I've just switched from Prozac to Effexor about a month ago. I've lost 5 lbs. in the last two weeks. My appetite has greatly diminished. I'm 25 lbs. overweight so I'm happy about this side effect. I also lost weight the first year I was on Prozac. I lost about 40 lbs. Then I just stopped losing weight. I've been at the same weight for about a year. Maybe now I'll get this last 20 lbs. off. Even better than the weight loss, Effexor has improved my depression!!