One of the most talked about "hormones" is serotonin. Serotonin is linked to many aspects of behavior, and influences pineal function. Serotonin, as a brain neurotransmitter, appears in several forms and attaches to numerous receptors in the brain and gut. Serotonin works in a relatively fixed way in each individual, baring drug use.

The amino acid 5-HTP (5-hydroxy-tryptophan) is a precursor to serotonin that converts to tryptophan. Tryptophan in turn converts to 5HT-serotonin, and finally to 5HIAA metabolic serotonin and the hormone melatonin - thus serotonin is relevant to pineal function and sleep as well as its own functions.

Physical effects of Serotonin: High levels of serotonin constrict blood vessels and bronchial tubes, stimulate a strong heartbeat, and affect blood clotting. High serotonin is also associated with migraines because it constricts blood vessels or causes the blood vessels to spasm. High serotonin also inhibits ejaculation in men. Hyperserotonemia (dangerously elevated serotonin) is linked to serious medical complications and neurological and psychiatric disorders. One is Carcinoid syndrome, caused by serotonin releasing tumors. Symptoms flushing of the skin lasting from minutes to days, diarrhea, bronchial constriction, sudden blood pressure loss, and fluid retention in the abdomen.

Behavioral effects of Serotonin: Besides the various forms of serotonin, there are at least fifteen different kinds of receptors for serotonin in the brain alone, making it responsible for a broad variety of behaviors in ways that can vary individually. Thus high or low serotonin levels can manifest in somewhat different ways in people, with many different kinds of behavioral states:

• affection, empathy, sociability, intimacy and interpersonal responsiveness, cheerful out-going behavior, and peaceful contentment (high 5HIAA)
• compliance and obedience to authority (high 5HIAA)
• aggression, violence, resistance and hostility to authority, anxiety, impulsive action without concern of punishment, impaired employment, and argumentativeness (low 5HIAA)
• promiscuity, exhibitionism, and aberrant sexual behavior (low 5HIAA)
• suicide (often violent) and depression (low 5HIAA)
• alcohol and substance abuse and substance addiction (low 5HIAA)
• confusion of dreams and reality, hypnotic suggestibility and trance states, sleep-like brain wave patterns even when awake, nightmares and sleepwalking, insomnia
• schizophrenia, psychosis, and mania, altered perception, childhood mental retardation and autism, Alzheimer's disease and senile dementia (high 5HT)
• anorexia (high 5HP) and bulimia (low 5HIAA)

Anti-depressants such as the drug Prozac artificially raise 5HT serotonin levels by inhibiting the removal of serotonin after it is made. And higher 5HIAA serotonin is effective for eliminating the behaviors associated with Attention Deficit Disorder. Ideally, balanced serotonin levels translate to confidence about life, reduced pain, and a sense of aliveness with mental clarity. However, because of individual biological variation and the fact of various serotonin forms, receptors, and effects, there is an element of unpredictability that can lead to positive or negative effects.

Serotonin and the Gut: Finally, there are also many serotonin receptors in the gut. Thus, one’s mood (one’s emotional temperament) affects one’s digestion - with food contributing to a feeling of well being. Dieting lowers serotonin. Weight-gain raises it. People often feel better and more sociable after eating because of the natural rise in serotonin levels. Anti-depressants such as Prozac tend to disrupt digestion when used for prolonged periods.