The most commonly reported side effects of phentermine include general physical health deterioration, dyspnoea, and dizziness, based on 32,778 FDA adverse event reports from 2004 to 2025. 2.9% of reports found the drug to be ineffective.
Percentages show how often each reaction appears relative to total reports for phentermine.
These are voluntary reports and do not establish that phentermine caused these reactions.
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Other drugs that appear in adverse event reports alongside phentermine. 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.
58.8% of phentermine adverse event reports involve female patients and 32.1% involve male patients. The largest age group is elderly at 52%. These figures reflect who reports side effects, not underlying risk.
Sex
Age group
Conditions and purposes for which patients were taking phentermine when the adverse event was reported.
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An upward trend reflects increased FAERS reporting overall, not necessarily increased risk.
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