-09-04
Q6
Doxycycline Anhydrous's half-life is 18 to 22 hours — which schedules were studied?
18 to 22 hours, the half-life Doxycycline Anhydrous's label states: "Specific Populations Patients with Renal Impairment Studies have shown no significant difference in the serum half-life of doxycycline (range 18 to 22 hours) in individuals with normal and severely impaired renal function." DailyMed label · 3ae4ca12-be39-46b9-bc4c-f8356776c175 · 2026-04-28
tmax 3 hours.
Show the evidence
half lifepharmacokinetics
18 to 22 hours; Specific Populations Patients with Renal Impairment Studies have shown no significant difference in the serum half-life of doxycycline (range 18 to 22 hours) in individuals with normal and severely impaired renal function.
tmaxpharmacokinetics
3 hours; Following single and multiple-dose administration of doxycycline hyclate delayed-release tablets, 200 mg to adult volunteers, average peak plasma doxycycline concentration (C max ) was 4.6 mcg/mL and 6.3 mcg/mL, respectively with median t max of 3 hours; the corresponding mean plasma concentration values 24 hours after single and multiple doses were 1.5 mcg/mL and 2.3 mcg/mL, respectively.
recorded 2026-04-28 · last checked 2026-09-04
Q7
Which running trial of Doxycycline Anhydrous could settle lifespan?
NCT06446245 measures Mortality or severe neurological deficits (modified Rankin scale of 3 or more) at 8 weeks, from time of randomization., reading out 2027-12.
2 open trials; n 200; "Adjunctive Doxycycline for Central Nervous System Tuberculosis"
Show the evidence
Trial
NCT06446245
"Adjunctive Doxycycline for Central Nervous System Tuberculosis"; n 200; "Mortality or severe neurological deficits (modified Rankin scale of 3 or more) at 8 weeks, from time of randomization."; 2027-12
NCT07215325
"Got Doxy- 'Flipping the Script' on STI PEP"; n 200; "Composite inflammation score"; 2029-04-13
Q8
Which 88 trials of Doxycycline Anhydrous posted no result?
Posted no result
88 of 88 completed trials
Registrations
NCT00652704, NCT00653380, NCT01380496, NCT01380483, NCT00001101 and NCT00000403, and 82 more
Completion dates
oldest 1999-09; newest 2024-01-01
Show the evidence
Trial
NCT00652704
1999-09
NCT00653380
1999-10
NCT01380496
1999-11
NCT01380483
2000-04
NCT00001101
2001-03
NCT00000403
2001-07
14 further recorded trials
NCT00652795
2004-09
NCT00126399
2005-04
NCT00649571
2005-07
NCT00538967
2005-08
NCT00648180
2005-08
NCT00775177
2005-08
NCT00775918
2005-08
NCT00066027
2005-10-01
NCT00000938
2005-11
NCT00351182
2005-12
NCT00647959
2006-04
NCT00177333
2006-05
NCT00126204
2006-07
NCT00439400
2007-08
Q9
At the median, Doxycycline Anhydrous's trials enrolled 74 people — anything larger?
Median enrolment
74
Largest enrolment
4618
Registered trials counted
274
Q10
What do 3617 spontaneous reports say about Doxycycline Anhydrous — 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.
Doxycycline Anhydrous appears in spontaneous reports to regulators. Across the 10 most-reported reaction terms, 3617 reaction mentions were counted: drug hypersensitivity 1654; vomiting 577; rash 553; jarisch-herxheimer reaction 208. FAERS via Open Targets · CHEMBL1200699 · 2026-06-24
Show the evidence
drug hypersensitivity
1654
vomiting
577
rash
553
jarisch-herxheimer reaction
208
pancreatitis acute
164
photosensitivity reaction
133
4 more recorded rows
oesophageal ulcer
115
oesophagitis
92
intracranial pressure increased
64
gastrointestinal mucosal necrosis
57
recorded 2026-06-24 · last checked 2026-09-04
Q11
Which 10 reactions does Doxycycline Anhydrous's label not list?
drug hypersensitivity, gastrointestinal mucosal necrosis and intracranial pressure increased and 7 more reported for Doxycycline Anhydrous, absent from its label. FAERS via Open Targets · CHEMBL1200699 · 2026-06-24
2 label terms; 10 reported and unlisted; 3ae4ca12-be39-46b9-bc4c-f8356776c175
Show the evidence
drug hypersensitivity
count not stated
gastrointestinal mucosal necrosis
count not stated
intracranial pressure increased
count not stated
jarisch-herxheimer reaction
count not stated
oesophageal ulcer
count not stated
oesophagitis
count not stated
4 more recorded rows
pancreatitis acute
count not stated
photosensitivity reaction
count not stated
rash
count not stated
vomiting
count not stated
recorded 2026-06-24 · last checked 2026-09-04
Where it is registeredIdentifiers, relations and other names
ChEMBL 37 — CC BY-SA 3.0 Unported · ChEMBL ATC CC BY-SA · ClinicalTrials.gov — US Government work · Open Targets 26.06 — CC0 · mixed register set; per-register licences in docs/specs/corpus-20k-sources.md · openFDA / DailyMed — US Government work
✗ required summary fields resolved: 4 required field(s) not terminal: Why people use it, Best-supported result, Biggest unanswered question, Human evidence
✓ public claims reviewed: 0 reviewed claim(s); drafts are never rendered
✓ source coverage passed: 6 source rows
✓ no critical contamination: no quarantine open
✓ canonical metadata passed: slug and display name present
✓ no raw internal fields: enforced by the copy-contract test over the rendered page
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.