Serotonin molecule. Computer artwork of a molecule of serotonin (5hydroxytryptamine, C10.H12.N2.O), a neurotransmitter. Atoms (spheres) are colour coded: carbon (black), hydrogen (white), nitrogen (blue) and oxygen (red). Serotonin is an important neurotransmitter in the brain, and a lack of it has been shown to cause depression. It is this property which has led to the development of the SSRI (selective serotonin reuptake inhibitor) antidepressants, such as Prozac (fluoxetine). The hormone melatonin is made from serotonin in the brains pineal gland. Serotonin is also released by blood platelets during clot formation, when it causes the constriction of blood vessels.