What is it?
L-tryptophan is one of the essential amino acids, building blocks of protein that the body cannot make and must get from food. The body converts some of it into serotonin, a chemical messenger in the brain. Dietary supplements sell it in much larger doses than food provides, mostly for sleep and mood. In cosmetics it is a minor hair- and skin-conditioning ingredient. Most commercial tryptophan is made by bacterial fermentation.
Key information
- A 1989 epidemic of eosinophilia-myalgia syndrome, which affected about 1,500 people and was linked to more than 30 deaths, was traced to tryptophan supplements from a single Japanese manufacturer.
- An FDA import alert in March 1990 effectively removed tryptophan supplements from the U.S. market until the alert was lifted in 2005.
- Combining tryptophan with antidepressants or other drugs that boost serotonin can, in rare cases, cause serotonin syndrome.
- The CIR Expert Panel concluded in 2012 that tryptophan and other amino acids are safe as used in cosmetics.
More information
Tryptophan for supplements and cosmetics is mostly made by fermentation: bacteria that overproduce the amino acid release it into a sugar-based broth, and it is then separated and crystallized. Labels may call it plant-derived; the molecule is the same either way. The daily requirement is about 5 mg per kilogram of body weight, but some adults take up to 4 to 5 grams a day.
Tryptophan’s reputation comes from 1989, when an epidemic of eosinophilia-myalgia syndrome (EMS), a disabling illness with severe muscle pain and high counts of white blood cells called eosinophils, affected about 1,500 people and was linked to more than 30 deaths. It was traced to supplements from a single Japanese manufacturer that used genetically engineered bacteria; the implicated batches contained more than 60 trace impurities. A 2012 review concluded the cause was a contaminant in certain batches rather than tryptophan itself, although the specific culprit was never confirmed. An FDA import alert in 1990 kept tryptophan supplements off the U.S. market until 2005, and in 2011 researchers described the first clear-cut EMS case they knew of since its return, in a woman taking 1,500 mg a day.
Other side effects, mainly at high doses, include nausea, dizziness and tremor, and rarely serotonin syndrome when tryptophan is combined with drugs that affect serotonin. As a nutrient, L-tryptophan is a permitted U.S. food additive for improving the protein quality of foods. In cosmetics, the Cosmetic Ingredient Review (CIR) Expert Panel concluded in 2012 that it and other amino acids are safe as used; tryptophan was reported in 15 products at no more than 0.0001 percent.
Reality check: the 1989 epidemic was tied to supplements from one producer, not to tryptophan in food or skin care. High-dose supplements are a different exposure, with rare but real risks.
Sources: CIR: Safety Assessment of α-Amino Acids as Used in Cosmetics (final report, 2012); Arthritis & Rheumatism (2011): Post-epidemic eosinophilia-myalgia syndrome associated with L-tryptophan; Journal of Nutrition (2012): Effects and side effects associated with the non-nutritional use of tryptophan by humans; Cornell LII: 21 CFR 172.320, Amino acids
