Natural Medicines Comprehensive Database rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, Ineffective, and Insufficient Evidence to Rate. The effectiveness ratings for L-TRYPTOPHAN are as follows:

Possibly effective for…

  • Severe PMS symptoms (premenstrual dysphoric disorder or PMDD). Taking 6 grams per day seems to decrease mood swings, tension, and irritability in women with PMDD.
  • Quitting smoking. Taking L-tryptophan seems to help people quit smoking when used with conventional treatment.

Possibly ineffective for…

  • Teeth grinding (bruxism). Taking L-tryptophan by mouth doesn’t help treat teeth grinding.
  • A condition that causes persistent muscle pain (myofascial pain syndrome). Taking it by mouth doesn’t help reduce persistent muscle pain.

Insufficient evidence to rate effectiveness for…

  • Athletic performance. Some research shows that taking L-tryptophan for 3 days before exercising can improve power during exercise. This improvement in power helps increase the distance an athlete can go in the same amount of time. But other early research shows that taking it during exercise doesn’t improve endurance during a cycling exercise. The reasons for the conflicting results are not clear. It is possible that L-tryptophan improves some measures of athletic ability but not others. On the other hand, it might need to be taken for a few days before exercise in order to see any benefit.
  • Attention deficit-hyperactivity disorder (ADHD). There is some evidence that L-tryptophan levels are lower in children with ADHD. But taking L-tryptophan supplements does not appear to improve ADHD symptoms.
  • Depression. Early research suggests that L-tryptophan might improve the effectiveness of common medications for depression.
  • A digestive tract infection that can lead to ulcers (Helicobacter pylori or H. pylori). Research shows that taking L-tryptophan in combination with the ulcer medication omeprazole improves ulcer healing rates compared to taking omeprazole alone.
  • Insomnia. Taking L-tryptophan might decrease the amount of time it takes to fall asleep and improve mood in healthy people with sleep problems. Taking it might also improve sleep in people with sleep problems related to withdrawal of illegal drugs.
  • Seasonal depression (seasonal affective disorder or SAD). Early research suggests L-tryptophan might be helpful in SAD.
  • A sleep disorder in which people temporarily stop breathing while asleep (sleep apnea). There is some evidence that taking L-tryptophan might decrease episodes in some people who periodically stop breathing during sleep (sleep apnea).
  • Anxiety.
  • The decline in memory and thinking skills in older people is more than what is normal for their age.
  • Gout.
  • Premenstrual syndrome (PMS).
  • Tourette syndrome.
  • Other conditions.

More evidence is needed to rate L-tryptophan for these uses.

Side Effects Of L-Tryptophan

  • When taken by mouth: L-tryptophan is POSSIBLY SAFE when taken by mouth, short-term. L-tryptophan can cause some side effects such as heartburn, stomach pain, belching and gas, nausea, vomiting, diarrhea, and loss of appetite. It can also cause headaches, lightheadedness, drowsiness, dry mouth, visual blurring, muscle weakness, and sexual problems in some people. In 1989, it was linked to over 1500 reports of eosinophilia-myalgia syndrome (EMS) and 37 deaths. EMS is a neurological condition that causes many different symptoms. These symptoms tend to improve over time, but some people may still experience symptoms up to 2 years after they develop EMS. In 1990, L-tryptophan was recalled from the market due to these safety concerns. The exact cause of EMS in patients taking it is unknown, but some evidence suggests it is due to contamination. About 95% of all EMS cases were traced to L-tryptophan produced by a single manufacturer in Japan. Currently, under the Dietary Supplement Health and Education Act (DSHEA) of 1994, L-tryptophan is available and marketed as a dietary supplement in the United States.

There isn’t enough reliable information to know if it is safe when taken by mouth long-term.

Warnings & Precautions

  • Pregnancy and breast-feeding: L-tryptophan is LIKELY UNSAFE in pregnancy because it may harm the unborn child. There isn’t enough reliable information to know if L-tryptophan is safe to use when breastfeeding. Stay on the safe side and avoid L-tryptophan during pregnancy and breast-feeding.

Dosage Of L-Tryptophan

The following doses have been studied in scientific research:



  • For severe PMS symptoms (premenstrual dysphoric disorder or PMDD): 6 grams of L-tryptophan have been taken daily from ovulation to the third day of the period.
  • For quitting smoking: 50 mg/kg of L-tryptophan have been taken daily.


Consult your doctor or pharmacist.


All information has been provided courtesy of MedLinePlus from the National Library of Medicine and from the FDA.