According to reports from clinical trials, most people tolerate L-tryptophan supplements without side effects. Occasionally, dizziness, stomach pain, and diarrhea have been reported.211
Until 1989, L-tryptophan was a popular nutritional supplement used for a variety of conditions.212 In that year, the US Food and Drug Administration removed L-tryptophan from the over-the-counter supplement market, citing the outbreak of an unusual ailment called eosinophilia-myalgia syndrome (EMS) that was associated with its use.213 Since then, researchers have determined that the most likely cause of this syndrome was a contaminant produced by a single manufacturer during the process of L-tryptophan production that was not effectively removed.214, 215 Contamination errors have long since been corrected, and today L-tryptophan is again available as a supplement.
Two case reports suggested that a supplement containing L-tryptophan might have caused a scleroderma-like syndrome that resembled EMS in some ways.216, 217 However, the supplement in one case contained a very small amount of L-tryptophan, and it also contained other ingredients.218 Larger surveys of people with scleroderma have found no link with L-tryptophan supplementation,219, 220 so it is likely that these two cases were either a coincidence or it could be a contamination issue.
The safety of taking L-tryptophan during pregnancy and breast-feeding is unclear. In a double-blind trial, the breathing activity of fetuses was temporarily altered when pregnant women took one gram of L-tryptophan.221 The relevance of that change to fetal health needs further study. In hamsters, supplementation with L-tryptophan during pregnancy decreased the litter size and increased the mortality of the offspring.222
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The information presented in Aisle7 is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. Self-treatment is not recommended for life-threatening conditions that require medical treatment under a doctor's care. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires June 2015.