No, I didn't gain weight. I'm a guy, maybe that is why, we seem to have high metabolisms. But then I'm pretty active and work out too. Not a big eater per se. I think it is an SSRI but you could look it up on the web to make sure. It's worked so well for me I almost forget what it is and how it works. I can tell you my doc' and I had been working on my symptoms a long time and I finally went to him and said, "I'm going to die, I just can't go on." That's when he started trying Paxil, Welbutin and finally Effexor that worked. No idea why the others didn't. Believe it or not, once the symptoms went away I had to relearn "real" symptoms like muscels that ached from simply hiking! Before the normal aches and pains were masked by the debilitating symptoms of chronic fatigue. I'll have to take it the rest of my life but it saved my life.