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5-HTP (5-hydroxytryptophan)

Status: Dietary supplement
Evidence: Not graded on a research bench yet

5-HTP (5-hydroxytryptophan) is an amino acid that the body makes from tryptophan on the way to serotonin and melatonin, and the L form sold in supplements has been extracted commercially from the seeds of the West African plant Griffonia simplicifolia.

Reviewed 28 October 2026

01Overview

What 5-HTP (5-hydroxytryptophan) is

5-HTP is sold in the United States as a dietary supplement, and in Italy oxitriptan (L-5-HTP) is an authorized prescription medicine (PMID: 15068828, PMID: 28210931; Italian Medicines Agency database, checked 25 October 2026). Small trials have tested 5-HTP in depression, sleep terrors, appetite, fibromyalgia and headache, but a 2002 Cochrane review of 5-HTP and tryptophan found only two depression trials, with 64 patients, good enough to analyze (PMID: 11869656). 5-HTP has been studied for a possible link to eosinophilia-myalgia syndrome through contaminants, and for serotonin-related reactions when combined with other serotonergic drugs (PMID: 7699627, PMID: 12508395, PMID: 16023217).

How it works

Where 5-HTP sits in serotonin synthesis

The body makes 5-HTP from the amino acid tryptophan with the enzyme tryptophan hydroxylase (TPH), which exists in two forms, TPH1 and TPH2 (PMID: 33375373). Removing a carboxyl group from 5-HTP (decarboxylation) gives serotonin (5-hydroxytryptamine), and serotonin can be converted further to melatonin (PMID: 33375373). The tryptophan-to-5-HTP step is the rate-limiting step in serotonin and melatonin synthesis, and 5-HTP taken by mouth enters the pathway after that step (PMID: 33375373). The form in supplements and in the prescription drug oxitriptan is the L form, L-5-hydroxytryptophan (PMID: 33375373).

Read the full mechanismShow less

Conversion outside the brain

How much 5-HTP reaches the brain depends on how much is first converted to serotonin elsewhere in the body by the enzyme aromatic amino acid decarboxylase, and carbidopa, a peripheral decarboxylase inhibitor, blocks that conversion outside the brain (PMID: 16023217). In a crossover study of 12 healthy men, adding carbidopa to a 100 mg dose of 5-HTP doubled its elimination half-life and made total exposure (area under the curve) 15.4 times larger (PMID: 11910264). Studies in myoclonus and serotonin challenge tests have given 5-HTP together with carbidopa (PMID: 6966118, PMID: 18308795, PMID: 11910264).

What 5-HTP changes in people

Blood serotonin. In a 166-patient trial in inflammatory bowel disease, serum 5-HTP and serotonin rose during 5-HTP treatment compared with placebo (PMID: 35940251).
Stress hormones. 5-HTP is used as a challenge test of serotonin function: in 15 healthy men given 5-HTP with carbidopa, cortisol and prolactin rose with dose (PMID: 18308795).
Urine test for serotonin breakdown. In 8 healthy adults, 10 days of 5-HTP raised urinary 5-hydroxyindoleacetic acid (5-HIAA), which is commonly measured to detect carcinoid tumors, to a median of 204 micromol a day against 18 on placebo (PMID: 18209781).

Where 5-HTP comes from

Seeds of the West African plant Griffonia simplicifolia contain 6 to 20 percent 5-HTP by wet weight (PMID: 33991640). Commercial 5-HTP has been produced by extraction from these seeds (PMID: 24936877). Wild West African populations are the sole commercial source of the seed, China is the main importer, and about 48 percent of the re-exported 5-HTP extracts go to North America (PMID: 33991640).

Absorption and slow-release research

Researchers at Duke University have argued that ordinary 5-HTP is absorbed and eliminated too quickly to work well as a drug, and have tested slow-release forms in mice (PMID: 27692695, PMID: 26932820). In mice given an SSRI antidepressant, ordinary 5-HTP injections caused brief serotonin spikes and marked adverse effects, while slow-release 5-HTP raised extracellular brain serotonin beyond the SSRI effect with no adverse effect observed (PMID: 26932820). A 2026 review, written with an author from the company Evecxia Therapeutics, notes that 5-HTP has poor drug properties and that no FDA-approved drug uses this approach to add to antidepressants (PMID: 41928689).

Studied for

Depression
Serotonin biochemistry
Sleep
Appetite and obesity
Fibromyalgia
Headache
Cerebellar ataxia
Eosinophilia-myalgia syndrome

Benefits listed

Hamilton depression scores similar to fluoxetine in a 70-patient trial without placebo (PMID: 23380314)
Depression scores in a 25-patient Parkinson's disease crossover trial (PMID: 32067288)
Panic response to a carbon dioxide challenge in 24 panic disorder patients (PMID: 12559480)
Sleep terror episodes in an open trial in 45 children (PMID: 15146330)

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Food intake and body weight in small trials in obese adults (PMID: 2468734, PMID: 1384305)
Fibromyalgia symptom measures in a 50-patient placebo-controlled trial (PMID: 2193835)
Ataxia scores in a 30-patient cerebellar ataxia trial (PMID: 3190503)

02Research

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What the research shows

No research bench grades 5-HTP (5-hydroxytryptophan) yet. Benches compare compounds people pair, with the evidence for each.

Key research findings

Depression

Cochrane review, 2002. Of 108 trials of 5-HTP or tryptophan for depression, only 2, with 64 patients in total, were good enough to include. Together they suggested 5-HTP and tryptophan were better than placebo (Peto odds ratio 4.10), but the review judged the evidence of insufficient quality to be conclusive (PMID: 11869656).
Javelle 2020, meta-analysis of 13 studies. The pooled remission rate was 0.65 and the questionnaire effect size was large (Hedges' g 1.11), but heterogeneity was high and the authors rated the studies as relatively weak, noting that few had placebo groups (PMID: 31504850).
Jangid, India, 70 patients with a first depressive episode (60 completed), 8 weeks, double-blind. L-5-HTP and fluoxetine reduced HAM-D scores by similar amounts, and 73.3 percent on L-5-HTP and 80 percent on fluoxetine responded. There was no placebo arm (PMID: 23380314).
Nolen 1988, the Netherlands, treatment-resistant depression. Two partial crossover studies enrolled 47 patients who had failed at least two antidepressants: the first was an open comparison of the MAO inhibitor tranylcypromine with L-5-HTP, the second a double-blind comparison with nomifensine. Apart from one patient, neither the patients treated with L-5-HTP nor those treated with nomifensine improved, while tranylcypromine was effective in 50 percent of patients (PMID: 3146891).
Sarris and colleagues, Australia, 158 patients, 8 weeks. A combination product containing 5-HTP, SAM-e, folinic acid, omega-3 fatty acids, zinc and co-factors did no better than placebo (response 40 against 51 percent, non-significant), and the trial cannot separate the share of 5-HTP (PMID: 30699842).
Parkinson's disease, University of Cagliari, 25 patients, crossover with 4-week treatment periods. The same Cagliari group ran all three Parkinson's disease trials on this page (PMID: 32067288, PMID: 32464351, PMID: 34403081). 5-HTP at 50 mg a day improved depression scores on the Hamilton scale compared with placebo but did not change apathy (PMID: 32067288).
Older adults, National University of Singapore, 30 participants, 12 weeks, single-blind, no placebo. This one trial is reported in two papers (ClinicalTrials.gov NCT04078724), and cognition and mood were among its registered secondary outcomes. Montreal Cognitive Assessment scores rose from 26.6 to 27.6 within the group given 5-HTP at 100 mg a day; scores also rose in the untreated group, and the paper reports a change over time rather than a difference between the groups. Geriatric Depression Scale scores fell by week 8 within the 5-HTP group, and anxiety scores did not change (PMID: 40944161).

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Anxiety, panic and obsessive-compulsive disorder

Panic, Maastricht, 24 patients and 24 healthy volunteers. A single 200 mg dose of L-5-HTP reduced subjective anxiety, panic symptoms and panic attacks during a 35 percent carbon dioxide challenge in patients compared with placebo, with no effect in the volunteers (PMID: 12559480).
Obsessive-compulsive disorder, Tehran, 60 patients, 12 weeks. Adding 5-HTP at 100 mg twice a day to fluoxetine improved Y-BOCS scores and response rates more than adding placebo (PMID: 32541380).

Sleep

Sleep terrors, Rome, 45 children. In an open trial, 31 randomly selected children were given L-5-HTP at bedtime for 20 days and 14 were not treated. After 1 month, 93.5 percent of treated children had responded, against episodes disappearing in 28.6 percent of the comparison group, and 83.9 percent of treated children were free of sleep terrors at 6 months. There was no placebo (PMID: 15146330).
Older adults, National University of Singapore, the same 30-participant trial. On sleep quality, one of the trial's registered primary outcomes, 5-HTP at 100 mg a day improved some sleep measures, and the Pittsburgh Sleep Quality Index global score improved significantly only in participants who were poor sleepers at the start; serum serotonin rose (PMID: 38309227).
REM sleep behavior disorder in Parkinson's disease, Cagliari, 18 patients, crossover. 5-HTP increased the share of REM sleep without more episodes of the disorder; self-reported episode frequency improved on both 5-HTP and placebo (PMID: 34403081).

Appetite and weight

Ceci 1989, University of Rome La Sapienza, 19 obese women, 5-week crossover. Both obesity trials below come from this Rome group (PMID: 2468734, PMID: 1384305). 5-HTP reduced food intake and body weight and produced appetite-loss symptoms, with no change in mood (PMID: 2468734).
Cangiano 1992, Rome, 20 obese patients, two 6-week periods. 5-HTP at 900 mg a day was followed by weight loss in both periods, lower carbohydrate intake and early satiety (PMID: 1384305).
Exercise-trained adults, 48 randomized, 8 weeks. Fat mass measured by bioimpedance fell more with 5-HTP at 100 mg a day than with placebo (p=0.048), while lean mass and percent body fat did not change significantly (PMID: 35583055).

Pain and headache

Fibromyalgia, Milan, 50 patients, double-blind and placebo-controlled. All clinical measures studied improved significantly with 5-HTP, and only mild, transient side effects were reported (PMID: 2193835).
Migraine prevention, 124 patients. Improvement was seen in 71 percent on 5-HTP and 75 percent on methysergide; there was no placebo arm (PMID: 3536521).
Childhood migraine, 21 children, crossover against placebo. Migraine fell during both treatments, and 5-HTP did not differ from placebo in the first treatment period (PMID: 3533271).
Chronic tension-type headache, Portugal, 78 patients, 8 weeks. 5-HTP at 300 mg a day did not reduce headache days or intensity compared with placebo, although analgesic use fell (PMID: 10849040).

Neurology

Cerebellar ataxia, Lyon, 30 patients, 4 months. Pierre Trouillas's group in Lyon led both ataxia trials (PMID: 3190503, PMID: 7733839). L-5-HTP improved the ataxia score and timed tests of standing, walking, speech and writing compared with placebo (PMID: 3190503).
Friedreich's ataxia, 12 centers, 26 patients (19 completed). L-5-HTP improved a coordination score, which the authors called partial and not clinically major (PMID: 7733839).
Levodopa-induced dyskinesia in Parkinson's disease, Cagliari, 12 patients, crossover. 5-HTP at 50 mg a day improved dyskinesia rating scores compared with placebo (PMID: 32464351).
Tetrahydrobiopterin (BH4) deficiency. In this rare inherited disorder of serotonin and dopamine synthesis, replacement therapy with 5-HTP and L-dopa is the cornerstone of treatment (PMID: 25707872).

Trials that found no benefit

Fatigue in inflammatory bowel disease, 13 Belgian hospitals, 166 patients, 8-week crossover periods. 5-HTP at 100 mg twice a day did not meet the primary endpoint: 35.6 percent on 5-HTP and 37.6 percent on placebo had at least a 20 percent fall in fatigue scores, despite higher serum 5-HTP and serotonin (PMID: 35940251).
Menopausal hot flashes, 24 women. 5-HTP at 150 mg a day did not reduce hot flashes measured with an electronic recorder (PMID: 20031347).
Alcohol abstinence, National Institute on Alcohol Abuse and Alcoholism, 1 year. Neither 5-HTP with carbidopa nor levodopa with carbidopa improved abstinence compared with placebo among 31 analyzed patients (PMID: 1424429).
Adults with high or low ADHD traits, Sheffield, 112 participants (56 with high traits), single dose. 5-HTP did not improve any measure of distractibility (PMID: 42160304).

Human pharmacokinetics

Westenberg 1982, 5 healthy volunteers pretreated with carbidopa. The half-life ranged from 2.2 to 7.4 hours, and oral bioavailability with carbidopa was 48 percent (PMID: 6187038).
Magnussen 1979 and 1980, five patients in each study, with a decarboxylase inhibitor. After intravenous dosing in carbidopa-pretreated patients the half-life was about 6 hours (PMID: 311987), and in patients with myoclonic disorders oral bioavailability at steady state ranged from 47 to 84 percent, with peak levels 1.8 to 3.3 hours after a dose (PMID: 6966118).
Gijsman 2002, 12 healthy men. Carbidopa doubled the elimination half-life of 5-HTP and raised exposure 15.4 times (PMID: 11910264).

Animal studies

These are not human results: serotonin syndrome signs in mice given 5-HTP, fluoxetine or tranylcypromine, increased by combining them (PMID: 24780865), exaggerated responses in MAO knockout mice (PMID: 22964922), adverse effects of ordinary 5-HTP with an SSRI in mice and none observed with slow-release 5-HTP (PMID: 26932820), and serotonin syndrome-like poisoning in dogs (PMID: 10863592).

Safety and side effects

What the trials recorded

In kinetics and challenge studies, nausea and vomiting were the side effects reported most often, and they rose with dose and blood level (PMID: 18308795, PMID: 6187038). In 15 healthy men given 5-HTP with carbidopa, nausea and vomiting led 6.6 percent to drop out at 100 mg and 45.5 percent at 300 mg (PMID: 18308795). In a kinetics study, gastrointestinal side effects appeared to track the plasma 5-HTP concentration (PMID: 6187038), and intravenous infusions had to be stopped in four experiments because patients became nauseated and vomited (PMID: 311987). After a single dose in a 112-adult trial, 19.6 percent of the 5-HTP group reported fatigue, nausea or vomiting (PMID: 42160304).

Read all the safety notesShow less

Longer trials reported few or mild adverse events. In a 50-patient fibromyalgia trial only mild and transient side effects were reported (PMID: 2193835). In a 124-patient migraine trial, side effects were more frequent with methysergide than with 5-HTP (PMID: 3536521). In a 78-patient tension-type headache trial, treatment was stopped for adverse events in 4 patients on 5-HTP and 3 on placebo (PMID: 10849040). A 1987 review found relatively few adverse effects in depressed patients given 5-HTP (PMID: 3298325).

Eosinophilia-myalgia syndrome and contaminants

The tryptophan epidemic. In 1989 an epidemic of eosinophilia-myalgia syndrome (EMS), a disorder of debilitating muscle pain and high eosinophil counts, was linked to manufactured L-tryptophan, the amino acid one step before 5-HTP (PMID: 2398610). By 10 July 1990, 1,531 US cases had been reported, including 27 deaths, and new cases fell sharply after over-the-counter tryptophan was recalled in November 1989 (PMID: 2398610). By 10 August 1991, 36 EMS deaths had been reported to the CDC (PMID: 8295183). A Minnesota case-control study tied the cases to tryptophan from a single manufacturer and to specific manufacturing conditions (PMID: 2370887).
A 5-HTP family case. FDA and NIH researchers described a family who became ill after exposure to L-5-HTP: one member had EMS and two others had high eosinophil counts. The family's 5-HTP contained an impurity not found in other patients' supplies, and the eosinophil counts of two family members returned to normal after they switched to 5-HTP without that impurity (PMID: 7699627). In a second group of patients with extended 5-HTP exposure, whose samples lacked the impurity, none developed EMS but 2 developed high eosinophil counts (PMID: 7699627).
Peak X. Mayo Clinic chemists found a family of contaminants called peak X in all eight commercial 5-HTP samples they tested (PMID: 10721089), and later identified one of them, X1, as 4,5-tryptophan-dione, a suspected neurotoxin, in the case-implicated 5-HTP and in 6 over-the-counter samples, at 0.5 to 10.3 percent of the amount in the case-implicated sample (PMID: 12508395).
The opposing view. A 2004 review argued that no definitive case of 5-HTP toxicity had emerged in 20 years of worldwide use, except one unresolved case in a Canadian woman, and that the peak X reports lacked credibility because of chromatographic artifacts and tiny concentrations (PMID: 15068828).
Status of the question. The 2002 Cochrane review on 5-HTP and tryptophan for depression concluded that the possible link between these substances and EMS had not been explained (PMID: 11869656).

Other reported harms

Scleroderma-like illness. A scleroderma-like illness developed in a patient treated with L-5-HTP and carbidopa for intention myoclonus (PMID: 6997735).
Overdose. A 44-year-old man who accidentally took ten times the recommended amount of 5-HTP powder developed marked memory loss and confusion, with MRI changes in both hippocampi suggestive of ischemia or seizure, which the authors attributed to drug-induced ischemia; his memory recovered enough for him to return to work after two months, and the MRI was normal at 11 months (PMID: 35878559).
Mood switch. A 42-year-old man developed hypomania about a week after starting 5-HTP together with SAM-e for depression (PMID: 29955516).
False-positive cancer screening test. 5-HTP raised urinary 5-HIAA in healthy volunteers, and in a 77-year-old woman raised urinary 5-HIAA and chromogranin A both returned to normal after she stopped 5-HTP (PMID: 18209781).

Animal data

Dogs. In 21 dogs that accidentally ate 5-HTP, 19 developed signs such as seizures, tremors, vomiting and high body temperature, resembling serotonin syndrome in people, and 3 died (PMID: 10863592). A 9-month-old Labrador developed serotonin syndrome after eating a 5-HTP supplement and recovered with treatment (PMID: 28210931).
Mice. In mice, 5-HTP, fluoxetine and the MAO inhibitor tranylcypromine each produced serotonin syndrome signs, and combining these drugs increased the effects (PMID: 24780865). Mice lacking both MAO A and MAO B genes had greatly exaggerated serotonin syndrome behavior after 5-HTP (PMID: 22964922).

Gaps

No human safety data on 5-HTP in pregnancy or breastfeeding were found. Most controlled trials summarized on this page lasted 12 weeks or less; the longest was a 1-year alcoholism trial that combined 5-HTP with carbidopa (PMID: 1424429).

On PubMed

The search 5-hydroxytryptophan[Title] OR 5-HTP[Title] OR oxitriptan[Title] on PubMed.

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03Safety

5-HTP side effects and interactions

Side effects

Common

Nausea and vomiting rising with dose: dropout of 6.6 percent at 100 mg and 45.5 percent at 300 mg with carbidopa in healthy men (PMID: 18308795)
Fatigue, nausea or vomiting in 19.6 percent of the 5-HTP group after a single dose in a 112-adult trial (PMID: 42160304)
Gastrointestinal side effects tracking plasma 5-HTP levels (PMID: 6187038)

Serious events

Eosinophilia-myalgia syndrome in one member of a family exposed to an impure 5-HTP batch, and high eosinophil counts in two others (PMID: 7699627)
Scleroderma-like illness during L-5-HTP and carbidopa treatment for myoclonus (PMID: 6997735)
Memory loss with MRI changes suggesting hippocampal ischemia after an accidental tenfold overdose, with recovery (PMID: 35878559)
Hypomania after starting 5-HTP with SAM-e (PMID: 29955516)
Serotonin syndrome-like poisoning in dogs, with 3 deaths among 21 cases (PMID: 10863592)

Who should not use it

Contraindications

Serotonergic antidepressants (SSRIs). In healthy men, 5-HTP strengthened the hormonal response to the SSRI citalopram (PMID: 16378695), and in depressed patients the hormonal response to 5-HTP was larger in those taking fluoxetine than in those on tricyclic antidepressants or no medication (PMID: 9194044). In mice, ordinary 5-HTP given with an SSRI caused marked adverse effects (PMID: 26932820). A 2006 review of 5-HTP safety emphasized serotonin syndrome as well as EMS (PMID: 16023217).

Read all the contraindications and cautionsShow less

MAO inhibitors. In mice, 5-HTP and the MAO inhibitor tranylcypromine each produced serotonin syndrome signs, and combinations of such serotonin-raising drugs increased them (PMID: 24780865). Mice lacking MAO enzymes reacted to 5-HTP with exaggerated serotonin syndrome behavior (PMID: 22964922).

Carbidopa. Carbidopa multiplies 5-HTP exposure: in 12 healthy men it doubled the half-life and raised total exposure 15.4 times (PMID: 11910264). A scleroderma-like illness was reported with the L-5-HTP and carbidopa combination (PMID: 6997735).

Mood switching. Hypomania was reported in a man taking 5-HTP with SAM-e for depression (PMID: 29955516).

Carcinoid tumor testing. 5-HTP raises urinary 5-HIAA, which is commonly measured to detect carcinoid tumors, and the authors of that study advised ruling out over-the-counter 5-HTP as the cause of a raised 5-HIAA before tests for a carcinoid tumor begin (PMID: 18209781).

Product quality. Contaminants of the peak X family have been found in commercial 5-HTP (PMID: 10721089, PMID: 12508395), and an EMS-related illness was reported with an impure batch (PMID: 7699627).

Pets. 5-HTP supplements eaten by dogs have caused serotonin syndrome-like illness and deaths (PMID: 10863592, PMID: 28210931).

Pregnancy and breastfeeding. No human safety data were found.

Interactions

4 pairings in our record: 3 with a caution and 1 to monitor.

SSRIs and other serotonin reuptake inhibitors
Caution

5-HTP strengthened the hormonal response to citalopram in healthy men (PMID: 16378695), and fluoxetine enlarged the hormonal response to 5-HTP in depressed patients (PMID: 9194044). In mice, ordinary 5-HTP given with an SSRI caused marked adverse effects (PMID: 26932820).
MAO inhibitors
Caution

In mice, 5-HTP and the MAO inhibitor tranylcypromine each produced serotonin syndrome signs, and combinations of such serotonin-raising drugs increased them (PMID: 24780865). Mice lacking MAO enzymes had exaggerated serotonin syndrome behavior after 5-HTP (PMID: 22964922).
SAM-e
Caution

A 42-year-old man developed hypomania about a week after starting 5-HTP together with SAM-e for depression (PMID: 29955516).
Carbidopa
Monitor

Carbidopa doubled the half-life of 5-HTP and raised its exposure 15.4 times in 12 healthy men (PMID: 11910264), and a scleroderma-like illness was reported with the combination (PMID: 6997735).

This interaction data is compiled from published research and community reports. It may not be exhaustive. Always consult a healthcare professional before combining compounds.

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04Dosing

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Dosing

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Our record lists no dose for 5-HTP (5-hydroxytryptophan). This section holds what it does list.

Dosing summary

Route: Oral, Intravenous

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05Prices

5-HTP (5-hydroxytryptophan) prices

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06Chemistry

Chemistry and structure

Molecular formula: C11H12N2O3
Molecular mass: 220.22 g/mol
CAS number: 4350-09-8
Half-life: About 2.2 to 7.4 hours in five healthy volunteers pretreated with carbidopa (PMID: 6187038), and about 6 hours after intravenous dosing in five carbidopa-pretreated patients (PMID: 311987). Carbidopa changes the kinetics: in 12 healthy men it doubled the elimination half-life of a 100 mg oral dose (PMID: 11910264).

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08Questions

Frequently asked questions

What is 5-HTP?

5-HTP (5-hydroxytryptophan) is an amino acid that the body makes from tryptophan and then converts to serotonin and melatonin (PMID: 33375373). 5-HTP sold as a supplement is the L form, and commercial 5-HTP has been extracted from the seeds of the West African plant Griffonia simplicifolia (PMID: 33375373, PMID: 33991640, PMID: 24936877).

Is 5-HTP a supplement or a prescription drug?

5-HTP is sold in the United States as a dietary supplement (PMID: 15068828). 5-HTP is not an FDA-approved drug: a Drugs@FDA search on 25 October 2026 found no application for oxitriptan or hydroxytryptophan. In Italy, 5-HTP is an authorized prescription medicine under the drug name oxitriptan, according to the Italian Medicines Agency database checked on 25 October 2026.

Does 5-HTP help depression?

The 2002 Cochrane review found 108 trials of 5-HTP or tryptophan for depression but only 2, with 64 patients, of good enough quality, and judged the evidence inconclusive (PMID: 11869656). A 2020 meta-analysis of 13 studies of 5-HTP in depression reported a pooled remission rate of 0.65 but rated the studies as weak because few had placebo groups (PMID: 31504850). In an Indian trial without placebo, 5-HTP and fluoxetine lowered depression scores by similar amounts (PMID: 23380314).

Is 5-HTP linked to eosinophilia-myalgia syndrome?

The 1989 eosinophilia-myalgia syndrome epidemic, with 1,531 US cases and 27 deaths reported by July 1990, was linked to manufactured L-tryptophan, the precursor of 5-HTP (PMID: 2398610, PMID: 33375373). A family exposed to an impure batch of 5-HTP included one member with eosinophilia-myalgia syndrome and two with high eosinophil counts (PMID: 7699627). Mayo Clinic chemists found peak X contaminants in commercial 5-HTP samples (PMID: 10721089, PMID: 12508395), while a 2004 review argued that no definitive case of 5-HTP toxicity had been shown (PMID: 15068828).

Can 5-HTP cause serotonin syndrome?

In mice, 5-HTP, fluoxetine and the MAO inhibitor tranylcypromine each produced serotonin syndrome signs, and combining these serotonin-raising drugs with one another increased the effects (PMID: 24780865). Dogs that accidentally ate 5-HTP supplements developed an illness resembling serotonin syndrome, and 3 of 21 dogs in one series died (PMID: 10863592). In people, 5-HTP strengthened the hormonal response to the SSRI citalopram (PMID: 16378695). In a 44-year-old man who took a tenfold 5-HTP overdose, doctors found no features of serotonin toxicity, although he developed memory loss (PMID: 35878559).

What side effects has 5-HTP shown in trials?

In a challenge study of 5-HTP given with carbidopa, nausea and vomiting were the most frequent side effects and rose with dose, causing 6.6 percent of healthy men to drop out at 100 mg and 45.5 percent at 300 mg (PMID: 18308795). After one dose of 5-HTP in a 112-adult trial, 19.6 percent of the participants given 5-HTP reported fatigue, nausea or vomiting (PMID: 42160304). 5-HTP also raises urinary 5-HIAA, which can give a false-positive result on a carcinoid tumor screening test (PMID: 18209781).

What else has 5-HTP been tested for?

Small 5-HTP trials have reported fewer sleep terrors in children, lower food intake and weight in obese adults, and improved fibromyalgia measures (PMID: 15146330, PMID: 1384305, PMID: 2193835). 5-HTP did not beat placebo for fatigue in a 166-patient inflammatory bowel disease trial or for menopausal hot flashes in 24 women (PMID: 35940251, PMID: 20031347).

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