URL of this page: https://medlineplus.gov/druginfo/natural/326.html


What is it?

L-tryptophan is an amino acid. Amino acids are protein building blocks. L-tryptophan is called an "essential" amino acid because the body can't make it on its own. It must be acquired from food. L-tryptophan is eaten as part of the diet and can be found in protein-containing foods.

People use L-tryptophan for severe PMS symptoms (premenstrual dysphoric disorder or PMDD), athletic performance, depression, insomnia, and many other conditions, but there is no good scientific evidence to support these uses.

How effective is it?

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 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 L-tryptophan by mouth doesn't help reduce this type of 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 L-tryptophan during exercise doesn't improve endurance during a cycling exercise. 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, L-tryptophan 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.
  • Fibromyalgia. Early research shows that adding walnuts to a Mediterranean diet to provide extra L-tryptophan and magnesium might improve anxiety and some other symptoms of fibromyalgia.
  • 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 L-tryptophan might also improve sleep in people with sleep problems related to withdrawal of illegal drugs.
  • Migraine. Early research has found that having low levels of L-tryptophan in the diet is linked to an increased risk of migraine.
  • Severe PMS symptoms (premenstrual dysphoric disorder or PMDD). Taking 6 grams of L-tryptophan per day seems to decrease mood swings, tension, and irritability in women with PMDD.
  • 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 with a certain form of this condition, called obstructive sleep apnea (OSA).
  • Quitting smoking. Taking L-tryptophan along with conventional treatment might help some people to quit smoking.
  • Anxiety.
  • Decline in memory and thinking skills in older people that 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.

How does it work?

L-tryptophan is naturally found in animal and plant proteins. L-tryptophan is considered an essential amino acid because our bodies can't make it. It is important for the development and functioning of many organs in the body. After absorbing L-tryptophan from food, our bodies convert some of it to 5-HTP (5-hyrdoxytryptophan), and then to serotonin. Our bodies also convert some L-tryptophan to niacin (vitamin B3). Serotonin is a hormone that transmits signals between nerve cells. It also causes blood vessels to narrow. Changes in the level of serotonin in the brain can alter mood.

Are there safety concerns?

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 headache, lightheadedness, drowsiness, dry mouth, visual blurring, muscle weakness, and sexual problems in some people. In 1989, L-tryptophan 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 L-tryptophan 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 L-tryptophan is safe when taken by mouth long-term.

Special precautions & warnings:

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 breast-feeding. Stay on the safe side and avoid L-tryptophan during pregnancy and breast-feeding.

Are there interactions with medications?

Do not take this combination.
Sedative medications (CNS depressants)
L-tryptophan might cause sleepiness and drowsiness. Medications that cause sleepiness are called sedatives. Taking L-tryptophan along with sedative medications might cause too much sleepiness.

Some sedative medications include clonazepam (Klonopin), lorazepam (Ativan), phenobarbital (Donnatal), zolpidem (Ambien), and others.
Be cautious with this combination.
Serotonergic drugs
L-tryptophan increases a chemical in the brain called serotonin. Some medications also increase serotonin. Taking L-tryptophan along with these medications might increase serotonin too much. This can cause serious side effects including severe headache, heart problems, shivering, confusion, and anxiety.

Some of these medications include fluoxetine (Prozac), paroxetine (Paxil), sertraline (Zoloft), amitriptyline (Elavil), clomipramine (Anafranil), imipramine (Tofranil), sumatriptan (Imitrex), zolmitriptan (Zomig), rizatriptan (Maxalt), methadone (Dolophine), tramadol (Ultram), and many others.

Are there interactions with herbs and supplements?

Herbs and supplements with sedative properties
L-tryptophan can cause drowsiness and relaxation. Using it along with other herbs and supplements that also have sedative effects might cause too much drowsiness. Some of these herbs and supplements include 5-HTP, calamus, California poppy, catnip, hops, Jamaican dogwood, kava, St. John's wort, skullcap, valerian, yerba mansa, and others.
Herbs and supplements with serotonergic properties
L-tryptophan seems to raise the level of serotonin, a hormone that transmits signals between nerve cells and affects mood. There is a concern that using it with other herbs and supplements that increase serotonin, might increase the effects and side effects of those herbs and supplements. Some of those include 5-HTP, Hawaiian baby woodrose, and S-adenosylmethionine (SAMe).
St. John's wort
Combining L-tryptophan with St. John's wort might increase the risk of serotonin syndrome, a possibly fatal condition that occurs when there is too much serotonin in the body. There is a report of serotonin syndrome in a patient who took L-tryptophan and high doses of St. John's wort.

Are there interactions with foods?

There are no known interactions with foods.

What dose is used?

Some dietary supplement products might not list L-tryptophan separately on the label. Instead, it might be listed under niacin. Niacin is measured in niacin equivalents (NE). 60 mg of L-tryptophan is the same as 1 mg NE.

The appropriate dose of L-tryptophan depends on several factors such as the user's age, health, and several other conditions. At this time there is not enough scientific information to determine an appropriate range of doses for L-tryptophan. Keep in mind that natural products are not always necessarily safe and dosages can be important. Be sure to follow relevant directions on product labels and consult your pharmacist or physician or other healthcare professional before using.

Other names

L-Triptofano, L-Trypt, L-2-amino-3-(indole-3-yl) propionic acid, L-Tryptophane, Tryptophan.


To learn more about how this article was written, please see the Natural Medicines Comprehensive Database methodology.


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Last reviewed - 09/09/2020