Supplement analysis backed by scientific evidence · PT

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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.

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.

Scientific references

Where to buy

Douglas Laboratories, L-Tryptophan, 60 Vegetarian Capsules

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