Amino Acid

5-HTP

5-Hydroxy-L-tryptophan

Evidence TierCWADA NOT PROHIBITED

tuneTypical Dose

100-300 mg/day in legacy adult reports

watchEffect Window

Possible changes by 2-4 weeks, clearer signal by 4-12 weeks in some studies.

check_circleCompliance

WADA NOT PROHIBITED

Overview

Clinical Summary

5-HTP is a serotonin precursor derived from tryptophan. It is used to support mood and sleep patterns and to influence appetite through serotonin availability.

Small trials suggest reduced depressive symptoms and improved sleep onset, with some evidence for fewer tension-type headaches or migraines. Some studies also report reduced appetite and carbohydrate cravings. Evidence is heterogeneous and often small, so effects appear most reliable in mild mood symptoms or stress-related insomnia.

Precursor to serotonin that may increase serotonergic tone. Clinical effect size and consistency remain uncertain across modern settings.

Outcomes

What This Is Expected To Influence

Primary Outcomes

  • Possible reduction in depressive symptom burden in some adult cohorts.
  • Limited adjunctive improvement signals in fibromyalgia-related pain/sleep endpoints.

Secondary Outcomes

  • Sleep latency or sleep quality changes (limited evidence).
  • Biological plausibility for serotonergic pathway modulation.

Safety

Contraindications and Interactions

Contraindications

  • Pregnancy or lactation
  • Serotonergic instability or prior serotonin-toxicity episodes
  • Bipolar disorder or unstable mood states
  • Active serotonergic medication regimens without clinician oversight
  • Severe hepatic or renal disease until medically reviewed

Side effects

  • Nausea - Taking 5-HTP 100 milligrams 2-3 times daily, rather than all at once, may prevent this side effect.
  • Vomiting - Taking 5-HTP 100 milligrams 2-3 times daily, rather than all at once, may prevent this side effect.
  • Constipation
  • Diarrhea
  • Headache - Less common
  • Insomnia - Less common
  • Palpitations - Less common
  • Dizziness
  • Drowsiness/sedation
  • Vivid dreams
  • Dose-dependent GI upset with larger single doses

Interactions

  • Carbidopa (Probable/Minor) - Carbidopa increases bioavailability/exposure of 5-HTP.
  • Serotonergic drugs including SSRIs, SNRIs, MAOIs, linezolid, tramadol, and triptans (Theoretical/Unknown) - Additive serotonergic effects can increase serotonin-toxicity risk.
  • Serotonergic supplements (Theoretical/Unknown) - Combining with other serotonergic supplements can increase additive serotonergic effects.

Avoid if

  • Pregnancy or lactation
  • People using carbidopa unless medically coordinated
  • Severe mood instability or active suicidality
  • Unstable endocrine or cardiovascular disease
  • Anticoagulation without medical oversight

Evidence

Study-level References

5-htp-SRC-001Systematic review + meta-analysis (mixed trial designs)
Sourceopen_in_new

Effects of 5-hydroxytryptophan on distinct types of depression: a systematic review and meta-analysis, PMID: 31504850, DOI: 10.1093/nutrit/nuz039.

Population: Adults with depression or depressive symptoms across heterogeneous study designs

Dose protocol: Oral 5-HTP protocols with variable dose ranges and comparators, generally evaluated over 4-12 weeks

Key findings: Directionally positive pooled signal, but high heterogeneity weakens confidence in exact effect size. Remission and symptom reduction were reported, but pooled certainty was limited by heterogeneity.

Notes: Older studies, varying quality, inconsistent diagnostic endpoints.

Paper content

Directionally positive pooled signal; high heterogeneity weakens confidence in exact effect size. Remission and symptom reduction were reported, but pooled certainty was limited by heterogeneity.

5-htp-SRC-002Systematic review
Sourceopen_in_new

Older pooled evidence review for depression, PMID: 12169147, DOI: 10.1002/14651858.CD003188.

Population: Adults with depressive syndromes in legacy controlled and comparative studies

Dose protocol: Non-standardized doses and short follow-up windows

Key findings: Directionally favorable in some studies, but effect reliability is low. Supports possibility of benefit but does not establish definitive clinical equivalence.

Notes: Methodologic limitations and incomplete trial comparability reduce confidence.

Paper content

Directionally favorable in some studies, but effect reliability is low. Supports possibility of benefit but does not establish definitive clinical equivalence.

5-htp-SRC-003Randomized, double-blind, placebo-controlled trial
Sourceopen_in_new

RCT in fibromyalgia with 5-HTP, PMID: 2193835.

Population: Adults with fibromyalgia-like pain syndromes (n=50 in report context)

Dose protocol: Controlled adjunctive oral 5-HTP protocol. Abstract-accessible dosage detail is limited

Key findings: Reported improvement across assessed symptom domains in directionally favorable direction. Suggestive benefit in short duration pain and associated symptom outcomes.

Notes: Modest sample and incomplete protocol granularity in accessible report.

Paper content

Reported improvement across assessed symptom domains in directionally favorable direction. Suggestive benefit in short duration pain and associated symptom outcomes.

5-htp-SRC-004Open-label clinical trial
Sourceopen_in_new

Open-label adjunctive experience in fibromyalgia and sleep-related complaints, PMID: 1521674.

Population: Adults with fibromyalgia-like symptoms

Dose protocol: ~90-day adjunctive protocol. Exact mg per day not fully standardized in summary

Key findings: ~50% symptom improvement reported, but tolerability limited by ~30% adverse effects and attrition. Weak-to-moderate supportive signal with high uncertainty.

Notes: Non-blinded design and protocol-era reporting limit causal interpretation.

Paper content

~50% symptom improvement reported; tolerability limited by ~30% adverse effects and attrition. Weak-to-moderate supportive signal; high uncertainty.

5-htp-SRC-005Randomized crossover pharmacodynamic study
Sourceopen_in_new

Pharmacologic interaction trial in healthy participants, PMID: 11910264.

Population: Healthy volunteers

Dose protocol: 100 mg and 200 mg oral conditions with/without carbidopa interaction arm

Key findings: Demonstrates dose-response and endocrine/biological effects, but not efficacy proof for clinical syndromes. Supports biological plausibility and cautions around serotonergic interactions.

Notes: Healthy volunteer sample and limited external validity.

Paper content

Demonstrates dose-response and endocrine/biological effects; not efficacy proof for clinical syndromes. Supports biological plausibility and cautions around serotonergic interactions.

5-htp-SRC-006Narrative review
Sourceopen_in_new

Safety and mechanism review, PMID: 9727088, DOI: 10.1016/j.nurt.2005.05.006.

Population: Preclinical, pharmacologic, and mixed clinical data synthesis

Dose protocol: Multi-source protocol synthesis

Key findings: Mechanistic rationale supportive, but clinical signal remains non-definitive. Supports mechanistic framing and safety-guardrails.

Notes: Older evidence base with variable reporting quality.

Paper content

Mechanistic rationale supportive; clinical signal remains non-definitive. Supports mechanistic framing and safety-guardrails.

5-htp-SRC-007Regulatory policy resource
Sourceopen_in_new

World Anti-Doping Agency, Prohibited List resources, official WADA governance pages (URL).

Population: Competitive sport governance

Dose protocol: Annual list updates, not dose-driven

Key findings: No efficacy inference, only compliance relevance. Requires annual verification and does not provide efficacy evidence.

Notes: Rules change each season. Status should be rechecked continuously.

Paper content

No efficacy inference; only compliance relevance. Requires annual verification and does not provide efficacy evidence.

5-htp-SRC-008Regulatory policy resource
Sourceopen_in_new

U.S. Dietary Supplement regulatory overview and DSHEA framework references (official government summary).

Population: Product oversight context (U.S. market)

Dose protocol: Not clinical protocol content. Category- and labeling-oriented

Key findings: No efficacy signal. Indicates classification/oversight implications only. Helps classify implementation and labeling expectations.

Notes: Policy interpretation differs by jurisdiction and enforcement timeline.

Paper content

No efficacy signal; indicates classification/oversight implications only. Helps classify implementation and labeling expectations.

5-htp-SRC-009Single-blinded randomized controlled trial.
Sourceopen_in_new

Li S, Sutanto CN, Xia X, Kim JE. The Impact of 5-Hydroxytryptophan Supplementation on Cognitive Function and Mood in Singapore Older Adults. Nutrients. 2025;17(17):2773. doi:10.3390/nu17172773. PMID:40944161.

Population: Community-dwelling older adults in Singapore.

Dose protocol: 100 mg/day oral 5-HTP for 12 weeks versus no-supplement control

Key findings: Significant improvement in MoCA cognitive scores, increased serum serotonin, and reduced Geriatric Depression Scale scores. No significant effect on anxiety measures.

Notes: Small sample (n=30), single-blind design, single-region cohort. Provides the first modern RCT signal for 5-HTP on cognition and mood in older adults.

Paper content

This 12-week single-blinded RCT in 30 Singaporean older adults found that 100 mg daily 5-HTP supplementation significantly improved Montreal Cognitive Assessment scores, increased serum serotonin levels, and reduced Geriatric Depression Scale scores compared to a no-supplement control. Anxiety measures were not significantly affected. The trial provides modern human evidence supporting 5-HTP's serotonergic activity and its potential for cognitive and mood support in older adults, though the small sample size and single-blind design limit generalizability.

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