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Moderate evidenceSleep & relaxation

L-Tryptophan

Tryptophan above 1 g before bed measurably reduces time spent awake during the night, but its use for depression rests on old, poor-quality trials, and its safety history includes a fatal contamination outbreak.

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What the science says

  • Reduces wakefulness during the night at doses above 1 g Moderate evidence

    A systematic review, meta-analysis and meta-regression of tryptophan sleep trials found supplementation significantly reduced wake-after-sleep-onset, with the meta-regression indicating doses above 1 g/day drive the effect. Improvements in total sleep time and sleep efficiency were smaller and less consistent.

  • Antidepressant evidence is old and low quality Limited evidence

    A Cochrane review screened 108 trials of tryptophan and 5-HTP for depression and found only 2 (n=64) of adequate quality; those suggested benefit over placebo but the reviewers concluded the evidence was insufficient to recommend either as a treatment. No large modern RCT has resolved the question.

  • Mechanism depends on carbohydrate and competing amino acids Moderate evidence

    Tryptophan crosses the blood-brain barrier via a transporter shared with other large neutral amino acids, so a protein-rich meal blunts uptake while carbohydrate enhances it. This is why supplemental timing (away from protein, with a small carbohydrate serving) matters more for tryptophan than for most amino acids.

Dosage & safety

Studied doseSleep trials most often used 1-4 g taken 30-60 minutes before bed; effects on night-time wakefulness were clearest above 1 g. Older psychiatric trials used up to 6 g/day in divided doses.
SafetyCommon effects are daytime drowsiness, nausea, dry mouth and headache. Serious risk: serotonin syndrome when combined with SSRIs, SNRIs, MAOIs, triptans, tramadol or lithium — do not stack with serotonergic drugs. In 1989 a contaminated batch from a single manufacturer caused an outbreak of eosinophilia-myalgia syndrome with thousands of cases and dozens of deaths, leading to a years-long US import ban; modern pharmaceutical-grade material is considered safe but this is a reason to buy third-party tested product only. Tryptophan remains a prescription-only medicine for depression in several countries including the UK. Avoid in pregnancy and in people with carcinoid tumours or significant liver or kidney disease.

How to take it

Timing30-60 minutes before bed for sleep.
With food?On an empty stomach or with a small carbohydrate snack — protein supplies competing amino acids that block its entry into the brain.
Worth knowingOnly buy pharmaceutical-grade, third-party tested material: the 1989 eosinophilia-myalgia outbreak was a manufacturing contamination problem, not a tryptophan problem.

Interactions

With medications

  • SSRIs, SNRIs, MAOIs, tricyclics, triptans, tramadol and lithium

    Adding a serotonin precursor to serotonergic drugs can precipitate serotonin syndrome, which is potentially life-threatening. do not combine

  • sedatives, benzodiazepines and antihistamines

    Additive daytime drowsiness and impairment. do not drive until you know how the combination affects you

With other supplements

  • 5-HTP and St John's wort

    All three raise serotonin, and stacking them multiplies the serotonin syndrome risk without adding benefit. use only one

  • SAM-e

    Additive serotonergic effect. do not combine without medical advice

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Does L-tryptophan help you sleep?

The evidence is moderate: a meta-analysis found L-tryptophan reduced time spent awake during the night, with the effect driven by doses above 1 g/day. Effects on total sleep time were smaller.

How should I take tryptophan for sleep?

Take 1–4 g of L-tryptophan 30–60 minutes before bed, on an empty stomach or with a small carbohydrate snack. Protein supplies competing amino acids that block tryptophan's entry into the brain.

Does L-tryptophan work for depression?

The evidence is limited: a Cochrane review found only 2 adequate-quality trials among 108 screened, and concluded the evidence is insufficient to recommend tryptophan as a treatment.

Is L-tryptophan safe with antidepressants?

No. Combining L-tryptophan with SSRIs, SNRIs, MAOIs, triptans, tramadol or lithium can cause serotonin syndrome, which is potentially life-threatening, so do not combine them.

Scientific references

Where to buy

Douglas Laboratories, L-Tryptophan, 60 Vegetarian Capsules

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