FDA scientists have confirmed the presence of impurities in some 5-hydroxy-L-tryptophan (5HTP) products currently marketed and widely promoted as dietary supplements. These products are being used as aids for insomnia, depression, obesity, and in children with attention deficit disorder. FDA's analytical results are consistent with those obtained and published by researchers from the Mayo Clinic.

FDA took action to limit the availability of L-tryptophan supplements because of the association between dietary supplements containing L-tryptophan and the 1989 epidemic outbreak of eosinophilia-myalgia syndrome (EMS) in the United States. In the summer and fall of 1989, an epidemic outbreak of eosinophilia-myalgia (EMS) occurred in the United States.