Serotonin is a neurotransmitter that is released by nerve endings and cells in the central nervous system in the brain. Serotonin is responsible for regulating moods and plays a critical role in the reward functions of the nervous system itself. Serotonin is regulated by molecules that bind to 5 HT2 receptors in the brain, and it is made in the raphe nucleus, located in the brainstem. Many psychedelic drugs regulate serotonin levels to cause their psychoactive effects. Some of the most common drugs involved in this process include psilocybin, mescaline, and LSD. Serotonin is also a common target of mental health treatments and therapies.