L-Tryptophan Benefits: What the Research Says

L-tryptophan is one of the building blocks of protein, and it’s sold as a supplement for sleep, mood and even growth hormone. So what are the real L-tryptophan benefits? Here’s what the studies actually show, how strong that evidence is, and what to know about safety before you try it.

Summary

The best-supported L-tryptophan benefits are modest: a small pooled analysis found that 1 gram or more a day may cut the time spent awake during the night, but it didn’t improve other sleep measures. Large single doses do raise growth hormone briefly, and a few small exercise studies disagree with each other. Evidence for depression is thin and old, and supplements need extra care if you take antidepressants.

What is L-tryptophan?

Tryptophan is an essential amino acid, which means your body can’t make it, so it has to come from food [1]. Your body uses it to build proteins, and to make serotonin (a brain chemical thought to help regulate mood, appetite, sleep and pain), melatonin (a hormone that helps run your sleep-wake cycle) and niacin (vitamin B3) [1]. “L-tryptophan” is simply the form found in food and in most supplements.

Good food sources include cheese, chicken, egg whites, fish, milk, peanuts, pumpkin and sesame seeds, soybeans and turkey [1]. The amount you need from your diet is modest: about 5 mg per kilogram of body weight a day, or roughly 350 mg for a 70 kg (154 lb) adult [2]. Supplement users often take far more, up to 4–5 grams a day, usually hoping to improve mood or sleep [2].

Does L-tryptophan increase growth hormone?

Large single doses can, but only briefly and not by much. In fact, doctors once used a big oral dose of tryptophan as a test of how the body releases growth hormone (GH), not as a way to boost it.

In a 1982 Finnish study, 8 healthy men took 2, 5 or 8 grams of L-tryptophan, or a placebo (a dummy pill), in random order [3]. All three doses raised blood GH from about 2 ng/mL (nanograms per milliliter) to peaks of roughly 7–9 ng/mL, while the placebo caused only a small rise (about 2 to 3 ng/mL) that wasn’t statistically significant [3]. The three doses didn’t differ significantly from each other, though the 8-gram dose tended to work less well. In a larger group of 24 men given 5 grams, about 1 in 5 didn’t respond at all, and two drugs used in GH testing (L-dopa and apomorphine) were stronger GH triggers [3]. An earlier 1974 study described tryptophan’s effect on GH as only “slight” [4].

Just as important, a short GH spike isn’t the same as building muscle or burning fat. We found no study testing whether tryptophan’s GH bump does either. (We cover the same question for other amino acids in our post on lysine and arginine.)

L-tryptophan and exercise: mixed results

There’s a theory that tryptophan could actually add to tiredness during long exercise. In a 1988 study of 22 marathon runners, the amount of “free” tryptophan in the blood (the part not attached to the blood protein albumin) rose about 2.4-fold during the race, while branched-chain amino acids (BCAAs, which compete with tryptophan to get into the brain) fell [5]. The researchers suggested this could raise serotonin in the brain and contribute to physical or mental fatigue, but that was a hypothesis, not something they measured [5].

Supplement studies point in different directions:

• A positive result: In a 1988 study of 12 healthy sportsmen running on a treadmill at 80% of their VO₂max (their maximum oxygen use, a measure of fitness), they lasted 49.4% longer after L-tryptophan than after a placebo [6]. They also rated the effort as a bit easier, though that difference wasn’t statistically significant. The authors thought tryptophan might have raised pain tolerance [6].
• A failed repeat: Because such a big jump is rare in sports research, Norwegian researchers repeated the idea in 49 well-trained male runners, using the same total dose (1.2 grams over 24 hours) in a randomized, double-blind trial (neither the runners nor the researchers knew who got what) [7]. This time the runners ran at 100% of VO₂max, and tryptophan made no significant difference [7].
• A small cycling study: In 20 young sportsmen doing a cycling test that mixed steady riding with short all-out sprints, double-blind and in random order, power output (how much work they produced on the bike) was higher with L-tryptophan than with placebo, and they covered about 5% more distance in the final 20 minutes (12,526 vs 11,959 meters) [8].

That’s three studies with conflicting results: two small positive ones from the same Spanish research group [6, 8], and a larger, well-designed negative one [7]. It’s not enough to say L-tryptophan improves performance.

L-tryptophan benefits for sleep

Sleep is where the evidence is most encouraging, though still limited. A 2022 meta-analysis (a study that pools the results of earlier studies) collected 18 articles but could only combine the data from 4 of them [9]. Tryptophan supplements shortened “wake after sleep onset,” the time spent awake after first falling asleep, and doses of 1 gram or more a day worked better than smaller doses [9]. But tryptophan didn’t improve the other sleep measures the researchers looked at [9].

Food may play a part too. In a small Australian study of 12 healthy young men, a high-glycemic-index rice meal (one that raises blood sugar quickly) eaten 4 hours before bed cut the time it took to fall asleep from about 17.5 to 9 minutes, compared with a low-glycemic-index rice meal [10]. Eating it just 1 hour before bed worked less well, and no other sleep measures changed [10]. The researchers point out that carbohydrate-rich meals are known to raise blood tryptophan, but this study tested meals, not tryptophan supplements, and its results still need testing in people with sleep problems [10].

If sleep is your goal, you may also want to read our posts on melatonin and ZMA.

Does L-tryptophan help with mood or depression?

Because tryptophan is used to make serotonin, it has long been tried for depression. But a 2002 systematic review (a structured search and summary of all the studies on a question) by Australian researchers found 108 studies, and only 2, with 64 patients in total, were good enough to include [11]. Those two suggested tryptophan or a related compound, 5-hydroxytryptophan (5-HTP, the step between tryptophan and serotonin), worked better than placebo, but the authors said the studies were too small, and too many others were poorly done, to judge whether these supplements really work [11].

In a small 2013 trial in healthy young women, doses up to 5 grams a day for 3 weeks didn’t change mood scores [12]. Depression is a serious medical condition, so please don’t use L-tryptophan in place of treatment, and talk to your doctor before combining it with any medicine (see safety below).

How much L-tryptophan do people take?

There’s no official recommended supplement dose. In the sleep meta-analysis, doses of 1 gram or more a day looked more helpful than lower doses [9]. Supplement users take up to 4–5 grams a day [2].

The best safety data for these higher doses comes from a Japanese trial in 17 healthy women aged 18 to 26 [12]. Each woman took a placebo and 1, 2, 3, 4 and 5 grams a day for 21 days each, double-blind and in random order. No dose affected food intake, body weight, routine blood and urine tests or mood [12]. That’s reassuring, but it’s a small, short study in young, healthy women.

L-tryptophan side effects and safety

A 2012 review of tryptophan’s use as a supplement found that side effects are usually occasional, mild and short-lived, but it also said the data is small and mostly anecdotal [2]. Things to know:

• Occasional side effects: drowsiness (which some people want, if they take it for sleep), plus tremor, nausea and dizziness, seen mainly at higher doses [2].
• Serotonin syndrome: In rare cases, taking tryptophan with medicines that boost serotonin, such as antidepressants, can cause serotonin syndrome, a dangerous overload of serotonin activity. Symptoms include confusion, muscle jerks, high body temperature and, in severe cases, coma [2]. Don’t combine tryptophan with antidepressants or other serotonin-affecting medicines unless your doctor says it’s OK.
• The 1989 EMS outbreak: In 1989, a new illness called eosinophilia-myalgia syndrome (EMS) appeared, marked by severe muscle pain and a high level of a type of white blood cell (eosinophils). By August 1990, the US Centers for Disease Control (CDC) had received reports of 1,536 cases and 27 deaths, almost all in people who had taken L-tryptophan products, and the FDA began recalling tryptophan supplements in November 1989 [13]. A Minnesota investigation found that 29 of 30 patients whose source was known had taken tryptophan from one manufacturer (compared with 60% of healthy users), and linked the illness to changes in how that company made it [14]. A 2012 review concluded the cause was a contaminant in certain batches rather than tryptophan itself [2], but a 2023 review (written partly by staff of a company that makes amino acids) says studies of the suspected impurities haven’t reached a clear conclusion [15].

Because the outbreak was tied to how one company made its tryptophan [14], product quality matters. We found no safety studies of tryptophan supplements in pregnancy or breastfeeding, so talk to your doctor first if you’re pregnant or breastfeeding, take any prescription medicine, or have a medical condition.

The bottom line on L-tryptophan benefits

The most promising L-tryptophan benefit is a small improvement in staying asleep at doses of about 1 gram or more a day, based on only a handful of studies. Large doses raise growth hormone briefly, but there’s no evidence this builds muscle. Exercise studies conflict, and the evidence for depression is too weak to rely on. The amount you need from food is modest [2]. If you do try a supplement, avoid combining it with antidepressants and check with your doctor first.

This article is for general information only and isn’t medical advice. Talk to your doctor or another qualified health professional before starting a new supplement. See our medical disclaimer.

References

1. MedlinePlus Medical Encyclopedia. Tryptophan. US National Library of Medicine. Reviewed April 30, 2026. https://medlineplus.gov/ency/article/002332.htm
2. Fernstrom JD. Effects and side effects associated with the non-nutritional use of tryptophan by humans. J Nutr. 2012;142(12):2236S-2244S. doi:10.3945/jn.111.157065
3. Koulu M. Re-evaluation of L-tryptophan-stimulated human growth hormone secretion: a dose-related study with a comparison with L-dopa and apomorphine tests. J Neural Transm. 1982;55(4):269-275. doi:10.1007/BF01243448
4. Müller EE, Brambilla F, Cavagnini F, Peracchi M, Panerai A. Slight effect of L-tryptophan on growth hormone release in normal human subjects. J Clin Endocrinol Metab. 1974;39(1):1-5. doi:10.1210/jcem-39-1-1
5. Blomstrand E, Celsing F, Newsholme EA. Changes in plasma concentrations of aromatic and branched-chain amino acids during sustained exercise in man and their possible role in fatigue. Acta Physiol Scand. 1988;133(1):115-121. doi:10.1111/j.1748-1716.1988.tb08388.x
6. Segura R, Ventura JL. Effect of L-tryptophan supplementation on exercise performance. Int J Sports Med. 1988;9(5):301-305. doi:10.1055/s-2007-1025027
7. Stensrud T, Ingjer F, Holm H, Strømme SB. L-tryptophan supplementation does not improve running performance. Int J Sports Med. 1992;13(6):481-485. doi:10.1055/s-2007-1021302
8. Javierre C, Segura R, Ventura JL, Suárez A, Rosés JM. L-tryptophan supplementation can decrease fatigue perception during an aerobic exercise with supramaximal intercalated anaerobic bouts in young healthy men. Int J Neurosci. 2010;120(5):319-327. doi:10.3109/00207450903389404
9. 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;80(2):306-316. doi:10.1093/nutrit/nuab027
10. Afaghi A, O’Connor H, Chow CM. High-glycemic-index carbohydrate meals shorten sleep onset. Am J Clin Nutr. 2007;85(2):426-430. doi:10.1093/ajcn/85.2.426
11. 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;36(4):488-491. doi:10.1046/j.1440-1614.2002.01046.x
12. Hiratsuka C, Fukuwatari T, Sano M, Saito K, Sasaki S, Shibata K. Supplementing healthy women with up to 5.0 g/d of L-tryptophan has no adverse effects. J Nutr. 2013;143(6):859-866. doi:10.3945/jn.112.173823
13. Centers for Disease Control. Update: eosinophilia-myalgia syndrome associated with ingestion of L-tryptophan — United States, through August 24, 1990. MMWR. 1990;39(34):587. https://www.cdc.gov/mmwr/preview/mmwrhtml/00001738.htm
14. Belongia EA, Hedberg CW, Gleich GJ, et al. An investigation of the cause of the eosinophilia-myalgia syndrome associated with tryptophan use. N Engl J Med. 1990;323(6):357-365. doi:10.1056/NEJM199008093230601
15. Ko SM, Park JE, Heo IK, Shin YU, Kim YH, Son WC. Safety concerns regarding impurities in L-tryptophan associated with eosinophilia myalgia syndrome. Food Chem Toxicol. 2023;179:113946. doi:10.1016/j.fct.2023.113946