What medications cause weight gain?

Several big drug families list weight gain as a known effect, and knowing yours is on the list changes the conversation from personal failure to pharmacology. MedlinePlus names weight gain among the most common side effects of antidepressants, and the wider list from prescribing references includes: antipsychotics, which shift appetite and metabolism; corticosteroids like prednisone, especially at higher doses over weeks; insulin and some diabetes drugs, which push calories into storage; some beta-blockers; certain seizure and migraine preventives; older antihistamines used daily; and some hormonal treatments. The mechanisms differ: increased appetite, slowed metabolism, fluid retention, and reduced activity from sedation all contribute depending on the drug. What to do if the scale moves after a new medicine: do not stop it, because the conditions these drugs treat are usually more dangerous than the pounds; do track the timeline, since weight gain that tracks the start date is the tell; bring it to the prescriber specifically, because within most drug families there are weight-friendlier alternatives, and sometimes a dose change or add-on strategy works; and treat the lifestyle countermeasures as real medicine, protein-forward meals, walking after meals, and sleep, since the drug tilts the playing field and habits tilt it back. A gain of a few pounds is usually manageable; a rapid gain over a few weeks deserves a prompt appointment.