Belviq (generic: lorcaserin) is a prescription weight loss medicine used to treat obese or overweight adults who have at least one medical problem related to their weight. It is believed that Belviq decreases appetite and makes you feel full faster by binding to, and activating certain serotonin receptors in the brain. Serotonin is a neurotransmitter, a chemical in the brain, that has various functions. These include the regulation of mood, appetite, sleep, as well as other functions.