Prozac weight gain is generally not a problem. In fact, the opposite is true. You are more likely to drop pounds without even trying. The medication is really powerful for the treatment of depression and other mental issues. Weight gain would be the least of your worries. Prozac is notorious for causing users to think about and possibly act upon suicidal thoughts. In addition, taking this medication can have potentially fatal results, if combined with other drugs. For example, if you take MAOIs already, and then add Prozac, you can develop serotonin syndrome, which means there is too much of it in your system. If this happens to you, the hospital is where you need to be, so doctors can closely observe as the serotonin levels go down.