Yes, I agree on the serotonin. SSRIs are known to cause (often quite substantial) weight gain in many people. Interestingly, though, some people initially experience weight loss on SSRIs, so the weight gain may be more of a longterm issue. There was a 60-week study on Prozac in which patients lost weight compared to placebo at first, but then in the 2nd half of the study began gaining weight. This all makes me wonder what the long-term outcomes of Belviq will be. The fact that the woman quoted in the article had rebound weight gain isn’t the most promising sign.