5-Hydroxytryptophan

5-Hydroxytryptophan (5-HTP), also known as oxitriptan (INN), is a naturally occurring amino acid and chemical precursor as well as a metabolic intermediate in the biosynthesis of the neurotransmitters serotonin and melatonin from tryptophan.

5-HTP is sold over the counter in the United Kingdom, United States and Canada as a dietary supplement for use as an antidepressant, appetite suppressant, and sleep aid, and is also marketed in many European countries for the indication of major depression under trade names like Cincofarm, Levothym, Levotonine, Oxyfan, Telesol, Tript-OH, and Triptum. Several double-blind placebo-controlled clinical trials have demonstrated the effectiveness of 5-HTP in the treatment of depression, though a lack of high quality studies has been noted. More and larger studies are needed to determine if 5-HTP is truly effective in treating depression, but funding for such studies is lacking due to its non-patentable status.

Metabolism
5-Hydroxytryptophan is decarboxylated to serotonin (5-hydroxytryptamine or 5-HT) by the enzyme aromatic-L-amino-acid decarboxylase with the help of vitamin B6. This reaction occurs both in nervous tissue and in the liver. 5-HTP crosses the blood–brain barrier, while 5-HT does not. Excess 5-HTP, especially when administered with Vitamin B6, is thought to be metabolized and excreted.

Pharmacology
The psychoactive action of 5-HTP is derived from its increase in production of serotonin in central nervous system tissue.



Research shows that co-administration with carbidopa greatly increases plasma 5-HTP levels. However, several studies have reported that 5-HTP is effective even without a peripheral decarboxylase inhibitor (e.g. carbidopa). Other studies have indicated the risk of a scleroderma-like condition resulting from the combination of 5-HTP and carbidopa.

Dietary sources
Though 5-HTP is found in food only in insignificant quantities, it is a chemical involved intermediately in the metabolism of tryptophan, an amino acid found in milk, meat, potatoes, pumpkin, and various greens. See also the section Dietary sources of the article on L-tryptophan.

Therapeutic use
5-HTP is sold over-the-counter in the United States, the United Kingdom, and Canada as a dietary supplement for use as an antidepressant, appetite suppressant, and sleep aid. 5-HTP in supplement form is typically sold in 50 mg or 100 mg gelatin or vegetarian capsules. It is usually sourced from the seeds of Griffonia simplicifolia.

5-HTP has been studied and shown to be of benefit in the following conditions: primary fibromyalgia syndrome, Friedreich's ataxia, anxiety, binge eating associated with obesity, and insomnia. There is no statistically significant difference between 5-HTP and placebo in treating chronic headaches (primary or otherwise).

In 2001 a Cochrane Review of the effect of 5-HTP and tryptophan on depression was published. The authors included only studies of a high rigor and included both 5-HTP and tryptophan in their review because of the limited data on either. Of 108 studies of 5-HTP and tryptophan on depression published between 1966 and 2000, only two met the authors' quality standards for inclusion, totaling 64 study participants. The substances were more effective than placebo in the two studies included but the authors state that, "the evidence was of insufficient quality to be conclusive," and note, "because alternative antidepressants exist which have been proven to be effective and safe, the clinical usefulness of 5-HTP and tryptophan is limited at present."

5-HTP is often taken by people coming down from MDMA to relieve post-MDMA dysphoria. The basis for doing this is that 5-HTP is a necessary precursor for the brain to produce more serotonin, and MDMA use depletes a person's natural serotonin levels, thus taking 5-HTP after consuming MDMA is speculated as helping improve serotonin production. While the practice is common, the theory is physiologically reasonable, and anecdotal evidence is widespread, no scientifically verifiable evidence can currently be found to confirm whether the practice actually works. Concurrent use of 5-HTP and serotonin releasers such as MDMA increases the risk of serotonin syndrome; a possibly fatal condition.

Possible risks or side effects
Because 5-HTP has not been thoroughly studied in a clinical setting, possible side effects and interactions with other drugs are not well known. However, it is noteworthy that no published reports of serious side effects (from non-contaminated 5-HTP) exist, despite that 5-HTP is freely available as a nutraceutical. This could indicate that serious side effects are relatively rare with 5-HTP, at least in moderate doses. On the other hand, acute moderate gastrointestinal effects, such as diarrhea and vomiting, are common upon administration of 5-HTP, probably due to rapid formation of serotonin in the upper intestinal tract.

Oral 5-HTP results in an increase in urinary 5-HIAA, a serotonin metabolite, indicating that 5-HTP is peripherally metabolized to serotonin, which is then metabolized. This might cause a false positive test in tests looking for carcinoid syndrome.

Known drug interactions:

In humans 5-HTP has never been clinically associated with serotonin syndrome.
 * When combined with antidepressants of the MAOI or SSRI class, high dose 5-HTP can cause acute serotonin syndrome in rats.

It has been suggested by the pharmaceutical industry that 5-HTP may cause eosinophilia-myalgia syndrome (EMS), a serious condition which results in extreme muscle tenderness, myalgia, and blood abnormalities. However, there is evidence to show that EMS was caused by a contaminant in early 5-HTP supplements, before the introduction of the current Good Manufacturing Practices by the United States FDA in 2007. Many countries now employ similar regulation.
 * When combined with carbidopa (as a treatment for symptoms of Parkinson's disease), 5-HTP causes nausea and vomiting; however this can be alleviated via administration of granisetron. As mentioned above under pharmacology, cases of scleroderma-like illness have been reported in patients using carbidopa and 5-HTP.