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L-Tryptophan

Serotonin · sleep · mood

Moderate evidenceVegan132 studies on PubMedRead the research
Written to our editorial standards · reviewed against published research· Updated 30 May 2026
Last reviewed: May 30, 2026

L-Tryptophan: Serotonin · sleep · mood. The amino acid precursor to serotonin and melatonin. Gentler than 5-HTP for sleep onset and mood support. Standard dose 1 g, taken in the evening, about $22/month. Evidence rating: moderate evidence.

Where to buy

NOW Foods L-Tryptophan 500mg
Recommended
NOW Foods, L-Tryptophan
1 g · Evening · ~$22/month

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NOW Foods L-Tryptophan 500mgBestseller
L-Tryptophan 500mg
NOW Foods
120 veg caps · $22 · ★ 4.7
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L-Tryptophan 500 mg
NOW Foods
120 veg caps · $18 · ★ 4.7
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What is L-Tryptophan?

L-Tryptophan is one of the nine essential amino acids and the precursor to both serotonin (the mood-regulating neurotransmitter) and melatonin (the sleep hormone). Unlike 5-HTP, which skips part of the regulatory pathway, tryptophan converts to serotonin under normal physiological control, making it gentler and better suited for long-term use. Clinical trials support tryptophan for sleep latency, mood, and PMS symptoms. It should not be combined with SSRIs or other serotonergic medications. Standard dose is 500 mg-2 g, taken in the evening on an empty stomach with a small carbohydrate.

The amino acid precursor to serotonin and melatonin. Gentler than 5-HTP for sleep onset and mood support.

Natural food sources

Where possible, get L-Tryptophan from whole foods first. Common dietary sources include:

Turkey & chickenEggsCheesePumpkin seedsOats

Best for your goal

Interactions

Other amino acids

L-Theanine (Suntheanine)
Calm focus · stress
Glycine
Sleep depth · core body temperature
N-Acetyl Cysteine (NAC)
Liver · antioxidant · respiratory
Taurine
Heart · sleep · cellular hydration

Common questions

What is L-Tryptophan?
L-Tryptophan is one of the nine essential amino acids and the precursor to both serotonin (the mood-regulating neurotransmitter) and melatonin (the sleep hormone). Unlike 5-HTP, which skips part of the regulatory pathway, tryptophan converts to serotonin under normal physiological control, making it gentler and better suited for long-term use. Clinical trials support tryptophan for sleep latency, mood, and PMS symptoms. It should not be combined with SSRIs or other serotonergic medications. Standard dose is 500 mg-2 g, taken in the evening on an empty stomach with a small carbohydrate.
What is L-Tryptophan used for?
Serotonin · sleep · mood. The amino acid precursor to serotonin and melatonin. Gentler than 5-HTP for sleep onset and mood support.
What is the standard dose of L-Tryptophan?
1 g, typically taken in the evening. Approximate cost is $22 per month.
Who should avoid L-Tryptophan?
Use extra caution, and speak to a clinician first, if you are bipolar disorder.
How strong is the evidence for L-Tryptophan?
Moderate evidence for its primary uses. See the full study list on the research page.

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