Mysimba is a prescription weight loss treatment for people who are overweight and comes as a tablet that is taken once or twice every day. Unlike other weight loss tablets, which work by changing how your body stores fat, Mysimba works by suppressing your appetite.Mysimba is a prescription weight loss treatment for people who are overweight and comes as a tablet that is taken once or twice every day. Unlike other weight loss tablets, which work by changing how your body stores fat, Mysimba works by suppressing your appetite.