Antidepressants are the first-line treatment choice for depression. However， most antidepressants have many adverse reactions， including cardiac metabolic effects and weight gain. Antidepressants have different risks of weight gain， and there are differences in the same category of antidepressants. Current research results show that histamine and serotonin play a key role in adverse reactions of weight gain， beyond the previously thought ways of promoting appetite. Therefore， paying attention to the side effect of weight gain is an important factor in choosing antidepressants. This article reviews the mechanism of the effect of commonly used antidepressants on body weight.