Is weight gain from effexor (venlafaxine) metabolic?

Not certain: No one is certain as to what causes weight gain on Effexor (venlafaxine) in some patients. For some, Effexor (venlafaxine) might decrease the sense of satiety, or fullness, causing people to eat more than usual. We know that some people have a genetic predisposition to increased side effects to ssris, involving their effect on the serotonin 2a receptor, which has an impact on appetite.