The most commonly reported side effects of trimethoprim include off label use, pyrexia, and fatigue, based on 106,772 FDA adverse event reports from 2004 to 2025. 4.0% of reports found the drug to be ineffective.
Percentages show how often each reaction appears relative to total reports for trimethoprim.
These are voluntary reports and do not establish that trimethoprim caused these reactions.
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Other drugs that appear in adverse event reports alongside trimethoprim. Drugs flagged as a suspected cause appear in the first column. Drugs taken at the same time but not suspected appear in the second.
Also suspected
Taken alongside
Co-occurrence in adverse event reports does not establish a drug interaction. Patients often take multiple medications, and these lists reflect prescribing patterns rather than causal relationships. Consult a healthcare provider about potential drug interactions.
46.8% of trimethoprim adverse event reports involve female patients and 44.0% involve male patients. The largest age group is adult at 52%. These figures reflect who reports side effects, not underlying risk.
Sex
Age group
Conditions and purposes for which patients were taking trimethoprim when the adverse event was reported.
Showing 15 of 1,756 indications
Trimethoprim is sold under brand names including Sulfamethoprim, Trimethoprim Sulfate And Polymyxin B Sulfate, Primsol.
An upward trend reflects increased FAERS reporting overall, not necessarily increased risk.
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