5-Hydroxytryptophan (5-HTP)

We evaluated 40 human studies on 5-Hydroxytryptophan (5-HTP), including 17 randomised controlled trials and 4 meta-analyses or systematic reviews; the controlled studies include 539 participants in total. As of 14 October 2026.

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1. What Is 5-Hydroxytryptophan (5-HTP)? Occurrence, Origin and Forms

5-Hydroxytryptophan is an amino acid that the body makes from L-tryptophan and converts further into serotonin. As a supplement it is usually obtained from the seeds of the West African legume Griffonia simplicifolia. It is commonly used for low mood, for sleep problems and for complaints that are linked to serotonin metabolism.

In nature, 5-hydroxytryptophan occurs in the seeds of Griffonia simplicifolia and in small amounts in other plants and in animal tissues. In the body it is formed continuously as an intermediate step in the build-up of serotonin.

For supplements, 5-hydroxytryptophan is either extracted from Griffonia seeds or produced synthetically; as a medicinal substance it is called oxitriptan. Studies in humans mainly examine capsules and tablets containing 5-hydroxytryptophan alone, alongside combinations with carbidopa.

Forms and Preparations Studied

• 5-hydroxytryptophan as a pure substance in capsules or tablets
• Extract from the seeds of Griffonia simplicifolia
• Oxitriptan as a medicinal substance
• Preparations with delayed release
• Medicinal combination of oxitriptan and carbidopa
• Mixture products with further active substances

Not covered on this page:

• L-tryptophan, the precursor substance, is a substance in its own right with its own studies.
• Serotonergic drugs such as reuptake-inhibiting antidepressants are not 5-hydroxytryptophan preparations.
• Melatonin is a different substance with a different pathway.
• Carbidopa alone is not 5-hydroxytryptophan.

2. What Does 5-Hydroxytryptophan (5-HTP) Do? Results by Area

How to read the table: counted are human studies whose results concern the area. “High” means at least one meta-analysis and two controlled studies showing improvement, or at least three controlled studies of which three quarters show improvement, with at least 300 participants in total. “Moderate” means at least two controlled studies showing improvement, as a majority, or one meta-analysis alongside controlled studies. “Low” means one controlled study showing improvement. Where an area has no controlled study, the strength of evidence is at most “low” (result “reviews only” or “observational data only”). Everything else is “unclear”. A study counts as showing improvement when at least half of its outcomes in this area improved. Reviews of combination products do not count as meta-analyses; results that only describe side effects or shares of users do not count as an effect. The same study is counted only once.

3. What the Studies Show in Detail

5-Hydroxytryptophan (5-HTP) and Depressed Mood: Human Studies

In first depressive episode, depression scores decreased under 5-Hydroxytryptophan as a pure substance 7; in a preliminary study in Parkinson's patients, the Hamilton score fell more under the pure substance than under placebo 11. In a randomized controlled study, the response rate under the pure substance was not better than under fluoxetine 7. The robust findings predominantly concern the pure substance in capsules or tablets. Combination products with other active substances such as L-tryptophan, omega-3, SAMe, zinc, tyrosine, lecithin, L-glutamine, chlorimipramine or benzerazide say nothing about 5-Hydroxytryptophan alone 1210. The studies are mostly small and short, some without placebo comparison, and controlled data on delayed release as well as on Griffonia extract are lacking. It remains open whether the results can be transferred to other preparations and to longer-term use.

Further studies in this area: 34 36 37 38 40

5-Hydroxytryptophan (5-HTP) and Sleep: Human Studies

In older adults with poor sleep, 5-hydroxytryptophan as a pure substance shortened objective sleep onset latency compared with no intake, but subjective total sleep time decreased 12. In Parkinson's patients with REM sleep behavior disorder, the proportion of REM sleep increased, and the reported frequency of the disorder also improved under placebo 14. The strength of evidence is moderate; the controlled studies are small and short, and the forms investigated range from pure substance to combination products to oxitriptan, so findings cannot be transferred to other preparations.

Further studies in this area: 36 40

5-Hydroxytryptophan (5-HTP) and Fibromyalgia: Human Studies

In fibromyalgia, 5-hydroxytryptophan as a pure substance improved the clinical parameters in a controlled study with 50 participants 22. In a randomized comparative study, the combination of 5-hydroxytryptophan with an MAO inhibitor clearly improved the pain score, while the other treatments, including 5-hydroxytryptophan alone, brought lesser improvements 20. The evidence is weak: there is one controlled study on the pure substance; the second tested a combination product without a placebo arm. In addition, there is a case series, an observational study (case-control study) and a review 2440. 5-Hydroxytryptophan as a pure substance was investigated; results on Griffonia extract, oxitriptan or delayed-release preparations are lacking for this area.

5-Hydroxytryptophan (5-HTP) and Anxiety: Human Studies

For anxiety in older people, a small randomized study without placebo found no effect of 5-hydroxytryptophan as a pure substance on the anxiety score 8. A randomized controlled study on a combination product of 5-HTP with tyrosine, lecithin and L-glutamine reports an improvement in tension-anxiety, but this result applies only to the combination and not to 5-hydroxytryptophan alone 6. The evidence is unclear: for the pure substance there is only a small study with 30 participants without placebo, no meta-analysis. Capsules with 5-HTP pure substance as well as the aforementioned combination product were investigated; it remains open whether 5-hydroxytryptophan alone has any effect on anxiety at all.

5-Hydroxytryptophan (5-HTP), Appetite and Body Weight: Human Studies

For appetite and body weight, a meta-analysis that evaluated tryptophan and 5-hydroxytryptophan together found no difference in BMI compared with control groups 3; for 5-hydroxytryptophan alone, this cannot be inferred. A fat spread with 5-hydroxytryptophan, L-theanine, and γ-aminobutyric acid did not influence hunger and satiety according to the authors 18. A single case report on oxitriptan in a man with sepiapterin reductase deficiency reports an improvement in hyperphagia, but as a single case it cannot be generalized 28. A review that includes animal studies and clinical studies classifies the role of 5-hydroxytryptophan in obesity as unclear 36. The evidence is therefore overall unclear, and reliable statements on pure substance or Griffonia extract for appetite and weight are lacking.

5-Hydroxytryptophan (5-HTP): Further Outcomes in Studies

For this area, there are seven controlled studies with a total of 129 participants that tested 5-hydroxytryptophan in very different forms and in very different groups of people. Two small, single-blind studies with older adults and without placebo found a higher MoCA score and higher serum serotonin with the pure substance 8 as well as a more favorable microbiota composition in poor sleepers 9. The authors of the first study urge cautious interpretation because of the small sample. A randomized controlled study with a Griffonia simplicifolia extract showed no pain relief and even a greater extent of mechanical allodynia 13. The evidence is weak: the studies are predominantly small, short and investigate different forms, doses and populations, so the results are not generalizable.

Further studies in this area: 23 24 26 27 28 29 30 31 33 34 36

4. How Is 5-Hydroxytryptophan (5-HTP) Dosed? Preparation, Dose and Duration in Studies

The studies used 5-Hydroxytryptophan predominantly as a pure substance in capsules or tablets 789111214161722. Delayed-release preparations and oxitriptan as a drug were not tested in the controlled studies on the areas mentioned.

5. Is 5-Hydroxytryptophan (5-HTP) Safe? Side Effects in Studies

The reported side effects were predominantly mild and temporary 1322; fatigue, nausea or vomiting were also reported 17 as well as, without assignment to a treatment group, mild stomach pain and sleep disturbances 20. In an open case series, just under a third of the participants reported side effects, and one was therefore withdrawn from treatment 24.

6. What Remains Open: Limits of the Evidence

• The controlled studies are mostly small and short; many include only a few participants 8912131416.
• For Griffonia extract, oxitriptan and delayed-release preparations, controlled data are lacking for most areas.
• Results on combination products with other active substances cannot be transferred to 5-Hydroxytryptophan alone 123561015181920.
• The transferability to longer-term use and to other populations is open.
• For anxiety and for appetite and body weight, the evidence is limited or unclear.

7. Bottom Line: What Is Established About 5-Hydroxytryptophan (5-HTP)

5-Hydroxytryptophan is an amino acid and a precursor of serotonin. Controlled human research shows decreasing depression scores under the pure substance for depressive mood 7 and, preliminarily, in Parkinson's patients compared with placebo 11.

The strength of the evidence is limited by small and short studies, missing controlled data on Griffonia extract, oxitriptan and delayed release, as well as by the frequent testing of combination products. The reported side effects were predominantly mild and temporary 13172022.