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5-HTP and tryptophan are both precursors to serotonin, the body’s most well-known mood neurotransmitter. Tryptophan is an essential amino acid, meaning it has to be acquired from the diet, and 5-HTP can be made within the human system, but it depends on the presence of tryptophan for its conversion. Both substances can be found in the natural environment, but are often times supplemented because tryptophan is a relatively rare amino acid, found only in small amounts in foods such as bananas and turkey, and the only readily available source of 5-HTP is from Griffonias simplicifolia, a bean from western Africa. Orthodox conversion of serotonin begins with a quantity of tryptophan, which is acted upon by an enzyme, tryptophan hydroxylase, and becomes 5-HTP. Another enzyme, tryptophan decarboxylase, as well as vitamin B6 are then needed to convert 5-HTP to 5-HT, which is serotonin.
As serotonin cannot cross the blood brain barrier (BBB) effectively, the majority of the neurotransmitter has to be made within the confines of the brain. This requires the presence of either 5-HTP or tryptophan. Tryptophan has to compete with five other amino acids for transport across the BBB, while 5-HTP has significantly less competition and crosses the BBB with less effort. Sometimes, this leads to 5-HTP being favored as a supplement to increase serotonin. Another advantage that the human system gains from converting 5-HTP, instead of tryptophan, is that 5-HTP is not degraded by the enzyme tryptophan pyrolase, a process that sometimes inhibits adequate production of serotonin from tryptophan.
Both 5-HTP and tryptophan can be taken to promote the production of serotonin within the system. Tryptophan became popular in the 1970s when the American health food industry began to tout it as a supplement. It was available over-the-counter, and many people took the supplement to treat depression and other disorders, like premenstrual syndrome (PMS) and insomnia.
Tryptophan use was even more widespread in European countries. The Food and Drug Administration (FDA) banned the sale of tryptophan as a supplement in the US because a tainted batch of the substance from Japan caused many cases of a rare and sometimes serious condition, eosinophilia myalgia. Within the US, tryptophan is available only by prescription and can only be made in a compounding pharmacy. It is still sold over-the-counter in Europe.
Studies pertaining to the use of 5-HTP and tryptophan are encouraging. With the ban of tryptophan within the US, clinical studies using 5-HTP have increased. Both 5-HTP and tryptophan have been shown to be as effective as some allopathic anti-depressant medications.