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What is the most important information I should know about L-tryptophan?

L-tryptophan is sold as a dietary supplement and is not subject to U.S. Food and Drug Administration (FDA) guidelines for safe manufacturing. Some of the L-tryptophan sold in the U.S. is imported from manufacturers in other countries. The FDA has not determined the safety, purity, or effectiveness of L-tryptophan. All of the potential risks and benefits of using this product are therefore unknown.

Dietary supplements and herbal "medicines" may contain toxic or impure ingredients that could be harmful to your health. Dietary and herbal supplements should be purchased from a reliable source such as a pharmacy or well-known retail store. Do not use any dietary or herbal product that does not list a manufacturer and/or distributor name and address on the label.

In 1989, a life-threatening condition called eosinophilia-myalgia syndrome (EMS) occurred in many people using L-tryptophan and some died from the condition. All of these people had taken L-tryptophan distributed by a company in Japan. This L-tryptophan was found to contain trace levels of impure ingredients. Since that time, the FDA has limited the availability of L-tryptophan in the U.S. However, the increased use of the Internet has made many dietary supplements available from non-U.S. sources.

There have been no published cases of EMS within the last several years, but you should be aware of the symptoms. Stop using L-tryptophan and call your doctor or care practitioner at once if you have any of these signs of EMS: severe muscle pain (most often in the shoulders, back, or legs); weakness, numbness, tingling, or burning pain (especially at night); tremors or twitching muscle movements; swelling in any part of your body; skin changes (dryness, yellowing, hardening); breathing difficulty; uneven heartbeat.

Less serious side effects are more likely to occur. Talk to your doctor or care practitioner about any side effect that seems unusual or that is especially bothersome.

Other drugs may interact with L-tryptophan. Tell your doctor or care practitioner about all the prescription and over-the-counter medications you use. This includes vitamins, minerals, herbal products, and drugs prescribed by other doctors. Do not start using a new medication without telling your doctor or care practitioner.

Stop using L-tryptophan and get emergency medical help if you think you have used too much of the product, or if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.