Does eating turkey really make people drowsy? This urban legend has been passed down and cited for years, partially thanks to Americans’ tendencies to lapse into a food-and-football coma after Thanksgiving dinner. But while turkey does contain the ingredient tryptophan—a chemical known for its sleep-inducing properties—it’s no more likely to send you off to dreamland than any other large meal.

Tryptophan is an essential amino acid, which means humans don’t produce it internally and must get it from plant and animal sources. It is credited with helping bring about healthy sleep and a stable mood. Tryptophan is found in turkey, chicken, eggs, milk, cheese, fish, soy, nuts, seeds, and legumes—but it works best on an empty stomach, so the type present in food is not a very effective sleep aid.

The dietary supplement L-tryptophan, on the other hand, has been shown to increase levels of serotonin in the brain and help treat insomnia in some patients. L-tryptophan supplements have also been studied for the treatment of premenstrual dysphoric disorder, attention deficit disorder, and seasonal affective disorder, and for smoking cessation, although results have been mixed.

In 1990, contaminated L-tryptophan supplements manufactured in Japan caused an outbreak of eosinophilia-myalgia syndrome, an illness that can cause muscle pain and death, and their sale was banned by the Food and Drug Administration until 2002. Today, tryptophan is available in health food and vitamin stores and is also sold as a prescription drug (Tryptan) often used with antidepressants.

L-tryptophan is considered safe when taken as directed, but it can interact with herbs such as St. John’s wort and drugs that induce sleepiness, such as alcohol, cold medicines, pain medications, muscle relaxants, and medications for depression or anxiety.

ADDITIONAL FACTS

  1. In the body, tryptophan is converted into the substances niacin and serotonin.
  2. The disorder fructose malabsorption syndrome causes improper absorption of tryptophan in the intestine, reduced levels of tryptophan in the blood, and depression.
  3. There have been no published cases of eosinophilia-myalgia syndrome within the past several years, but people who take L-tryptophan should be aware of its symptoms, including severe muscle pain; weakness, numbness, or burning sensations, especially at night; and dryness, yellowing, or hardening of the skin.