This page shows what was measured, who it was measured in, and what that does not settle.
What Famotidine does in the body
Heartburn and acid indigestion, and healing of stomach and duodenal ulcers
The cells that make stomach acid are switched on by three separate chemical messages, and histamine is by far the strongest of them. Famotidine sits on the histamine receptor on the outside of those cells and blocks it, so the loudest signal never gets through and the cell turns its acid production down. Because it blocks a switch rather than destroying the machinery, it works within about an hour and wears off as the drug leaves the body. It also means the cell can partly get around the block over a few days, which is why the effect fades with regular use in a way a proton pump inhibitor’s does not.
What happened in people
Time to COVID-19 symptom resolution not improved against placebo in 55 randomised outpatients (P=0.4)
✎ 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.
Became effectively the only H2 blocker on the American market after ranitidine was withdrawn worldwide in April 2020
Where it acts
Basolateral membrane of the gastric parietal cell — the outside face of the cell, not the acid-secreting channel inside it
Kind of result
Symptoms and quality of life
Supervision
RNAWiki has not recorded a supervision or regulatory status for this substance.
What the registries record it as
The substance registry classes this as chemical.
FDA substance registry · 5QZO15J2Z8 · read 2026-08-29
Where each sentence above came from
No recorded sentence describes the change this makes in a way that stands on its own. The page opens with what it is taken for instead, and the recorded explanation follows below.
Shown as the opening line on this page.
A limit recorded against this substance. Not signed off as a reviewed claim.
The four opening statements run to 140 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.
Proportion healed and proportion heartburn-free at up to 12 weeks, by drug class
✓ The study showed what it set out to show
Who was studied
Chiba pooled analysis of 43 randomised oesophagitis trials
How many people
7635
Study design
Meta-analysis of single- and double-blind randomised trials
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
H2-receptor antagonists 51.9% (SD 17.1) against proton pump inhibitors 83.6% (11.4), sucralfate 39.2% (22.4) and placebo 28.2% (15.6); healing speed 5.9% per week against 11.7% and 2.9%
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. A class-level pooled estimate, not a head-to-head trial of famotidine specifically, and the endpoint is endoscopic appearance rather than any patient outcome.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet, orally disintegrating tablet, oral suspension, chewable over-the-counter tablet, and intravenous solution including a preservative-free presentation
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
Cluster crossover randomised clinical trial, 50 ICUs in 5 countries
Compared against
Not recorded for this study
Kind of result
Living longer, or avoiding a major event
What was found
18.3% on the proton pump inhibitor strategy against 17.5% on the H2 blocker strategy; risk ratio 1.05 (95% CI 1.00 to 1.10), P=0.054
Repeated elsewhere
Unreplicated
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. An estimated 20.1% of patients randomised by site to H2 blockers actually received a proton pump inhibitor. That crossover biases the comparison toward the null and the authors say so.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet, orally disintegrating tablet, oral suspension, chewable over-the-counter tablet, and intravenous solution including a preservative-free presentation
Interval reported. 95% CI 1
Written into the record, not signed off as a reviewed claim.
Not statistically improved, P=0.4. Secondary rate of symptom resolution improved, P<0.0001, with 50% reduction of baseline symptom score at 8.2 days (95% CI 7 to 9.8) against 11.4 days (10.3 to 12.6).
Repeated elsewhere
Unreplicated
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. Fifty-five participants, median age 35, all unvaccinated outpatients. The trial was not designed or powered to detect an effect on hospitalisation or death, and the authors state further randomised trials are required.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet, orally disintegrating tablet, oral suspension, chewable over-the-counter tablet, and intravenous solution including a preservative-free presentation
Interval reported. 95% CI 7 to 9
Written into the record, not signed off as a reviewed claim.
Twenty-four-hour urinary excretion of N-nitrosodimethylamine
✗ The study did not show it
Who was studied
Ranitidine and urinary NDMA excretion (NCT04397445)
How many people
18
Study design
Randomised, double-blind, placebo-controlled crossover in healthy volunteers
Compared against
A dummy treatment
Kind of result
A number that stands in for health
What was found
No significant difference on a non-cured-meats diet (median paired difference 0 ng, IQR -6.9 to 0, P=0.54) or a cured-meats diet (-1.1 ng, IQR -9.1 to 11.5, P=0.71)
Repeated elsewhere
Unreplicated
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. The trial is about ranitidine, not famotidine, and appears here because it is the reason famotidine has the H2 blocker market to itself. The withdrawal rests on contamination found in the product, which this trial does not address.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet, orally disintegrating tablet, oral suspension, chewable over-the-counter tablet, and intravenous solution including a preservative-free presentation
Interval reported. Not recorded in this summary
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.
Where a source records it acting
Stomach: Competitive inhibitor of histamine-2 (H2) receptors; the primary clinically important pharmacologic activity is inhibition of gastric secretion
US prescribing information · 002875d2-8c30-2d2e-e063-6294a90ae01e · read 2026-08-27
Start
Famotidine
What a person takes: Oral tablet, orally disintegrating tablet, oral suspension, chewable over-the-counter tablet, and intravenous solution including a preservative-free presentation.
The measurement behind this step
No enteric coating is needed, because unlike the proton pump inhibitors this molecule is stable in gastric acid. Onset is within about an hour by mouth, which is the property that keeps it in use alongside more effective drugs. The intravenous form is widely used in hospital, including as stress ulcer prophylaxis.
Getting in
Swallowed plain, with no coating needed
Unlike the proton pump inhibitors, this molecule is perfectly stable in stomach acid, so the tablet needs no protective shell. It starts being absorbed straight away.
──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
Famotidine is acid-stable and orally bioavailable at 40 to 45%, unaffected by food. Peak plasma concentration comes at one to three hours and the plasma half-life is 2.5 to 3.5 hours — which, unlike a proton pump inhibitor, is close to the duration of its effect, because the effect ends when the drug leaves the receptor.
It works on the outer surface of the stomach cell, not inside the acid channel. Nothing has to trap it and nothing has to activate it.
╌╌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
The H2 receptor sits on the basolateral membrane, facing the bloodstream rather than the gastric lumen. Famotidine is highly polar, with a logP near -0.2, and does not need to cross a membrane or accumulate in an acidic compartment to reach its target.
Three chemicals tell the stomach cell to make acid, and histamine is the loudest. Famotidine sits in the histamine slot so that message never arrives. The other two signals also weaken, because much of their effect works through histamine.
╌╌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
Competitive, surmountable, fully reversible antagonism at the Gs-coupled H2 receptor. Blocking it prevents adenylyl cyclase activation and the rise in cyclic AMP that drives protein kinase A. Because gastrin and acetylcholine act substantially through histamine release from enterochromaffin-like cells, blocking H2 attenuates all three stimulatory arms rather than one.
The pump is never activated, but never destroyed either
The acid pump itself is untouched. It simply never receives the instruction to move to the cell surface and start working. That is why the effect is complete only while the drug is present.
╌╌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
Without protein kinase A signalling, the H+/K+-ATPase-containing tubulovesicles do not fuse with the canalicular membrane and the pump is not inserted into the secretory surface. No covalent chemistry occurs anywhere. Acid secretion resumes as receptor occupancy falls.
Over a few days of regular dosing, the same dose suppresses less acid. Blocking a receptor is the kind of intervention a cell can compensate for; destroying the pump is not.
──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
Tolerance to the antisecretory effect is established in healthy volunteers with repeated oral dosing and reported with intravenous dosing. Receptor upregulation is the usual proposed mechanism and is not proven in humans. The reviews note it is less pronounced in duodenal ulcer patients than in volunteers, and its clinical significance remains contested.
The liver barely processes it, which is why it interacts with almost nothing. The kidney does the work instead, so when kidney function falls the drug builds up — and in older people that shows up as confusion.
──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
Roughly 65 to 70% is excreted unchanged, most of it renally, with minimal cytochrome P450 involvement — the reason famotidine has none of the interaction profile that made cimetidine notorious. In renal impairment, accumulation produces the central nervous system adverse effects recorded in the label: confusion, delirium, hallucinations, agitation, most often in elderly patients.
No suggested links are held for this record, so nothing is hidden from this path.
What we know
The record describes 6 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.
Adults and children with reflux or ulcer disease, an enormous number of people self-treating heartburn off a supermarket shelf, and — during the COVID-19 pandemic — a great many people taking it on the strength of a hypothesis that had not been tested.
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: “Peptic Ulcer Disease and GERD With or Without Esophagitis and Ulcerations Pediatric Patients One Year to Less than 17 Years of Age: The safety and effectiveness of famotidine for oral suspension have been established in pediatric patients 1 year to less than 17 years of age for the treatment of peptic ulcer disease and GERD with or without esophagitis and ulcerations.”
US prescribing information · 900b4fd6-9c62-4b64-b4db-760c49ae0a42 · read 2026-08-30
On older people, the label states: “Of the 1442 famotidine-treated patients in clinical studies, approximately 10% were 65 and older.”
US prescribing information · 900b4fd6-9c62-4b64-b4db-760c49ae0a42 · read 2026-08-30
On people who are pregnant, the label states: “Risk Summary Available data with H 2 -receptor antagonists, including famotidine, in pregnant women are insufficient to establish a drug-associated risk of major birth defects, miscarriage or adverse maternal or fetal outcomes.”
US prescribing information · 900b4fd6-9c62-4b64-b4db-760c49ae0a42 · read 2026-08-30
On people who are breastfeeding, the label states: “Risk Summary There are limited data available on the presence of famotidine in human breast milk.”
US prescribing information · 900b4fd6-9c62-4b64-b4db-760c49ae0a42 · read 2026-08-30
On people with reduced kidney function, the label states: “CNS adverse reactions and prolonged QT intervals have been reported in patients with moderate and severe renal impairment [see WARNINGS AND PRECAUTIONS (5.1) ].”
US prescribing information · 900b4fd6-9c62-4b64-b4db-760c49ae0a42 · read 2026-08-30
Where the result stopped carrying
Tolerance: the antisecretory effect shrinks within days of repeated dosing, a limitation the mechanism makes unavoidable
The COVID-19 primary endpoint was not met, though the drug was safe and a secondary rate measure favoured it
Renal accumulation causes confusion and delirium in older patients, a harm found through use rather than through a trial
PEPTIC could not deliver a clean comparison, because a fifth of the H2 blocker arm received a proton pump inhibitor instead
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.
Other reasons RNAWiki checked and found nothing for (11)
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.
The product may not be what it says
Contents of a sold product are not always what the label states. Nothing in this record points to this reason.
No recorded reason
RNAWiki has nothing stored that would explain it. Nothing in this record points to this reason.
None of these is a reason to take more. Taking more is not a step this page ever suggests.
What it would be like to take◇Read from sources, not yet reviewed
What taking it involves
The recorded facts about getting hold of it and using it. Nothing here is a suggestion about what you should do.
How it is supplied
Given by a clinician
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
Read from the recorded approval status.
No source is stored against this line.
Form and route
Oral tablet, orally disintegrating tablet, oral suspension, chewable over-the-counter tablet, and intravenous solution including a preservative-free presentation
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form and route recorded on this substance.
No source is stored against this line.
Who oversees it
RNAWiki has not recorded a supervision or regulatory status for this substance.
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
No register row and no identity class settled the question.
No source is stored against this line.
What is in the pack
No enteric coating is needed, because unlike the proton pump inhibitors this molecule is stable in gastric acid. Onset is within about an hour by mouth, which is the property that keeps it in use alongside more effective drugs. The intravenous form is widely used in hospital, including as stress ulcer prophylaxis.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on how this is sold and what that means for what is in the pack.
No source is stored against this line.
Where it is registered
Regulatory records are listed in the technical disclosure at the foot of this page.
# Counted from records
Where this came from
A count of rows RNAWiki holds. It describes our records, not your body.
Register entries are stored per jurisdiction and shown with their dates.
No source is stored against this line.
Why people stop
Not recorded.
∅ Nothing recorded
Where this came from
RNAWiki holds nothing here and says so rather than guessing.
No record of why people stopped taking it is stored for this substance.
No source is stored against this line.
What it would be like to take◇Read from sources, not yet reviewed
What can go wrong
Sorted by where each line came from. A regulator's label and a report somebody sent in are not the same kind of fact.
·Worth asking a clinician aboutWritten into the record from the studies named on this page
The label records central nervous system adverse effects — confusion, delirium, hallucinations, disorientation, agitation, seizure — in patients with moderate or severe renal impairment, in whom the drug accumulates because it is cleared largely unchanged by the kidney. QT prolongation has been reported in the same setting. Commonest adverse reactions are headache, dizziness, constipation and diarrhoea. Cytochrome P450 involvement is minimal, so the drug interaction profile is unusually clean; the interactions that do matter are with drugs whose absorption depends on gastric acidity.
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 tablet, orally disintegrating tablet, oral suspension, chewable over-the-counter tablet, and intravenous solution including a preservative-free presentation
✎ 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
Onset is within about an hour by mouth, which is the property that keeps it in use alongside more effective drugs. The intravenous form is widely used in hospital, including as stress ulcer prophylaxis.
✎ 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
466 products list this as an active ingredient in the United States drug directory. 390 of them contain it and nothing else.
FDA National Drug Code directory · 72162-2599 · read 2026-08-29
They are sold as for suspension, granule, injection, injection, solution, powder and powder, for solution, taken intravenous and oral.
FDA National Drug Code directory · 72162-2599 · read 2026-08-29
The regulator's established pharmacologic class for it is histamine h2 receptor antagonists [moa] and histamine-2 receptor antagonist [epc].
FDA National Drug Code directory · 72162-2599 · read 2026-08-29
373 published labels name it as an active ingredient. 302 of them describe this substance alone, which is where its own label text on this page comes from.
US prescribing information · 900b4fd6-9c62-4b64-b4db-760c49ae0a42 · read 2026-08-29
Those labels are classed as human otc drug and human prescription drug.
US prescribing information · 900b4fd6-9c62-4b64-b4db-760c49ae0a42 · read 2026-08-29
Famotidine is film-coated tablets at Tablets: 20 mg, 40 mg, recorded as prescription product; fda label in effect 2025-10-22 in the United States.
US prescribing information · 002875d2-8c30-2d2e-e063-6294a90ae01e · read 2026-08-27
Recorded price in US: 0.02862–0.14252 USD per one unit as the pricing file counts it — a tablet, capsule, patch or single item, across 91 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: 0.07766–0.4942 USD per one millilitre, across 21 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.
RNAWiki could not confidently classify this substance, so no self-experiment plan is offered.
Questions worth asking
Which of the trials of Famotidine 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 famotidine treats COVID-19 — an observational association whose randomised test missed its primary endpoint in 55 people
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 ranitidine converts to a carcinogen inside the body, the hypothesis behind the citizen petition, refuted by a randomised crossover trial
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 long safe use is equivalent to a systematic safety trial; no COMPASS-scale placebo-controlled study exists for this class
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 H2 blocker is interchangeable with a proton pump inhibitor for healing erosive disease, when the pooled difference is 32 percentage points
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
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 Famotidine 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.
Half the healing of a proton pump inhibitor, at half the speed
In plain words
Pooling 43 randomised trials in 7,635 people, H2 blockers healed erosive damage to the oesophagus in about half of patients and proton pump inhibitors in about five in six. Placebo healed a quarter. The healing also happened about twice as fast on the stronger drug.
What was measured
Proportion healed and heartburn-free at up to 12 weeks, pooled across 43 randomised trials in 7,635 patients, by drug class
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Chiba and colleagues applied strict inclusion criteria to single- or double-blind randomised studies in adults with endoscopically proven erosive or ulcerative oesophagitis. Mean healing proportion within 12 weeks was 51.9% (SD 17.1) for H2-receptor antagonists against 83.6% (11.4) for proton pump inhibitors, 39.2% (22.4) for sucralfate and 28.2% (15.6) for placebo. Healing speed was 5.9% per week against 11.7% for PPIs and 2.9% for placebo. Corrected heartburn-free proportions were 47.6% (15.5) against 77.4% (10.4). The endpoint throughout is mucosa seen down an endoscope.
Written into the record, not signed off as a reviewed claim
It stops working as well within days, and this is established, not disputed
In plain words
The acid-suppressing effect of this drug class shrinks with repeated dosing over a few days. That has been demonstrated in healthy volunteers and it is a property of the mechanism — blocking a receptor prompts the cell to make more receptors.
What was measured
Attenuation of the antisecretory effect on repeated dosing, measured by intragastric pH in healthy volunteers
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
Diminution of the antisecretory effect with repeated oral dosing, termed tolerance, is established in healthy volunteers across the H2-receptor antagonist class, with anecdotal evidence of the same phenomenon on intravenous dosing. The review that summarises the literature is explicit that tolerance may be clinically relevant where tight control of acidity is required. It is equally explicit about the limits of the evidence: patients with duodenal ulcer disease do not appear to develop significant tolerance according to the sparse investigations available, and the mechanisms remain unclear. Receptor upregulation is the usual explanation and has not been proved to be the operative one in humans. The important asymmetry is that a proton pump inhibitor cannot show this behaviour, because it destroys the pump rather than occupying a receptor.
Written into the record, not signed off as a reviewed claim
The COVID-19 trial missed its primary endpoint, and the observational study that started it all was retrospective
In plain words
Early in the pandemic a hospital database study suggested famotidine users did better, and a great deal of public attention followed. When a randomised trial was finally run, in 55 outpatients, the primary endpoint — how quickly symptoms went away — was not met. A secondary measure of the rate of resolution did favour the drug.
What was measured
Time to symptom resolution in 55 randomised non-hospitalised adults with COVID-19, against matching placebo
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
The originating signal was a propensity-score-matched retrospective cohort of hospitalised COVID-19 patients reporting an association between famotidine use and improved outcomes. The randomised test was a double-blind, placebo-controlled, fully remote phase 2 trial enrolling 55 symptomatic unvaccinated adult outpatients with confirmed COVID-19 at two United States centres between January and April 2021, self-administering 80 mg famotidine or placebo three times daily for 14 days. Median age was 35. The primary endpoint, time to symptom resolution, was not statistically improved (P=0.4). The secondary endpoint, rate of symptom resolution, was improved (P<0.0001), with estimated 50% reduction of baseline symptom scores at 8.2 days (95% CI 7 to 9.8) against 11.4 days (10.3 to 12.6). Fewer patients on famotidine had detectable plasma interferon alpha at day 7 (P=0.04). The authors state that additional randomised trials are required. Fifty-five participants is a phase 2 sample and the trial was not designed to detect an effect on hospitalisation or death.
Written into the record, not signed off as a reviewed claim
Famotidine inherited the market because ranitidine was withdrawn — and the mechanism everyone assumed turned out to be wrong
In plain words
In 2020 every ranitidine product was pulled worldwide because it contained a probable carcinogen. The petition that triggered it argued the drug turned into that carcinogen inside the body. A randomised trial then tested exactly that and found no increase at all. The contamination was in the product, not in the patient.
What was measured
That ranitidine is converted to a carcinogen inside the body — the hypothesis behind the citizen petition, tested in a randomised crossover trial and not supported
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The FDA requested withdrawal of all ranitidine products in April 2020 after N-nitrosodimethylamine was detected and shown to increase in the product with time and with storage temperature. The 2019 citizen petition had proposed a second and more alarming mechanism: that ranitidine converts to NDMA within the human body, based largely on a small clinical study of urinary NDMA. A randomised, double-blind, placebo-controlled crossover trial in 18 healthy participants then measured 24-hour urinary NDMA excretion after 300 mg oral ranitidine against placebo, on both a non-cured-meats and a cured-meats diet. There was no statistically significant difference on either diet — median paired differences of 0 ng (IQR -6.9 to 0, P=0.54) and -1.1 ng (IQR -9.1 to 11.5, P=0.71). The cured-meats diet raised NDMA excretion far more than the drug did. The withdrawal stands on product contamination, which is a real and sufficient reason. The in-body conversion hypothesis, which drove much of the alarm, was tested and not supported.
Written into the record, not signed off as a reviewed claim
In 26,828 ventilated patients, H2 blockers were numerically better on mortality than proton pump inhibitors
In plain words
The largest comparison ever run between the two ways of preventing stress ulcers in intensive care found the stronger drug bled slightly fewer patients and the weaker drug had slightly fewer deaths. Neither difference in mortality reached the significance threshold.
What was measured
All-cause in-hospital mortality within 90 days, and clinically important upper gastrointestinal bleeding, PPI strategy against H2 blocker strategy
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
PEPTIC was a cluster crossover randomised trial at 50 intensive care units in five countries, in which each unit used a preferential proton pump inhibitor strategy and a preferential H2 blocker strategy for six months each in random order. Of 26,982 randomised, 26,828 were analysed. In-hospital mortality by day 90 was 2,459 of 13,415 (18.3%) in the PPI group against 2,333 of 13,356 (17.5%) in the H2 blocker group — risk ratio 1.05 (95% CI 1.00 to 1.10), absolute difference 0.93 percentage points (95% CI -0.01 to 1.88), P=0.054. Clinically important upper gastrointestinal bleeding was 1.3% against 1.8%, risk ratio 0.73 (95% CI 0.57 to 0.92), P=0.009, favouring the proton pump inhibitor. C. difficile rates and lengths of stay did not differ. Interpretation is limited by crossover: an estimated 20.1% of patients randomised by site to H2 blockers actually received a proton pump inhibitor, which would bias the mortality comparison toward the null.
Written into the record, not signed off as a reviewed claim
Its safety reputation rests on the absence of evidence rather than on trials
In plain words
Famotidine is generally described as very safe, and it probably is. What it does not have is what pantoprazole has: a placebo-controlled trial in tens of thousands of people over years, systematically counting harms. Its record is built from decades of use rather than from a trial designed to find problems.
What was measured
That long familiarity with a drug is equivalent to a systematic safety trial — a common inference, and the reason the proton pump inhibitor safety questions were answerable in 2019 while the H2 blocker ones are not
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
No placebo-controlled randomised trial of famotidine comparable in scale or duration to the COMPASS proton pump inhibitor substudy — 17,598 participants, median 3.01 years, fourteen prespecified safety outcomes collected six-monthly — has been conducted for this molecule or for its class. What exists is a very large post-marketing experience, the label’s recorded adverse reactions, and a known and mechanistically explicable problem: the drug is cleared largely unchanged by the kidney, so in renal impairment it accumulates and produces central nervous system effects including confusion, delirium and agitation, most often in older patients. That is a well-characterised harm found through use rather than through a trial. Describing the drug as proven safe overstates what the record contains; describing it as unsafe would overstate it in the other direction.
Source
PEPCID United States prescribing information, Warnings and Precautions and Adverse Reactions (NDA 019462); Moayyedi P et al., Gastroenterology 2019;157:682-691 for the comparison
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
caution
Review state
Written into the record, not signed off as a reviewed claim
How many documents were read
292 documents were read for this substance.
RNAWiki source record
Where else this substance is registered
FDA substance identifier (UNII)
5QZO15J2Z8
CAS registry number
76824-35-6
PubChem compound
5702160
RxNorm concept
4278
Checks this page had to pass
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no quarantine open
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Every public sentence names a source
The opening statement carries the origin: Written into the record, not signed off.
✗ Not passed
Trial roles classified for highlighted evidence
No registered study is classified as testing this substance.
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No internal keys in reader text
enforced by the copy-contract test over the rendered page
✗ Not passed
Safety mode resolved
No register row and no identity class settled the question.
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Canonical metadata present
slug and display name present
What is missing or unclear◇Read from sources, not yet reviewed
How this medicine reached us
Kept near the foot of the page. A historical event moves up only when it changes something about this substance today.
Withdrawn in United States, 2025, for "Microbial Contamination of Sterile Products; out of limit results obtained for endotoxin testing." (openFDA drug enforcement Class I recall)
What the approval register records
114 approved applications cover products containing this substance. The earliest was NDA019462, approved 19861015 to BAUSCH.
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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 histamine H2-receptor blocker that turns down the loudest of the three signals telling the stomach to make acid, without touching the pump itself: it heals erosive oesophagitis in 51.9% of patients pooled across 43 trials against 83.6% for a proton pump inhibitor and 28.2% for placebo, loses part of its effect within days of continuous dosing, and — in the only randomised trial of it against placebo in COVID-19 — missed its primary endpoint of time to symptom resolution at P=0.4 in 55 outpatients.
Recorded evidence blocks (10)
Q1
On the Famotidine label: indicated for what?
"Famotidine tablets are indicated in adult and pediatric patients 40 kg and greater for the treatment of: • active duodenal ulcer (DU). • active gastric ulcer (GU).": indications and usage on Famotidine's label. DailyMed label · 599642c8-51cd-4220-e063-6394a90a5e20 · 2026-08-24
Q2
102 registered trials of Famotidine — at which phases?
16 of Famotidine's trials stopped: safety, futility/efficacy, accrual/recruitment, funding/business, other?
safety (1), futility/efficacy (1), accrual/recruitment (8), funding/business (3) and other (3): Famotidine's stop wording, clustered. CLINICALTRIALS_SNAPSHOT · 2026-09-01
"low enrollment"; 16 of 102 registered studies
Show the evidence
Trial
NCT04248712
terminated; "low enrollment"
NCT04545008
terminated; "Study was stopped due to poor accrual."
NCT04565392
withdrawn; "lack of funding"
NCT04614974
terminated; "Slow recruitment due to few eligible patients"
NCT04621149
terminated; "Unable to recruit participants due to decline in COVID-19."
NCT04766996
terminated; "Loss of surgery team member deemed the study procedures impossible to achieve, and no replacement could be found in a timely manner to complete trial as initially planned."
10 further recorded trials
NCT04836806
withdrawn; "Study stopped due to issues with enrollment and lack of funding."
NCT04840615
terminated; "Study was closed early due to slow accrual."
NCT04918147
terminated; "The study was terminated early based on disease flare/lack of efficacy in the early phase of the trial."
NCT04990388
terminated; "Sponsor decision not related to safety concerns"
NCT05035407
terminated; "Site plans to become a site for a multicenter study of this therapy"
NCT05077969
terminated; "Low recruitment"
NCT05085574
withdrawn; "COVID environment, lack of site confidence to enroll subjects, sites not suited to study procedures, decline of potential inpatient subjects at site"
NCT05946551
terminated; "Study was terminated due to lack of funding."
NCT05965492
withdrawn; "Study drug was not compliant with research pharmacy"
NCT06144697
terminated; "Business objectives have changed"
recorded 2026-09-01 · last checked 2026-09-04
Q4
Human studies of Famotidine used famotidine 20 mg — over how long?
Human studies of Famotidine used "famotidine 20 mg". ClinicalTrials.gov · 2026-09-01
8 recorded entries; human; also "Famotidine Tablets, 40 mg", "famotidine 40 mg", "Famotidine 40 mg"
Show the evidence
human
NCT00633035
famotidine 20 mg
NCT00802828
Famotidine Tablets, 40 mg
NCT02551744
famotidine 40 mg
NCT02684799
Famotidine 40 mg
NCT03554291
Famotidine 20 MG
NCT05084521
Famotidine 400 mg/50 mL
2 more recorded rows
humanNCT06332638
Famotidine 20mg
humanNCT06332638
Gaster Tab. 20 mg Dong-A
recorded 2026-09-01 · last checked 2026-09-04
Q5
Famotidine's half-life is 2.5 to 3.5 hours — which schedules were studied?
NCT01511731, NCT01928888, NCT00229424, NCT01079052, NCT01079065 and NCT00843063, and 43 more
Completion dates
oldest 1998-10; newest 2024-05-25
Show the evidence
Trial
NCT01511731
1998-10
NCT01928888
2004-02
NCT00229424
2007-01
NCT01079052
2007-12
NCT01079065
2007-12
NCT00843063
2008-12
14 further recorded trials
NCT00633035
2010-04
NCT00451880
2011-10
NCT00565175
2011-12
NCT02555852
2012-02
NCT01937078
2014-03
NCT02097329
2014-06
NCT02410460
2014-06
NCT02684799
2016-04-11
NCT01408186
2016-11
NCT02534636
2016-11
NCT02763969
2016-12-15
NCT02922933
2017-05-08
NCT03302845
2017-11-07
NCT03142165
2017-11-29
Q7
At the median, Famotidine's trials enrolled 37.5 people — anything larger?
Median enrolment
37.5
Largest enrolment
4238504
Registered trials counted
102
Q8
What do 795 spontaneous reports say about Famotidine — 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.
Famotidine appears in spontaneous reports to regulators. Across the 10 most-reported reaction terms, 795 reaction mentions were counted: liver disorder 143; hepatic function abnormal 100; rhabdomyolysis 91; alanine aminotransferase increased 86. FAERS via Open Targets · CHEMBL902 · 2026-06-24
Show the evidence
liver disorder
143
hepatic function abnormal
100
rhabdomyolysis
91
alanine aminotransferase increased
86
aspartate aminotransferase increased
81
platelet count decreased
79
4 more recorded rows
electrocardiogram qt prolonged
62
delirium
58
blood creatine phosphokinase increased
49
agranulocytosis
46
recorded 2026-06-24 · last checked 2026-09-04
Q9
Which 10 reactions does Famotidine's label not list?
agranulocytosis, alanine aminotransferase increased and aspartate aminotransferase increased and 7 more reported for Famotidine, absent from its label. FAERS via Open Targets · CHEMBL902 · 2026-06-24
2 label terms; 10 reported and unlisted; 599642c8-51cd-4220-e063-6394a90a5e20
Show the evidence
agranulocytosis
count not stated
alanine aminotransferase increased
count not stated
aspartate aminotransferase increased
count not stated
blood creatine phosphokinase increased
count not stated
delirium
count not stated
electrocardiogram qt prolonged
count not stated
4 more recorded rows
hepatic function abnormal
count not stated
liver disorder
count not stated
platelet count decreased
count not stated
rhabdomyolysis
count not stated
recorded 2026-06-24 · last checked 2026-09-04
Q10
Famotidine and CYP1A2, OAT1 and OAT3: shared by which compounds?
( 7.1 ) • Tizanidine (CYP1A2) Substrate: Potential for substantial increases in blood concentrations of tizanidine resulting in hypotension, bradycardia or excessive drowsiness; avoid concomitant use, if possible.
drug_interactions
7.2 Tizanidine (CYP1A2 Substrate) Although not studied clinically, famotidine is considered a weak CYP1A2 inhibitor and may lead to substantial increases in blood concentrations of tizanidine, a CYP1A2 substrate.
pharmacokinetics
Drug Interaction Studies Human Organic Anion Transporter (OAT) 1 and 3: In vitro studies indicate that famotidine is a substrate for OAT1 and OAT3.
pharmacokinetics
Following coadministration of probenecid (1500 mg), an inhibitor of OAT1 and OAT3, with a single oral 20 mg dose of famotidine in 8 healthy subjects, the serum AUC 0 to 10h of famotidine increased from 424 to 768 ng•hr/mL and the maximum serum concentration (C max ) increased from 73 to 113 ng/mL.
pharmacokinetics
Multidrug and Toxin Extrusion Protein 1 (MATE-1): An in vitro study showed that famotidine is an inhibitor of MATE-1.
pharmacokinetics
However, no clinically significant interaction with metformin, a substrate for MATE-1, was observed.
2 more recorded rows
Interaction statementpharmacokinetics
CYP1A2: Famotidine is a weak CYP1A2 inhibitor.
Interaction statementclinical_pharmacology
Drug Interaction Studies Human Organic Anion Transporter (OAT) 1 and 3: In vitro studies indicate that famotidine is a substrate for OAT1 and OAT3.
Withdrawn in United States, 2025, for "Microbial Contamination of Sterile Products; out of limit results obtained for endotoxin testing." (openFDA drug enforcement Class I recall)
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 · openFDA enforcement — 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: 7 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
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