one of the main neurotransmitters. Serotonin belongs to monoamines, as do norepinephrine, dopamine, and histamine. Monoamines not only maintain homeostasis but also regulate behavior. More precisely, the function of serotonin can be described as facilitating homeostasis through counteracting disruptions in metabolic cycles. The serotonergic system is closely connected with functions involved in the regulation of mood, sleep, sexual behavior, and eating behavior.