L-tryptophan is an essential amino acid that your body converts into serotonin and then melatonin. In trials, doses of one gram or more have shortened the time it takes people with mild sleep problems to fall asleep (Hartmann, 1982). The evidence at lower doses, such as the 200mg found in UK supplements, is thin.
This article explains the pathway, the research, and why UK products contain the amount they do.
What is L-tryptophan?
Tryptophan is one of the nine essential amino acids, meaning you have to get it from food. It is found in protein-rich foods including oats, milk, cheese, tuna, chicken, turkey, peanuts and bananas (Richard et al., 2009).
Most people get plenty. American adults average about 826mg a day, against an estimated requirement of around 4mg per kilogram of body weight, or roughly 280mg for a 70kg adult (Lieberman, Agarwal and Fulgoni, 2016).
From tryptophan to melatonin
Inside the body, tryptophan is converted to 5-HTP and then to serotonin. The first step is the bottleneck: the enzyme that performs it is only about half saturated at normal tryptophan levels, so supplying more tryptophan can increase serotonin production (Richard et al., 2009). Tryptophan is also the starting material for melatonin (Committee on Toxicity, 2004).
This is why tryptophan is called a precursor. It gives the body raw material and leaves it to make its own signalling molecules.
Why what you eat with it matters
To reach the brain, tryptophan has to cross the blood-brain barrier, and it shares its transporter with several other amino acids. What counts is the ratio of tryptophan to those competitors in the blood.
Classic experiments in rats showed that a carbohydrate meal raised brain tryptophan and serotonin, while a protein meal did not, even though protein contains more tryptophan (Fernstrom and Wurtman, 1972). In people, the tryptophan ratio in blood was 54% higher after a carbohydrate-rich breakfast than a protein-rich one (Wurtman et al., 2003).
In practical terms, tryptophan taken away from a large protein meal faces less competition.
What the research says about tryptophan and sleep
The classic trials
Most tryptophan sleep research dates from the 1970s and 1980s. A review of 40 controlled studies concluded that one gram or more increases sleepiness and shortens the time taken to fall asleep, with the clearest results in people with mild insomnia. Results were mixed or negative in normal sleepers and in people with severe insomnia (Hartmann, 1982).
A later review found that tryptophan helped younger people with situational insomnia from the first night at doses of 1 to 15g, with no sign of tolerance (Schneider-Helmert and Spinweber, 1986).
Not every trial agreed:
- In 96 people with serious insomnia, 1g a night for a week did not outperform placebo during treatment (Hartmann, Lindsley and Spinweber, 1983).
- In 18 women with trouble falling asleep, 1g was no different from placebo, and 3g helped only on some nights (Brown, Horrom and Wagman, 1979).
The modern meta-analysis
A 2022 meta-analysis found that tryptophan supplementation reduced the time people spent awake after first falling asleep. It did not find an effect on other aspects of sleep (Sutanto, Loh and Kim, 2022).
What about low doses?
One study tested doses within the range of a normal diet. In 15 people with mild insomnia, 1g significantly shortened the time to fall asleep. Doses of 250mg and 500mg produced a trend in the same direction that did not reach significance, though 250mg did increase deep sleep (Hartmann and Spinweber, 1979).
That is the main direct evidence at low doses. It is a single small study from more than forty years ago. When the European Food Safety Authority reviewed the research in 2011, it concluded that a cause-and-effect relationship between tryptophan and normal sleep had not been established (EFSA Panel on Dietetic Products, Nutrition and Allergies, 2011).
Tryptophan from food
Food-based studies give a mixed picture too.
- An evening serving of alpha-lactalbumin, a tryptophan-rich milk protein, raised the tryptophan ratio in blood by 130% and improved alertness the next morning (Markus et al., 2005).
- In 35 older adults, a week of tryptophan-enriched cereal at breakfast and dinner improved sleep efficiency and sleep time measured by wrist monitor (Bravo et al., 2013). The study was not randomised.
- In athletes with sleep difficulties, alpha-lactalbumin before bed for a week did not improve sleep (Barnard et al., 2025).
- In people with chronic insomnia, tryptophan from a protein source and pharmaceutical tryptophan both improved some insomnia measures over three weeks (Hudson et al., 2005), although the European review read this trial's main analysis as showing no effect (EFSA Panel on Dietetic Products, Nutrition and Allergies, 2011).
In a survey of nearly 30,000 American adults, higher tryptophan intake was linked with slightly longer sleep (Lieberman, Agarwal and Fulgoni, 2016).
Why UK supplements contain 220mg or less
If the research used a gram or more, why do UK supplements contain around 200mg? The answer is a piece of history.
In 1989 an outbreak of a serious illness, eosinophilia-myalgia syndrome, was linked to tryptophan supplements. More than 1,500 cases and at least 37 deaths were reported in the United States (Committee on Toxicity, 2004). Investigators traced it to product from a single manufacturer that had changed its production process, and identified a contaminant in the affected batches (Belongia et al., 1990). The cause was the contamination, not tryptophan itself (Fernstrom, 2012).
The UK banned tryptophan in foods in 1990. In 2004 the government's Committee on Toxicity reviewed the evidence and concluded that 220mg a day as a dietary supplement would not present an appreciable risk to health, provided the tryptophan meets European Pharmacopoeia purity standards (Committee on Toxicity, 2004). Regulations followed that allow tryptophan in food supplements up to a recommended daily dose of 220mg (Tryptophan in Food (England) Regulations 2005).
The 220mg figure is a safety margin, set by applying a tenfold caution factor to doses used in medicine. It was never intended as the dose that works best.
How OFFLINE Sleep uses tryptophan
OFFLINE Sleep contains 200mg of L-tryptophan, within the UK limit. At that level it adds roughly a quarter to a typical day's intake from food.
We are open about what that means. The trials showing a clear sleep benefit used five times as much or more. At 200mg, tryptophan is a supporting ingredient that supplies building blocks for your body's own serotonin and melatonin, alongside four other ingredients, and not a stand-alone sleep treatment. It is taken 30 to 45 minutes before bed, away from the protein of an evening meal.
Safety and who should avoid it
At dietary levels tryptophan is safe: even people with the highest intakes show no abnormal liver or kidney markers (Lieberman, Agarwal and Fulgoni, 2016). Side effects such as nausea, dizziness and tremor have been reported mainly at very high doses, many times the amount in UK supplements (Fernstrom, 2012).
The important caution is medication. In rare cases tryptophan combined with drugs that raise serotonin has caused serotonin syndrome, a potentially serious reaction (Fernstrom, 2012). Do not take tryptophan with antidepressants or other serotonin-acting medicines without speaking to your doctor or pharmacist.
Also check first if you are pregnant, breastfeeding or have a medical condition.
Frequently asked questions
Is tryptophan the same as melatonin? No. Tryptophan is the raw material your body uses to make serotonin and, from that, melatonin.
Is tryptophan the same as 5-HTP? No. 5-HTP is the next step along the pathway, after the rate-limiting conversion (Richard et al., 2009).
Does turkey make you sleepy? Probably not because of its tryptophan. Protein-rich meals supply competing amino acids, so they do not raise brain tryptophan the way people assume (Fernstrom and Wurtman, 1972; Wurtman et al., 2003).
Is tryptophan legal in the UK? Yes, in food supplements with a recommended daily dose of up to 220mg (Tryptophan in Food (England) Regulations 2005).
Will 200mg help me sleep? On its own, the evidence is limited to one small study showing a non-significant trend (Hartmann and Spinweber, 1979). That is why we use it as part of a formula and not as the headline ingredient.
The bottom line
Tryptophan has a sound biological rationale and a body of older research showing that gram-level doses can help people fall asleep. UK supplements are limited to 220mg a day for historical safety reasons, and at that level the direct evidence is slim. It earns a place in a combined formula as a precursor, and it should not be taken alongside antidepressants without medical advice.
This article is for general information and is not medical advice. Food supplements are not a substitute for a varied diet. If you have ongoing sleep problems, speak to your GP.
References
Barnard, J., Roberts, S., Lastella, M., Aisbett, B. and Condo, D. (2025) 'Pre-sleep alpha-lactalbumin supplementation does not improve the habitual sleep and performance of sportspeople with sleep difficulties', Nutrients, 17(7), 1196. doi:10.3390/nu17071196.
Belongia, E.A., Hedberg, C.W., Gleich, G.J., White, K.E., Mayeno, A.N., Loegering, D.A., Dunnette, S.L., Pirie, P.L., MacDonald, K.L. and Osterholm, M.T. (1990) 'An investigation of the cause of the eosinophilia-myalgia syndrome associated with tryptophan use', New England Journal of Medicine, 323(6), pp. 357–365. doi:10.1056/NEJM199008093230601.
Bravo, R., Matito, S., Cubero, J., Paredes, S.D., Franco, L., Rivero, M., Rodríguez, A.B. and Barriga, C. (2013) 'Tryptophan-enriched cereal intake improves nocturnal sleep, melatonin, serotonin, and total antioxidant capacity levels and mood in elderly humans', Age, 35(4), pp. 1277–1285. doi:10.1007/s11357-012-9419-5.
Brown, C.C., Horrom, N.J. and Wagman, A.M. (1979) 'Effects of L-tryptophan on sleep onset insomniacs', Waking and Sleeping, 3(2), pp. 101–108.
Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (2004) COT statement on tryptophan and the eosinophilia-myalgia syndrome. COT Statement 2004/01. Available at: https://webarchive.nationalarchives.gov.uk/ukgwa/20200803134320/https://cot.food.gov.uk/sites/default/files/cot/tryptophanamend200401.pdf (Accessed: 13 October 2026).
EFSA Panel on Dietetic Products, Nutrition and Allergies (2011) 'Scientific opinion on the substantiation of health claims related to L-tryptophan and maintenance of normal sleep (ID 596, 1671), enhancement of mood (ID 596), contribution to normal cognitive function (ID 596), and contribution to the maintenance or achievement of a normal body weight (ID 604) pursuant to Article 13(1) of Regulation (EC) No 1924/2006', EFSA Journal, 9(4), 2073. doi:10.2903/j.efsa.2011.2073.
Fernstrom, J.D. (2012) 'Effects and side effects associated with the non-nutritional use of tryptophan by humans', Journal of Nutrition, 142(12), pp. 2236S–2244S. doi:10.3945/jn.111.157065.
Fernstrom, J.D. and Wurtman, R.J. (1972) 'Brain serotonin content: physiological regulation by plasma neutral amino acids', Science, 178(4059), pp. 414–416. doi:10.1126/science.178.4059.414.
Hartmann, E. (1982) 'Effects of L-tryptophan on sleepiness and on sleep', Journal of Psychiatric Research, 17(2), pp. 107–113. doi:10.1016/0022-3956(82)90012-7.
Hartmann, E. and Spinweber, C.L. (1979) 'Sleep induced by L-tryptophan: effect of dosages within the normal dietary intake', Journal of Nervous and Mental Disease, 167(8), pp. 497–499. doi:10.1097/00005053-197908000-00008.
Hartmann, E., Lindsley, J.G. and Spinweber, C. (1983) 'Chronic insomnia: effects of tryptophan, flurazepam, secobarbital, and placebo', Psychopharmacology, 80(2), pp. 138–142. doi:10.1007/BF00427957.
Hudson, C., Hudson, S.P., Hecht, T. and MacKenzie, J. (2005) 'Protein source tryptophan versus pharmaceutical grade tryptophan as an efficacious treatment for chronic insomnia', Nutritional Neuroscience, 8(2), pp. 121–127. doi:10.1080/10284150500069561.
Lieberman, H.R., Agarwal, S. and Fulgoni, V.L. (2016) 'Tryptophan intake in the US adult population is not related to liver or kidney function but is associated with depression and sleep outcomes', Journal of Nutrition, 146(12), pp. 2609S–2615S. doi:10.3945/jn.115.226969.
Markus, C.R., Jonkman, L.M., Lammers, J.H.C.M., Deutz, N.E.P., Messer, M.H. and Rigtering, N. (2005) 'Evening intake of alpha-lactalbumin increases plasma tryptophan availability and improves morning alertness and brain measures of attention', American Journal of Clinical Nutrition, 81(5), pp. 1026–1033. doi:10.1093/ajcn/81.5.1026.
Richard, D.M., Dawes, M.A., Mathias, C.W., Acheson, A., Hill-Kapturczak, N. and Dougherty, D.M. (2009) 'L-tryptophan: basic metabolic functions, behavioral research and therapeutic indications', International Journal of Tryptophan Research, 2, pp. 45–60. doi:10.4137/IJTR.S2129.
Schneider-Helmert, D. and Spinweber, C.L. (1986) 'Evaluation of L-tryptophan for treatment of insomnia: a review', Psychopharmacology, 89(1), pp. 1–7. doi:10.1007/BF00175180.
Sutanto, C.N., Loh, W.W. and Kim, J.E. (2022) 'The impact of tryptophan supplementation on sleep quality: a systematic review, meta-analysis, and meta-regression', Nutrition Reviews, 80(2), pp. 306–316. doi:10.1093/nutrit/nuab027.
Tryptophan in Food (England) Regulations 2005 (SI 2005/2630). Available at: https://www.legislation.gov.uk/uksi/2005/2630/made (Accessed: 13 October 2026).
Wurtman, R.J., Wurtman, J.J., Regan, M.M., McDermott, J.M., Tsay, R.H. and Breu, J.J. (2003) 'Effects of normal meals rich in carbohydrates or proteins on plasma tryptophan and tyrosine ratios', American Journal of Clinical Nutrition, 77(1), pp. 128–132. doi:10.1093/ajcn/77.1.128.