It has been suggested 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 likely caused by a contaminant in certain 5-HTP supplements. Production 5-HTP is produced from the amino acid tryptophan through the action of the enzyme tryptophan hydroxylase. Tryptophan hydroxylase is one of the biopterin-dependent aromatic amino acid hydroxylases. Production of 5-HTP is the rate-limiting step in 5-HT synthesis. 5-HTP is normally rapidly converted to 5-HT by amino acid decarboxylase. Absorption After oral administration, 5-HTP is absorbed by the upper intestine. The mode of absorption is not known, but presumably involves active transport via amino acid transporters. 5-HTP is adequately absorbed via oral cavity. With a decarboxylase inhibitor, the bioavailability of 5-HTP can be higher than 50%. Pharmacokinetics 5-HTP is rapidly absorbed with Tmax of ~1.5h, and rapidly eliminated with a half-life of ~1.5–2 h. Co-administration of a decarboxylase inhibitor (e.g. carbidopa, benserazide) doubles the half-life of 5-HTP, to 3–4 h, and enhances exposure several fold, depending on the dosing regimen. Metabolism 5-HTP 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. Other studies have indicated the risk of a scleroderma-like condition resulting from the combination of 5-HTP and carbidopa. Regulatory status There are currently no approved drug products containing 5-HTP approved by the FDA. All available 5-HTP products are nutraceuticals and are as such not regulated or verified for purity, integrity, or clinical efficacy or safety, mandating caution regarding human consumption. As of 25 August 2020, Hungary added 5-HTP to the controlled psychoactive substances list, prohibiting production, sale, import, storage and use, becoming the first country to do so. 5-HTP slow-release 5-HTP's short half-life is impractical for chronic drug therapy. Research conducted at Duke University in mice have demonstrated that 5-HTP when administered as slow-release appears to gain drug properties. Slow-release delivery attenuates or abolishes the peaks and valleys in 5-HTP exposure during