What the label lists and what reports show
Cimetidine side effects
Cimetidine's FDA label lists its adverse reactions in its own words. FAERS holds 9,664 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is chronic kidney disease (1,318 reports).
- Generic listed
Check it at the source: the cimetidine FDA label on DailyMed (effective July 15, 2026, Mylan Pharmaceuticals Inc.); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsAdverse effects reported in patients taking cimetidine tablets are described as follows by body system. Incidence figures of 1 in 100 and greater are generally derived from controlled clinical studies. Gastrointestinal Diarrhea (usually mild) has been reported in approximately 1 in 100 patients. CNS Headaches, ranging from mild to severe, have been reported in 3.5% of 924 patients taking 1,600 mg/day, 2.1% of 2,225 patients taking 800 mg/day and 2.3% of 1,897 patients taking placebo. Dizziness and somnolence (usually mild) have been reported in approximately 1 in 100 patients on either 1,600 mg/day or 800 mg/day. Reversible confusional states, e.g., mental confusion, agitation, psychosis, depression, anxiety, hallucinations, disorientation, have been reported predominantly, but not exclusively, in severely ill patients. …
Source: FDA drug label, Mylan Pharmaceuticals Inc., effective July 15, 2026 (SPL set 06c0a509-026f-44e0-9975-a94a8de51d43), via openFDA; the full label on DailyMed
What do FAERS reports show?
9,664 reports list cimetidine among the medicines taken, each a report of something that happened, not proof the medicine caused it; 1,206 are coded as a death and 3,539 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 22 reactions below, 6 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Cimetidine: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions