Over-the-counter medication · H2 Receptor Antagonist
cimetidine
Also sold as Tagamet. Cimetidine treats active duodenal ulcers for short periods.
Data updated 2026-05-15
- 9,140
- FDA reportsLightly reported
- 77
- InteractionsMany interactions
- $0.26
- Generic price (NADAC)
What the data shows
cimetidine (Tagamet) is an over-the-counter H2 Receptor Antagonist, reported less often than most tracked drugs (9,140 FDA reports), with 77 documented drug interactions.
Reporting volume reflects how widely a drug is used and studied, not how dangerous it is, a FAERS report documents a temporal association, never proof of cause.
cimetidine (Tagamet) is an over-the-counter H2 Receptor Antagonist. Cimetidine treats active duodenal ulcers for short periods.
Cimetidine (Tagamet) reduces stomach acid. It is used to treat ulcers, heartburn, and other conditions where too much acid is produced.
Verify with FDA → · CMS NADAC pricing →
Drug Pricing (NADAC)
Generic Price
$0.26/unit
Generic Available
Yes (9 manufacturers)
Pricing data from NADAC (CMS), effective December 18, 2024. Compare all drug costs →
What it does
Cimetidine treats active duodenal ulcers for short periods.
Common side effects
Headache, Dizziness, Diarrhea
Key warnings
Reversible confusional states (like mental confusion, agitation, or hallucinations) have been reported, mostly in severely ill patients.
The sections below are summarized in plain English from cimetidine's FDA-approved prescribing information. They describe what the official label says, and are not personal medical advice.
How It Works
Cimetidine is an H2 receptor antagonist. This means it blocks histamine from attaching to certain cells in your stomach. By blocking histamine, cimetidine reduces the amount of acid your stomach makes.
Side Effects (from patient reports)
Based on 9,140 FDA adverse event reports.
Most-reported reactions
Adverse reactions in FAERS for cimetidine, by number of reports
- Chronic Kidney Disease
Chronic Kidney Disease
1,264 reports
- Acute Kidney Injury
Acute Kidney Injury
710 reports
- Renal Failure
Renal Failure
694 reports
- Nausea
Nausea
681 reports
- Fatigue
Fatigue
598 reports
- Dyspnoea 504
Dyspnoea
504 reports
- Vomiting 483
Vomiting
483 reports
- Diarrhoea 440
Diarrhoea
440 reports
- Pain 432
Pain
432 reports
- Death 399
Death
399 reports
What this shows Bars show how often each reaction was reported, not how likely it is to happen, a report records a temporal association, never proof that the drug caused it.
Reports over time
Adverse-event reports filed for cimetidine each year to the FDA Adverse Event Reporting System (FAERS).
Year-to-year volume tracks usage, prescribing, and scrutiny, not a change in per-patient risk. Source: FDA FAERS.
Where cimetidine sits
cimetidine has more FDA adverse-event reports than 37% of the drugs FAERS tracks. A high position reflects how widely a drug is used and watched, not how dangerous it is.
Percentile across all drugs PlainMeds tracks by FAERS report volume. The dot is cimetidine; the line is the median (50th percentile).
FDA Adverse Event Report Analysis
Detailed analysis of 9,140 reports from the FDA Adverse Event Reporting System (FAERS). Reports span 1998–2025.
Total Reports
9,140
Reports Mentioning Death
1,168
12.8% of reports — not proof of cause
Hospitalization Reports
3,377
Top Indication
Product Used For Unknown Indication
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 1 | CHRONIC KIDNEY DISEASE | 1,264 |
| 2 | ACUTE KIDNEY INJURY | 710 |
| 3 | RENAL FAILURE | 694 |
| 4 | NAUSEA | 681 |
| 5 | FATIGUE | 598 |
| 7 | DYSPNOEA | 504 |
| 8 | VOMITING | 483 |
| 9 | DIARRHOEA | 440 |
| 10 | PAIN | 432 |
| 11 | DEATH | 399 |
| 12 | DIZZINESS | 386 |
| 14 | HEADACHE | 371 |
| 15 | GASTROOESOPHAGEAL REFLUX DISEASE | 370 |
| 16 | ANXIETY | 348 |
| 17 | END STAGE RENAL DISEASE | 347 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: FDA FAERS (Adverse Event Reporting System) Reports are voluntary and do not establish causation
Serious Warnings
Reversible confusional states (like mental confusion, agitation, or hallucinations) have been reported, mostly in severely ill patients. These usually appear within 2-3 days of starting treatment and clear up within 3-4 days of stopping the drug.
Known Drug Interactions
7.8 Probenecid and Cimetidine No significant effect of probenecid or cimetidine on the Cmax of levofloxacin was observed in a clinical study involving healthy volunteers. The AUC and t 1/2 of levofloxacin were higher while CL/F and CLR were lower during concomitant treatment of levofloxacin with probenecid or cimetidine compared to levofloxacin alone. However, these changes do not warrant dosage adjustment for levofloxacin when probenecid or cimetidine is co-administered.
Mechanism: Cimetidine makes it harder for the kidneys to clear levofloxacin, causing the antibiotic to stay in the body slightly longer.
Interaction Drug Interaction Rifabutin, phenytoin, efavirenz, cimetidine, esomeprazole* Avoid coadministration unless the benefit outweighs the risks ( 7.6 , 7.7 , 7.8 , 7.9 ) Other drugs metabolized by CYP3A4 Consider dosage adjustment and monitor for adverse effects and toxicity ( 7.1 , 7.10 , 7.11 ) Digoxin Monitor digoxin plasma concentrations ( 7.12 ) Fosamprenavir, metoclopramide* Monitor for breakthrough fungal infections ( 7.6 , 7.13 ) *The drug interactions with esomeprazole and metoclopramide do not apply to posaconazole tablets.
Mechanism: Cimetidine changes the environment in the stomach, which can prevent the body from absorbing enough posaconazole into the bloodstream.
Dose adjustment is not recommended for risperidone tablets when co-administered with ranitidine, cimetidine, amitriptyline, or erythromycin [see Table 18 ] . Do not exceed twice the patient’s usual dose Enzyme (CYP3A) inhibitors Ranitidine 150 mg twice daily 1 mg single dose 1.2 1.4 Dose adjustment not needed Cimetidine 400 mg twice daily 1 mg single dose 1.1 1.3 Dose adjustment not needed Erythromycin 500 mg four times daily 1 mg single dose 1.1 0.94 Dose adjustment not needed Other Drugs Amitriptyline 50 mg twice daily 3 mg twice daily 1.2 1.1 Dose adjustment not Needed *Change relative...
Mechanism: Cimetidine can slightly slow down the enzymes that break down risperidone, but the effect is very small.
Cimetidine and Ranitidine Cimetidine and ranitidine do not affect the clearance of valproate.
Mechanism: Cimetidine does not interfere with how the body breaks down or clears valproate. This means the amount of valproate in your blood should remain stable.
Drugs that Reduce Metformin Clearance Clinical Impact Concomitant use of drugs that interfere with common renal tubular transport systems involved in the renal elimination of metformin (e.g., organic cationic transporter-2 [OCT2] / multidrug and toxin extrusion [MATE] inhibitors such as ranolazine, vandetanib, dolutegravir, and cimetidine) could increase systemic exposure to metformin and may increase the risk for lactic acidosis [see Clinical Pharmacology (12.3) ] .
Mechanism: Cimetidine stops the kidneys from getting rid of metformin as quickly as they should. This can cause metformin to build up in your blood and increase the risk of a serious acid problem.
This is a plain-language summary of FDA-label interaction records and does not provide individual medication-combination directions.
Common Questions
Can I take antacids with cimetidine?
How long does it take for cimetidine to heal an ulcer?
What should I do if I experience confusion while taking cimetidine?
Can cimetidine cause any changes in my hormone levels?
What if I am a heavy smoker with a large ulcer?
How often should I take Cimetidine?
What do I do if I think I am having a side effect?
Can Cimetidine cause issues with my blood?
Does Cimetidine interact with other medications?
Can Cimetidine cause liver problems?
What are the common side effects of cimetidine?
Does cimetidine interact with other medications?
What drug class is cimetidine?
What pregnancy or breastfeeding source fields are listed for cimetidine?
Related Medications in H2 Receptor Antagonist
Other drugs grouped near cimetidine - same-class peers and common alternatives.
alosetron
Lotronex
Alosetron (Lotronex) is a medicine for women with severe diarrhea-predominant irritable bowel syndrome (IBS).
Compare with cimetidine →
aprepitant
Emend
Aprepitant (Emend) is a medicine that helps prevent nausea and vomiting.
Compare with cimetidine →
bisacodyl
Dulcolax
Bisacodyl is a medicine that helps you have a bowel movement.
Compare with cimetidine →
bismuth subsalicylate
Pepto-Bismol
Bismuth subsalicylate (Pepto-Bismol) is a medicine that can treat diarrhea and upset stomach.
Compare with cimetidine →
dexlansoprazole
Dexilant
Dexlansoprazole (Dexilant) is a medicine that lowers stomach acid.
Compare with cimetidine →
Compare beyond drug class
Nationwide peers by FAERS volume & death-report share
Two PlainMeds-derived comparison paths for cimetidine: nearest FDA FAERS report volume and nearest death-report share among drugs with at least 1,000 logged reports, excluding same-class neighbors listed above. Counts reflect reporting volume, not proven individual harm.
Similar FAERS report volume
Nearest drugs by total FAERS reports. This record: 9,140.
Similar death-report share
Nearest drugs by FAERS death-report share. This record: 12.78%.
- warfarin Δ 0.01 pts · 124,873 reports · Vitamin K Antagonist (Anticoagulant) 12.77%death share
- denosumab Δ 0.01 pts · 196,342 reports · RANK Ligand Inhibitor 12.79%death share
- hydrocortisone Δ 0.05 pts · 84,725 reports · Corticosteroid 12.83%death share
- acyclovir Δ 0.07 pts · 109,698 reports · Antiviral (Nucleoside Analog) 12.71%death share
Medication Guides
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Narrow Therapeutic Index Drugs
FDA bioequivalence and label-record context for narrow therapeutic index medicines
Common Drug Interactions
Dangerous medication combinations and how to protect yourself
What the FDA Data Shows for cimetidine
The FDA label for cimetidine (sold under brand names such as Tagamet) classifies it as an over-the-counter product in the H2 Receptor Antagonist class. Cimetidine treats active duodenal ulcers for short periods. Official labeling lists 3 commonly reported side effects, including Headache, Dizziness, Diarrhea.
Post-market surveillance from the FDA Adverse Event Reporting System (FAERS) captures real-world experience. For this drug, FAERS contains 9,140 voluntary reports. The database also lists 77 documented drug interactions derived from FDA labeling, with the top-flagged interaction rated major severity. NADAC pricing from CMS shows a generic unit cost of $0.26.
Report counts do not establish causation, a FAERS entry documents a temporal association, not proof that the drug produced the outcome. Widely prescribed medications naturally accumulate more reports than niche therapies, so raw totals must be interpreted alongside total exposure. Shortage status, recall history, and patent information are separate source-record fields. This page is a public FDA/CMS registry and does not provide medical, treatment, substitution, or medication-change directions.
Data Sources
Drug labeling: FDA Drug Labels (SPL/DailyMed). Adverse events: FDA Adverse Event Reporting System (FAERS). Pricing: CMS National Average Drug Acquisition Cost (NADAC).
FAERS reports are voluntary and do not establish causation. Drug interactions are derived from FDA labeling and clinical references. This registry does not provide medication decisions.
Last updated: August 18, 2023
PlainMeds is rendered directly from FDA openFDA/FAERS extracts, DailyMed labels, and CMS drug-pricing files, no number is typed in by an editor. FAERS counts, recalls, shortages, and price figures on this page are queried live from those federal extracts. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 2026-05-15. Primary sources: openFDA / FAERS, DailyMed and CMS Part B ASP.
Read our methodology - how this data is sourced, computed, and verified.
Data currency: FDA FAERS adverse-event reports through 2025, CMS NADAC acquisition-cost pricing effective December 2024, compiled from the source snapshot dated . See our methodology for per-source dates and refresh cadence. Spot a figure that looks wrong? Report a data issue.
All federal data sources used on this page
- FDA Orange Book - approved drug products with therapeutic equivalence. accessdata.fda.gov/cder/ob
- FDA DailyMed - NIH-hosted drug labeling for FDA-approved meds. dailymed.nlm.nih.gov
- FDA Adverse Event Reporting System (FAERS) - post-marketing safety surveillance. fda.gov/drugs/faers
- NLM RxNorm - standardized clinical drug nomenclature. nlm.nih.gov/research/umls/rxnorm
- CMS Medicare Part B Drug Average Sales Price Files - federal drug pricing data. cms.gov/medicare/part-b-drugs/asp
- FDA Drug Shortages Database - current and resolved drug shortage tracking. accessdata.fda.gov/drugshortages