A side effect of many psychotropic drugs is weight change, particularly weight gain. The drugs most likely to contribute to weight gain are: among neuroleptics, chlorpromazine, clozapine and olanzapine; among antidepressants, amitriptyline and mirtazapine; and among mood stabilisers, valproic acid derivatives. It was also noted that drugs such as fluoxetine, isocarboxazide, nefazodone, topiramate and psychostimulants may cause weight loss. When making therapeutic decisions, it is worth taking these data into account.