In clinical studies, weight gain was reported as a common side effect of
trazodone hydrochloride (Desyrel®), occurring in up to 4.5 percent of people taking the drug. Interestingly, weight loss was also a commonly reported side effect, occurring in up to 5.7 percent of people taking the antidepressant.
It is not entirely clear why these weight changes can occur while taking trazodone. However, it is possible that, for weight loss, other side effects of trazodone may play a role, including nausea, loss of appetite, and diarrhea.