Does Tryptophan Help You Sleep? Foods, Dose and the UK Limit

Tryptophan has trial evidence for one sleep measure: across the four trials a 2022 pooled analysis could combine, it shortened time awake after falling asleep, and people given 1 g or more a day spent 28.9 minutes awake against 56.6 minutes on under 1 g; other sleep measures did not change.¹ Two facts about dose sit beside that result: in England a food supplement may contain added L-tryptophan only if "the recommended daily dose for that food supplement does not exceed 220 mg", and higher amounts reach a person only through a pharmacist or hospital against a doctor's certificate.² Tryptophan is also the raw material for serotonin, so anyone on an antidepressant asks a pharmacist before adding it. The page sits under the Wellgard sleep guide.

Sources checked on 30 October 2026.

What is tryptophan, and how does it reach the brain?

Tryptophan is an essential amino acid: the body cannot make it, so it comes from protein in food. It is the scarcest amino acid in the body and the sole precursor of serotonin, which the brain then uses to make melatonin. A 2009 review puts the adult requirement at 250 to 425 mg a day and typical intake at 900 to 1,000 mg.³ Getting into the brain is the bottleneck: tryptophan crosses the blood-brain barrier on a transporter shared with five more abundant large neutral amino acids (valine, leucine, isoleucine, tyrosine and phenylalanine), so its ratio to those competitors matters as much as the amount. A carbohydrate-rich meal raises the ratio, because insulin lowers the competitors' blood levels, while a protein meal lowers it, because protein brings more of the competitors than tryptophan.³

Did tryptophan improve sleep in trials?

The 2022 review screened 18 articles and could pool four. Tryptophan shortened wake after sleep onset (standardised mean difference -1.08, 95% CI -1.89 to -0.28), and the dose split was the clearest finding: 28.9 minutes awake at 1 g or more against 56.6 minutes under 1 g (P = 0.001). It "did not affect other sleep components".¹ The 2009 review cites a 1979 study of deeper, stage 4 sleep at doses as low as 250 mg and shorter sleep latency from 1 g.³

The one modern trial near supplement doses added 175 mg of tryptophan to ashwagandha milk for 90 days in 52 adults with sleep problems: all three ashwagandha arms beat plain milk on a sleep-quality scale (P = 0.014), the tryptophan added nothing, and Pittsburgh index differences between groups were not significant.⁵

Why is tryptophan capped at 220 mg in a UK food supplement?

Because of rules first made in 1990, after the contamination episode described below, and remade in 2005. The Tryptophan in Food (England) Regulations 2005 (SI 2005/2630), in force since 11 November 2005, prohibit adding tryptophan to food, then list exceptions in regulation 5. Under 5(3), "Regulation 4 shall not apply in respect of laevorotatory tryptophan added to any food supplement if (a) the laevorotatory tryptophan complies with the purity criteria specified for that substance in the European Pharmacopoeia; and (b) the recommended daily dose for that food supplement does not exceed 220 mg." Under 5(1), more may be sold only "by a pharmacist" or by a hospital to a person with "an appropriate medical certificate". Scotland, Wales and Northern Ireland made matching regulations in 2005 with the same 220 mg limit.²

Tryptophan carries no authorised health claim in Great Britain: the sleep and "nervous balance" wordings submitted for it were assessed and not authorised (register entries 596 and 1671).⁶ The rest of the label is covered in how to choose a melatonin-free sleep supplement.

Which foods are highest in tryptophan, and does turkey make you sleepy?

Protein foods carry most of it. By the UK food tables, which give tryptophan divided by 60, a 30 g piece of Cheddar has about 120 mg, 40 g of porridge oats about 65 mg, a 30 g handful of pumpkin seeds about 130 mg, two slices of wholemeal bread about 100 mg and a 100 g banana about 12 mg.¹³ The review treats the ratio to the five competing amino acids as the better guide to brain uptake; CoFID does not list those amino acids, so the ratios below are the review's, from US food tables, and they run from 0.040 to 0.081:

Turkey's ratio (0.043) is no higher than chicken's (0.046) and lower than bread's or oats'. Drowsiness after a roast dinner has not been traced to the turkey; the carbohydrate on the plate raises the ratio for every protein eaten with it.^3,4 Foods that help you sleep builds these into an evening meal in UK portions.

Can you take tryptophan with antidepressants?

Ask the pharmacist or prescriber first, and tell them exactly what is in the product. For sertraline the NHS says: "Before taking sertraline, tell your doctor if you're taking any other medicines, herbal remedies, vitamins or supplements", and "Do not use the herbal supplement St John's wort when taking sertraline". The citalopram page adds strong painkillers "such as tramadol and buprenorphine", the migraine medicine sumatriptan and MAOI antidepressants "such as moclobemide" to the list that "may not mix well".^7,8 Tryptophan belongs in that conversation because SSRIs raise serotonin, tryptophan is its only precursor, and serotonin syndrome, in a 2023 review, "can occur through therapeutic use or overdose of a single serotonergic drug or as a drug interaction between two or more serotonergic drugs".^3,9 The NHS describes it as "a rare but serious condition that causes a fast heartbeat, sweating, shaking, twitching muscles and feeling confused or agitated", and says that if "you think you're having any other serious side effect, call NHS 111".⁷ The ingredient-by-ingredient table is in can you take sleep supplements with antidepressants.

What happened in 1989, and is tryptophan safe now?

In 1989 an epidemic of eosinophilia-myalgia syndrome (EMS), debilitating muscle pain with very high eosinophil counts, was recognised in the United States and linked to manufactured tryptophan: 1,531 cases and 27 deaths had been reported by 10 July 1990, and new cases fell sharply after over-the-counter products were recalled in November 1989.¹⁰ Analysis traced the products to a single producer and found more than 60 minor contaminants, six associated with the illness; a 2023 review concludes that "no clear and convincing conclusions have been drawn so far" about which was responsible.^10,11 The United States lifted its ban in 2001, and the 2005 Regulations admit only tryptophan meeting European Pharmacopoeia purity criteria.^2,3 No trial above reports on pregnancy or breastfeeding, so that question goes to a midwife, GP or pharmacist; months of poor sleep go to a GP (when to see a GP about sleep).

What we don't know

Whether 220 mg, the most a UK supplement may recommend, changes sleep: no trial has tested it alone, and 175 mg added to ashwagandha milk did no better than ashwagandha alone in 52 adults.⁵ Whether the night-waking result holds in larger trials, since it rests on four pooled studies.¹ Which contaminant caused the 1989 illness is still unsettled.¹¹

Frequently asked questions

Is 5-HTP the same as tryptophan?

No. The body makes 5-hydroxytryptophan from tryptophan through the rate-limiting enzyme tryptophan hydroxylase, and 5-HTP becomes serotonin wherever the decarboxylase enzyme is present; the 2006 review of 5-HTP centres its safety discussion on the same two concerns, eosinophilia myalgia syndrome and serotonin syndrome.¹² The 2005 Regulations define "tryptophan" as its laevorotatory, dextrorotatory and racemic forms "or any salt or peptide prepared from any of those forms" and do not name 5-HTP, so the 220 mg cap does not apply to it while the serotonin question applies to both.²

Which is better for sleep, tryptophan or magnesium?

No trial has measured them against each other. Tryptophan's pooled result is less time awake after falling asleep at 1 g or more; magnesium has its own trials and authorised wording (magnesium contributes to a reduction of tiredness and fatigue and to normal functioning of the nervous system), which tryptophan does not have.^1,6 Does magnesium help you sleep has the magnesium trials.

Which vitamin converts tryptophan to serotonin?

Vitamin B6 is a cofactor on the route; the 2009 review lists B6 or magnesium deficiency among the influences on serotonin synthesis, but says the tryptophan-to-competitor ratio and tryptophan availability are the two factors most likely to change it.³

Who should not take tryptophan without advice?

Anyone taking an antidepressant, a strong painkiller such as tramadol, a triptan or St John's wort, until a pharmacist or prescriber has checked it; anyone who has had eosinophilia-myalgia syndrome; and anyone pregnant or breastfeeding, for whom there is no trial evidence. Keep to the daily dose on the label.^7,8,10

Sources

1. Sutanto CN, Loh WW, Kim JE. The impact of tryptophan supplementation on sleep quality: a systematic review, meta-analysis, and meta-regression. Nutrition Reviews, 2022. Systematic review, 18 articles, 4 pooled; funding not stated on PubMed. PubMed 33942088
2. The Tryptophan in Food (England) Regulations 2005, SI 2005/2630, regulations 2, 4 and 5, and the matching 2005 Scotland, Wales and Northern Ireland regulations. legislation.gov.uk
3. Richard DM, et al. L-Tryptophan: basic metabolic functions, behavioral research and therapeutic indications. International Journal of Tryptophan Research, 2009. Narrative review; US government-funded. PubMed 20651948
4. Binks H, et al. Effects of diet on sleep: a narrative review. Nutrients, 2020. Narrative review; no conflicts declared. PubMed 32230944
5. Pérez-Piñero S, et al. Effectiveness of enriched milk with ashwagandha extract and tryptophan for improving subjective sleep quality in adults with sleep problems: a randomized double-blind controlled trial. Clocks & Sleep, 2024. Randomised double-blind trial, 52 adults, 90 days; no external funding, two authors from the dairy firm that made the milk. PubMed 39189195
6. Great Britain nutrition and health claims (NHC) register, 19 May 2026. gov.uk
7. NHS. Sertraline: taking sertraline with other medicines and herbal supplements; side effects of sertraline. Page last reviewed 8 September 2025. nhs.uk/medicines/sertraline
8. NHS. Citalopram: taking citalopram with other medicines and herbal supplements. Page last reviewed 26 June 2026. nhs.uk/medicines/citalopram
9. Mikkelsen N, Damkier P, Pedersen SA. Serotonin syndrome: a focused review. Basic & Clinical Pharmacology & Toxicology, 2023. Narrative review; funding not stated on PubMed. PubMed 37309284
10. Swygert LA, et al. Eosinophilia-myalgia syndrome: results of national surveillance. JAMA, 1990. National surveillance, 1,531 cases; US government (CDC). PubMed 2398610; Hill RH, et al. Contaminants in L-tryptophan associated with eosinophilia myalgia syndrome. Archives of Environmental Contamination and Toxicology, 1993. Laboratory analysis of case-linked lots; US government (CDC). PubMed 8346973
11. Ko SM, et al. Safety concerns regarding impurities in L-tryptophan associated with eosinophilia myalgia syndrome. Food and Chemical Toxicology, 2023. Narrative review; four authors employed by an amino-acid manufacturer. PubMed 37453474
12. Turner EH, Loftis JM, Blackwell AD. Serotonin a la carte: supplementation with the serotonin precursor 5-hydroxytryptophan. Pharmacology & Therapeutics, 2006. Narrative review; funding not stated on PubMed. PubMed 16023217
13. Public Health England. Composition of Foods Integrated Dataset (CoFID), 2021, vitamins table (tryptophan/60). Government food composition tables. gov.uk

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