What the label lists and what reports show
Methenamine side effects
Methenamine's FDA label lists its adverse reactions in its own words. FAERS holds 1,210 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 diarrhoea (81 reports).
- Generic listed
Check it at the source: the methenamine FDA label on DailyMed (effective August 7, 2026, ANI Pharmaceuticals, Inc.); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsMinor adverse reactions have been reported in less than 3.5% of patients treated. These reactions have included nausea, upset stomach, dysuria, and rash. To report SUSPECTED ADVERSE REACTIONS, contact ANI Pharmaceuticals, Inc. at 1-855-204-1431 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.
Source: FDA drug label, ANI Pharmaceuticals, Inc., effective August 7, 2026 (SPL set a3eeacd4-1983-49ec-a60d-3abaf505ce57), via openFDA; the full label on DailyMed
What do FAERS reports show?
1,210 reports list methenamine among the medicines taken, each a report of something that happened, not proof the medicine caused it; 75 are coded as a death and 335 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 19 reactions below, 2 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?
- Methenamine: 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