L-Tryptophan Benefits: What the Evidence Shows

Quick answer

L-tryptophan benefits, in short: L-tryptophan is an amino acid your body uses to make serotonin, a chemical involved in mood and sleep. A meta-analysis of 4 trials found that tryptophan, especially at 1 g or more a day, shortened the time people spent awake after falling asleep, but other sleep measures did not change [1]. For mood, small trials in healthy adults suggest a lift in some studies [2], while the evidence in people with depression is too weak to rely on [3]. One case report describes a dangerous reaction when it was taken with antidepressants [5]. We rate the evidence C: mixed results and a small evidence base.

What is L-tryptophan?

Tryptophan is an essential amino acid, which means your body can’t make it and you must get it from food. It is a building block for serotonin and, in turn, melatonin. Supplements usually contain L-tryptophan on its own, sometimes in doses of a gram or more. That is a different product from 5-HTP, a related compound, which is not covered here.

L-tryptophan benefits: what might it help with?

Possible benefit	Rating	In plain words
Sleep (time awake after falling asleep)	Promising	A shorter time awake in a meta-analysis of 4 trials, mainly at 1 g or more [1]
Other sleep measures	No clear benefit	Tryptophan did not change other sleep components [1]
Mood in healthy adults	Mixed	4 of 11 trials showed benefits, and results varied [2]
Depression	Early	Only 2 trials (64 people) were good enough to count, which is too few to judge [3]

Ratings describe how good the research is, not a promise that it will work for you.

What the research says

• Sleep (4 trials in the analysis). Tryptophan shortened the time awake after sleep onset (about 81 minutes less for each gram of tryptophan). People taking 1 g or more did better than those taking under 1 g. Other sleep components did not change [1]. PubMed · DOI
• Mood in healthy adults (11 trials). Four trials found less anxiety and more positive mood, and none found a benefit for aggressive feelings. The authors suggested 0.14 to 3 g a day, noting that the best dose and timing are unclear [2]. PubMed · DOI
• Depression. A review found 108 studies, but only 2 trials with 64 people (one on 5-HTP, one on L-tryptophan) were good enough to include. They favored the supplements, but the authors said the studies were too small and poorly done to judge effectiveness [3]. This review is old (it searched up to 2000). PubMed · DOI
• Safety history. A rare condition called eosinophilia-myalgia syndrome was linked in the past to some tryptophan supplements. A later review says the cause is still uncertain, with impurities from manufacturing suspected but no clear conclusion [4]. PubMed · DOI
• Serotonin syndrome. One published case report describes serotonin syndrome, which can look like a seizure, in a person who took tryptophan together with two antidepressant medicines [5]. We could read only the title of this report. PubMed · DOI

The key limits: the sleep and mood analyses pooled few, small trials and used different doses. Nothing here shows tryptophan improves long-term health.

Amounts and how people take it

These are amounts used in studies, not recommendations.

• Sleep: the analysis compared under 1 g with 1 g or more a day; the larger amount did better on time awake [1].
• Mood: 0.14 to 3 g a day alongside normal meals [2].

Side effects, interactions and who should check first

We did not find reliable data on common side effects. The main concern we found is a case report of serotonin syndrome when tryptophan was combined with antidepressants [5]. The earlier link with eosinophilia-myalgia syndrome is described as unresolved [4].

Who should check with a doctor or pharmacist first

Check with a doctor or pharmacist first if you:

• take any antidepressant or other medicine that affects serotonin. Taking tryptophan alongside them may cause serotonin syndrome [5]
• take any other regular medicine, because we found no verified interaction list
• are pregnant or breastfeeding, as we found no verified safety data
• have a long-term health condition, or depression or anxiety. Don’t use tryptophan to replace treatment you’ve been prescribed
• are under 18

Where to buy

Availability varies by country; in England, supplements are limited to 220 mg per daily dose, otherwise sold only through a pharmacist or hospital [6].

Look for the active form and amount (L-tryptophan, in mg per serving), a stated third-party testing certificate you can check, and work out the price per daily dose rather than comparing pack prices.

FAQ

What is L-tryptophan?

L-tryptophan is an essential amino acid, which means your body can’t make it and you must get it from food. Your body uses it to make serotonin, a chemical involved in mood, and melatonin. Supplements usually contain L-tryptophan on its own. That is a different product from 5-HTP, a related compound that this page does not cover.

Does L-tryptophan help with sleep?

A meta-analysis of 4 trials found it shortened the time people spent awake after falling asleep, especially at 1 g or more a day, but other sleep measures did not change [1]. The analysis pooled few, small trials. Nothing here shows tryptophan improves long-term health. We rate the evidence C.

How much L-tryptophan per day?

For sleep, the analysis compared under 1 g with 1 g or more a day, and the larger amount did better on time awake [1]. For mood in healthy adults, studies used 0.14 to 3 g a day alongside normal meals, and the best dose and timing are unclear [2]. These are amounts used in studies, not recommendations.

Is L-tryptophan safe?

We found no reliable data on common side effects. The main concern is a case report of serotonin syndrome when tryptophan was combined with two antidepressants [5], so ask a doctor or pharmacist first if you take any antidepressant or other medicine that affects serotonin. An older link with eosinophilia-myalgia syndrome is described as unresolved [4].

Can you take L-tryptophan with alcohol?

We found no study of L-tryptophan with alcohol, so we can’t say whether the combination is safe. The interaction we did find is with antidepressants and other medicines that affect serotonin [5]. Don’t use tryptophan in place of care you’ve been prescribed, and ask a doctor or pharmacist first if you take any medicine.

Related pages

• L-theanine
• Magnesium
• Glycine
• Longevity supplements for beginners: where this fits in a beginner’s routine
• All supplements A-Z

Talk to your doctor

This page is for general information and is not medical advice. Speak to a doctor or pharmacist before starting any supplement, especially if you are pregnant or breastfeeding, take any medicine, or have a health condition.

References

We cite only studies and official pages we checked against PubMed, the publisher or the agency’s own site. The A to E evidence grades are explained in our editorial policy. See also our medical disclaimer and affiliate disclosure.

1. Sutanto CN, Loh WW, Kim JE. The impact of tryptophan supplementation on sleep quality: a systematic review, meta-analysis, and meta-regression. Nutr Rev. 2022. PubMed · DOI
2. Kikuchi AM, Tanabe A, Iwahori Y. A systematic review of the effect of L-tryptophan supplementation on mood and emotional functioning. J Diet Suppl. 2021. PubMed · DOI
3. Shaw K, Turner J, Del Mar C. Are tryptophan and 5-hydroxytryptophan effective treatments for depression? A meta-analysis. Aust N Z J Psychiatry. 2002. PubMed · DOI
4. Ko SM, Park JE, Heo IK, et al. Safety concerns regarding impurities in L-Tryptophan associated with eosinophilia myalgia syndrome. Food Chem Toxicol. 2023. PubMed · DOI
5. Ambarapu S, Tilwe K, Pandit RA, et al. Serotonin Syndrome Masquerading as Status Epilepticus following Ingestion of Tranylcypromine and Clomipramine and L-Tryptophan: A Case Report. Ann Indian Acad Neurol. 2022. PubMed · DOI
6. UK Statutory Instruments. The Tryptophan in Food (England) Regulations 2005, SI 2005/2630, regulations 4 and 5. legislation.gov.uk