In humans, serotonin is a neurotransmitter used throughout the body having action of 14 variants of the serotonin receptor to have diverse effects on mood, anxiety, sleep, appetite, temperature, eating behaviour, sexual behaviour, movements, and gastrointestinal motility. Serotonin is not administered clinically as a drug itself as it is not specific enough. However, drugs that selectively target specific serotonin receptor subtypes are used therapeutically for antidepressant effects; these are called selective serotonin re-uptake inhibitors. They are dependent on serotonin availability in the synapse.