cimetidine
Brand names: Tagamet
Cimetidine (Tagamet) reduces stomach acid. It is used to treat ulcers, heartburn, and other conditions where too much acid is produced.
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.
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.
How to Take It
Take cimetidine exactly as your doctor tells you to. For duodenal ulcers, you might take it once a day at bedtime, or several times a day with meals and at bedtime. Do not take antacids at the same time as cimetidine, as they can interfere with absorption. Continue taking cimetidine for as long as your doctor recommends, even if you start feeling better.
Pregnancy & Breastfeeding
Tell your doctor if you are pregnant or plan to become pregnant. The effects of cimetidine during pregnancy are not fully known. Talk to your doctor about the risks and benefits of taking cimetidine while breastfeeding.
Missed Dose
If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and continue with your regular schedule.
Storage
Store cimetidine tablets at room temperature (68° to 77°F) and protect them from light.
Side Effects (from patient reports)
Based on 6,312 FDA adverse event reports.
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
Death-Related Reports
1,168
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 |
| 6 | DRUG INEFFECTIVE | 504 |
| 7 | DYSPNOEA | 504 |
| 8 | VOMITING | 483 |
| 9 | DIARRHOEA | 440 |
| 10 | PAIN | 432 |
| 11 | DEATH | 399 |
| 12 | DIZZINESS | 386 |
| 13 | OFF LABEL USE | 377 |
| 14 | HEADACHE | 371 |
| 15 | GASTROOESOPHAGEAL REFLUX DISEASE | 370 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: FDA FAERS (Adverse Event Reporting System) 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.
What to do: No dosage changes are needed, so you can safely take these medications together as prescribed.
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.
What to do: Avoid taking these two medicines together unless your doctor determines that the benefits are greater than the risks.
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 t...
Mechanism: Cimetidine can slightly slow down the enzymes that break down risperidone, but the effect is very small.
What to do: No dose changes are needed when taking these two medicines together.
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.
What to do: You can take these medications together without needing to change your dose. Your doctor will continue to monitor you as usual.
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.
What to do: Your doctor may need to monitor you more frequently or adjust your medication levels.
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?
Is cimetidine safe during pregnancy?
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 →
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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 6,312 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 further shape supply and switching decisions. This page summarizes public FDA data for educational purposes only and is not a substitute for professional medical advice — always consult a licensed healthcare provider before starting, stopping, or changing any medication.
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. Always consult a healthcare professional before making medication decisions.
Last updated: August 18, 2023
Read our methodology — how this data is sourced, computed, and verified.
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