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.

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 more than the amount. A carbohydrate-rich meal raises the ratio, because insulin clears the competitors into muscle; a purified dose taken away from protein raises it further, which is why the trials used isolated tryptophan and why tryptophan in food is not interchangeable with it.^3,4

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 used tryptophan as an add-on: 52 adults with sleep problems drank milk for 90 days with ashwagandha alone, ashwagandha plus 175 mg of tryptophan, a higher ashwagandha dose, or plain milk. All three ashwagandha arms beat the control on a sleep-quality scale (P = 0.014), but adding tryptophan did not add to ashwagandha alone, and between-group differences on the Pittsburgh index were not significant.⁵ Nobody has run a sleep-lab trial of 220 mg on its own; that is a gap, not a result.

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

Because of a 2005 law written after the contamination episode described below. 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".²

Both numbers are facts: 220 mg is the most a supplement label may recommend per day, and 1 g is where the pooled trials found their effect on night waking. The gap is a line the law has drawn, not a verdict on either side of it. Tryptophan also 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 tryptophan in proportion to their protein. In the 2009 review's table a 28 g piece of Cheddar has about 91 mg, a cup of oats 147 mg, 28 g of peanuts 65 mg, a slice of bread about 20 mg and a banana 11 mg.³ But the figure that decides brain uptake is the ratio to the five competing amino acids, and across foods it barely moves:

Turkey's ratio (0.043) is no higher than chicken's (0.046) and lower than bread's or oats'. The drowsiness after a roast dinner is better explained by the size of the meal and the carbohydrate on the plate, which raises the ratio for every protein eaten with it, than by anything particular to the bird.^3,4 Foods that help you sleep builds these into an evening meal in UK portions; does glycine help you sleep covers the other amino acid with sleep trials.

Can you take tryptophan with antidepressants?

Ask the pharmacist or prescriber first, and tell them exactly what is in the product. NHS medicine pages do not name tryptophan, but they set the rule; for sertraline: "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 None of the trials above reports on pregnancy or breastfeeding, so that question goes to a midwife, GP or pharmacist; sleep that has been poor for months is a GP matter whatever the supplement, as when to see a GP about sleep sets out.

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 sleep supplements have evidence behind them grades every ingredient on one scale.

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

What depletes tryptophan?

Dietary shortfall is unusual: typical intake is around 900 to 1,000 mg a day against a requirement of 250 to 425 mg.³ The "tryptophan depletion" people read about is a research technique, an amino-acid drink with the tryptophan left out, used to study serotonin's part in mood and sleep.^3,4

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. PubMed 33942088
2. The Tryptophan in Food (England) Regulations 2005, SI 2005/2630, regulations 2, 4 and 5. legislation.gov.uk
3. Richard DM, et al. L-Tryptophan: basic metabolic functions, behavioral research and therapeutic indications. International Journal of Tryptophan Research, 2009. PubMed 20651948
4. Binks H, et al. Effects of diet on sleep: a narrative review. Nutrients, 2020. 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. 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. nhs.uk/medicines/sertraline
8. NHS. Citalopram: taking citalopram with other medicines and herbal supplements. nhs.uk/medicines/citalopram
9. Mikkelsen N, Damkier P, Pedersen SA. Serotonin syndrome: a focused review. Basic & Clinical Pharmacology & Toxicology, 2023. PubMed 37309284
10. Swygert LA, et al. Eosinophilia-myalgia syndrome: results of national surveillance. JAMA, 1990. PubMed 2398610; Hill RH, et al. Contaminants in L-tryptophan associated with eosinophilia myalgia syndrome. Archives of Environmental Contamination and Toxicology, 1993. PubMed 8346973
11. Ko SM, et al. Safety concerns regarding impurities in L-tryptophan associated with eosinophilia myalgia syndrome. Food and Chemical Toxicology, 2023. PubMed 37453474
12. Turner EH, Loftis JM, Blackwell AD. Serotonin a la carte: supplementation with the serotonin precursor 5-hydroxytryptophan. Pharmacology & Therapeutics, 2006. PubMed 16023217