Quick answer

L-tryptophan is an essential amino acid the body uses to make protein, serotonin, melatonin and niacin. US adults already eat about 826 mg a day, roughly three times their need. As a supplement, early evidence links 1 g or more a day to less time awake at night, and anyone on a serotonin medicine should ask first.^1,2,3

Key facts

The body cannot make tryptophan, so it has to come from food.¹
Fewer than 1 percent of US adults fall short of the average requirement.⁴
About 60 mg of tryptophan is counted as equal to 1 mg of niacin.⁵
The labels of sertraline, escitalopram, fluoxetine and trazodone all list tryptophan as a serotonergic drug to be careful with.^6,7,8,9

What L-tryptophan does in the body

Tryptophan is an essential amino acid: the body cannot make it, so it has to come from food.¹

The body uses tryptophan to build proteins and to make serotonin and melatonin, and the liver can turn it into niacin (vitamin B3) when there is enough iron, riboflavin and vitamin B6.¹

Getting into the brain is competitive. Tryptophan competes with other large amino acids for entry, so a meal full of protein brings plenty of competition along with it. A tryptophan supplement taken on its own avoids that, which is why it raises the brain's tryptophan and its serotonin production in a way that food does not.^10,11

About 60 mg of tryptophan is generally counted as equal to 1 mg of niacin; a study of young women on a controlled diet estimated about 67 mg.⁵

What the evidence shows

Both claims below are graded early. The sleep finding comes from four pooled trials, and the mood finding from a review in which 4 of 11 trials found a difference.^3,12

May reduce time spent awake during the night, at 1 g or more a day*^3,13

Early evidence

A 2022 meta-analysis pooled four trials and found that tryptophan shortened the time people spent awake after first falling asleep, with a larger effect at 1 g a day or more than at lower amounts. It did not change the other parts of sleep that were measured. NIH's center for complementary health says it is unclear how tryptophan works and describes the data as very limited.

Amount studied: 1 g or more a day; smaller amounts had less effect

May help maintain a positive mood in healthy adults*^12,14

Early evidence

A 2021 systematic review found 11 randomized trials of tryptophan in healthy adults, at 0.14 to 3 g a day on top of usual meals. Four of them found less negative feeling or more happy feeling than in the comparison group, and no effect was found on aggressive feelings. A separate three-week trial in 17 healthy young women found no change in mood scores at 1 to 5 g a day.

Amount studied: 0.14 to 3 g a day, in addition to usual meals

NIH's center for complementary health says tryptophan supplements have sedative effects but that it is unclear how they work.¹³

How much you need and how much you eat

Tryptophan is found in cheese, milk, egg whites, chicken, turkey, fish, soybeans, peanuts, and pumpkin, sunflower and sesame seeds.¹

Adults need about 4 to 5 mg of tryptophan per kg of body weight a day: 4 mg is the average requirement, and a 2012 review gives 5 mg. For a 70 kg adult, that is about 280 to 350 mg.^2,11

US adults typically take in about 826 mg of tryptophan a day from food.²

That gap means a tryptophan supplement is rarely about filling a shortfall. People take it in amounts far above the need, usually hoping to change sleep or mood, and some take 4 to 5 g a day.^4,11

What's in ours

What’s in ours

Sleep: L-Tryptophan, 100 mg per serving, from the label

Our Sleep formula lists 100 mg of L-tryptophan per serving. That is a tenth of the 1 g at which the night waking effect was clearest and about an eighth of what US adults eat in a day, so its product page makes no claim for tryptophan.^2,3

Medicines, side effects and what happened in 1989

Avoid the combination unless your doctor advises it

The label of phenelzine, an MAOI antidepressant, tells people taking it not to take L-tryptophan: it lists it with compounds that can trigger a dangerous rise in blood pressure with MAOIs, and among the over-the-counter products to avoid. It also says MAOIs combined with tryptophan have been reported to cause disorientation, confusion, agitation, shivering, unsteadiness and other nervous system effects.¹⁵

On the medicine's label

Ask your pharmacist or doctor first

The sertraline label lists tryptophan among the serotonergic drugs that raise the risk of serotonin syndrome when taken with sertraline, and tells prescribers to monitor for it. MedlinePlus names tryptophan among the nonprescription products that may interact with sertraline, and NIH warns that L-tryptophan taken with medicines that affect serotonin may cause life-threatening serotonin toxicity.^6,13,16

On the medicine's label

Avoid the combination unless your doctor advises it

The escitalopram label says using it with tryptophan is not recommended, because the combination raises the risk of serotonin syndrome. MedlinePlus also lists tryptophan among the nonprescription products that may interact with escitalopram.^7,13,17

On the medicine's label

Ask your pharmacist or doctor first

The fluoxetine and trazodone labels carry the same warning: tryptophan is among the serotonergic drugs that raise the risk of serotonin syndrome with them, and MedlinePlus lists tryptophan as a product that may interact with trazodone. Not every antidepressant's label names tryptophan, so ask about yours.^8,9,18

On the medicine's label

Combined with medicines that raise serotonin, tryptophan can contribute to serotonin syndrome, a rare reaction that can be life-threatening. Warning signs include agitation, confusion, hallucinations, sweating, fever, shivering, a fast heartbeat, muscle twitching or stiffness and loss of coordination.^6,11,13,16

Side effects reported with tryptophan supplements are occasional, mild and short-lived: drowsiness, nausea, dizziness and tremor, mostly at high doses of 70 to 200 mg per kg.¹¹

In 1989, contaminated L-tryptophan from a single manufacturer caused an outbreak of eosinophilia-myalgia syndrome in the US, with 1,536 cases and 27 deaths reported by August 1990. The illness brought severe, disabling muscle pain and a very high count of eosinophils, a type of white blood cell, and the use of L-tryptophan as a supplement was stopped.^13,19

We found no official upper limit for tryptophan supplements, and researchers say a thorough dose-by-dose safety assessment has not been done. In one trial, 17 healthy young women took up to 5 g a day for 21 days with no adverse effects on the measures checked.^11,14

Ask first if you take any medicine that affects serotonin: antidepressants, triptans for migraine, tramadol, lithium, buspirone or St. John's wort.⁶
Ask first if you are pregnant or nursing, or under 18.

Questions people ask

Does L-tryptophan help you sleep?

The evidence is early. Pooled trials found less time awake during the night at 1 g a day or more, but no change in the other parts of sleep measured, and NIH's center for complementary health calls the data very limited.^3,13

What is the difference between L-tryptophan and 5-HTP?

5-HTP is a separate supplement. Both are substances the body can change into melatonin, but the label warnings and safety notes on this page are about L-tryptophan.¹³

Does L-tryptophan work differently in men?

No research we found looked at men separately. In a 2026 study of adults over 60, men and women needed the same amount per kg of body weight.²⁰

Is L-tryptophan a treatment for chronic insomnia?

No. NIH's center for complementary health says there is very limited data on tryptophan for insomnia, and the American Academy of Sleep Medicine's 2017 guideline recommends against using it for chronic insomnia. Poor sleep that lasts for weeks is worth a visit to a doctor.¹³

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Sources

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.