Tryptophan is an amino acid; one of the 20 found in the basic genetic code: codon UGG. It is essential in human nutrition, and may have significant effects on the human brain.
Tryptophan is a precursor for serotonin, melatonin, and niacin. In those who cannot metabolize it properly, it's possible that tryptophan is a cause of schizophrenia. Improperly metabolized, its waste products are toxic to the brain and cause hallucinations and delusions. However, it's also been found to aid schizophrenic patients.
Tryptophan is produced by the human body, but can also be found in many sources of dietary protein, including chocolate, oats, bananas, dried dates, cottage cheese, red meat, fish, milk, peanuts, and most famously turkey.
According to a widespread myth, when the tryptophan in turkey is consumed, it is supposed to make the person consuming it very sleepy within a matter of hours. Whether this is fact or not is doubtful, especially the uniqueness of turkey. Still, tryptophan supplements have been used as a safe and somewhat effective sleep aid. This effect is probably because of its ability to increase brain levels of serotonin and melatonin. Serotonin is known for its calming effects, and melatonin, secreted by the pineal gland when dark or low light levels predominate, induces slumber.
According to clinical research, tryptophan does act reasonably well as a sleep inducer, an antidepressant, and an augmentor of antidepressants. Chronic pain and reduction of negative extreme behaviors (impulsivity, mania, addiction, etc.) has also been indicated by researchers. And it may be effective in treating seasonal-affective disorder, or SAD.
However, due to an outbreak of eosinophilia-myalgia syndrome (a sometimes-deadly autoimmune disease) traced to taking tryptophan from Japan, tryptophan supplements were banned by numerous companies. The problem was ultimately identified as probably a contaminant and not tryptophan at all, but the health agencies of many countries still remain leery of tryptophan.
Despite this, psychiatrists continue to prescribe tryptophan as an antidepressant by itself or, more often, as an augmentor for other antidepressants in patients who are unresponsive to antidepressants.
Web Resources On Tryptophan
Stanford Study on Tryptophan
The Calming Effects of Tryptophan
Book Resources On Tryptophan
Lysine, Tryptophan and Other Amino Acids by Robert Garrison Jr.
Tryptophan: Biochemical and Health Implications by Herschel Sidransky