Unintended increase in body weight following use of certain medications. The precise mechanism is complex, and involves metabolic, hormonal, behavioral, and appetite changes. Unintended progressive weight gain can contribute to dyslipidemia, insulin resistance, obesity, and the increased risk of cardiovascular disease and diabetes.

Medications associated with weight gain include antipsychotics (especially second generation antipsychotics such as clozapine and olanzapine), antidepressants (lithium, amitriptyline, clomipramine, imipramine, doxepin, trimipramine, and some SSRIs), antidiabetics (pioglitazone, rosiglitazone), anticonvulsants (carbamazepine, valproic acid, gabapentin, and pregabalin with thiazolidinedione), and hormonal therapy.

Management of medication-induced weight gain includes patient education, weight-maintenance diet, physical activity, exploration of alternative medications, and dosage adjustment. Metformin has been found to help reduce weight gain caused by certain medications.