In clinical studies, a number of side effects were reported with Effexor. Weight change was reported as a possible side effect. At least 1 percent of people who took the
antidepressant experienced weight gain.
Weight gain appears to be a much more common side effect of Effexor. On average, people lose about one to two pounds when they begin taking this medication. However, it is also possible for people to lose large amounts of weight. Although weight loss may be a desirable side effect for some people, too much weight loss can be a problem.