The most commonly reported side effects of phenobarbital include seizure, off label use, and toxicity to various agents, based on 14,877 FDA adverse event reports from 2004 to 2025. 16.1% of reports found the drug to be ineffective.
Percentages show how often each reaction appears relative to total reports for phenobarbital.
These are voluntary reports and do not establish that phenobarbital caused these reactions.
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Other drugs that appear in adverse event reports alongside phenobarbital. 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.
46.9% of phenobarbital adverse event reports involve female patients and 39.5% involve male patients. The largest age group is adult at 46%. These figures reflect who reports side effects, not underlying risk.
Sex
Age group
Conditions and purposes for which patients were taking phenobarbital when the adverse event was reported.
Showing 15 of 523 indications
Phenobarbital is sold under the brand name Sezaby.
An upward trend reflects increased FAERS reporting overall, not necessarily increased risk.
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