5-HTP

Systematic reviews of 5-HTP have focused on people diagnosed with depression [1][2]. This page grades outcomes from trials that did not recruit a diagnosed clinical population, and those trials are few and small. The evidence grading method explains what each grade requires.

Does 5-HTP affect mood in healthy people?

The controlled evidence in people without a diagnosis points to no clear effect [5][4]. In a trial in 46 healthy undergraduates, each given either two 50 mg capsules of 5-HTP or placebo, 5-HTP did not significantly change mood ratings [5]. It did impair performance on a gambling task that measures decision making under ambiguity [5].

In a 12-week randomized trial in 30 cognitively healthy older adults in Singapore, 100 mg a day was compared with taking nothing in a single-blinded design without a placebo [4]. Scores on a mood questionnaire for older adults fell within the 5-HTP group between week 0 and week 8 (1.2 to 0.7 points), but the difference between groups over time was not significant (p = 0.3851), and anxiety scores did not change [4]. The study was funded by a National University of Singapore grant [4].

In a placebo-controlled crossover trial in 166 people with inactive inflammatory bowel disease and fatigue, a clinical population, 100 mg twice daily for 8 weeks did not change mood, anxiety or stress scores compared with placebo [8]. Results in clinical groups may not apply to healthy adults.

Population context only: in people diagnosed with depression, a clinical population, a 2002 Cochrane review of 5-HTP and tryptophan found only two of 108 located trials, with 64 patients in total, met its quality criteria; analyzed together with tryptophan, those trials suggested benefit over placebo, but the review judged the evidence insufficient to be conclusive [2]. A 2020 meta-analysis of 7 studies reported a large effect on questionnaire scores (Hedges' g 1.11) with high heterogeneity (I2 = 76%), and said current studies are relatively weak, with few placebo groups [1]. These findings do not apply to mood in healthy people.

Does 5-HTP improve sleep quality?

The only trial we could assess is small and had no placebo [3]. In a single-blinded, 12-week randomized trial, 30 older adults in Singapore were assigned to 100 mg of 5-HTP a day or nothing, and sleep was measured every 4 weeks by questionnaire and by a wrist activity monitor [3]. The authors report a favorable effect on certain sleep quality components, and the improvement in the overall sleep score was seen in poor sleepers rather than good sleepers [3]. The trial was funded by the National University of Singapore and registered as NCT04078724 [3].

The cognition and mood paper described above reports the same registered trial (NCT04078724), so the two papers count as one trial here [3][4]. As of November 11, 2026, our PubMed and Europe PMC searches found no placebo-controlled trial of 5-HTP reporting sleep quality in adults without a sleep or medical diagnosis. A 1971 study of 5-HTP and sleep in healthy subjects has no abstract in PubMed and was not assessed. A review notes that 5-HTP is associated with more rapid eye movement (REM) sleep [15]. See our sleep hub for other compounds.

Does 5-HTP improve attention?

In the one placebo-controlled trial, a single dose showed no significant benefit on the distractibility measures tested [6]. A randomized, double-blind, placebo-controlled trial gave 112 adults, 56 with high and 56 with low levels of self-reported attention-deficit traits, a single 200 mg dose of 5-HTP or placebo, then repeated two distraction tasks 90 minutes later [6]. 5-HTP produced no significant positive effect on any measure of distractibility, the trial's primary outcome [6]. On one task measure, the placebo group improved on retesting and the 5-HTP group did not [6]. One of the two tasks did not produce the expected distraction effect, and the authors call for more sensitive measures [6].

Does 5-HTP affect global cognition?

The one trial shows no significant difference from the control group [4]. In the 12-week trial in 30 cognitively healthy older adults, scores on the Montreal Cognitive Assessment (MoCA), a screening test of overall cognition, rose in the 5-HTP group from 26.6 to 27.6 [4]. Scores also rose in the group that took nothing, to 27.3 at week 12, and the difference between groups over time was not significant (p = 0.9343) [4]. Cognition was a secondary outcome, and the authors say the results should be interpreted cautiously given the sample size of 30 and the 12-week duration [4].

Does 5-HTP affect lean mass?

No change in lean mass was found in the one placebo-controlled trial [7]. In an 8-week trial, 48 exercise-trained men and women were randomized to 100 mg of 5-HTP a day (31 people) or a maltodextrin placebo (17 people), with body composition measured by bioelectrical impedance [7]. Lean body mass, total body water and percentage body fat did not change significantly in either group [7]. Fat mass changed more in the 5-HTP group than with placebo (p = 0.048), which the authors describe as limited data [7]. The trial was funded by the ingredient supplier NURA, whose CLEANMOOD 5-HTP ingredient was tested [7][28].

What the evidence does not show

Other trials in healthy adults measured laboratory tasks rather than everyday outcomes, and none of them grades an outcome on this page [9][10]. In a double-blind, placebo-controlled study of 77 healthy adults that tested a tryptophan-rich diet and, separately, an acute dose of 5-HTP, people rated immoral behavior without negative consequences as more reprehensible after 5-HTP [9]. In 32 healthy volunteers given a laboratory panic challenge, panic rates after 200 mg of 5-HTP and after placebo did not differ significantly (19% and 44%, p = 0.13) [10]. In the bowel disease trial, 5-HTP raised blood levels of 5-HTP but did not reduce fatigue compared with placebo (35.6% and 37.6% of patients reached the target reduction) [8].

In one pharmacokinetic study, absorption was rather slow [13]. In five patients with myoclonic disorders, a clinical population, peak blood levels after oral 5-HTP came 1.8 to 3.3 hours after the dose, and 47-84% of the dose reached the circulation [13]. In healthy volunteers, the half-life (the time to clear half of it) ranged from 2.2 to 7.4 hours [12]. Both studies gave 5-HTP with a decarboxylase inhibitor; with that pretreatment, about 48% of an oral dose reached the circulation in healthy volunteers [12][13]. The effect of the inhibitor on absorption is described under interactions [12].

Study protocols: in the Singapore trial, capsules were taken 20-30 minutes before bedtime [4], and in the attention trial, tasks were repeated 90 minutes after a single dose [6].

A trial, a review and Health Canada all describe gastrointestinal effects [6][15][21]. In the attention trial, 19.6% of people given a single 200 mg dose reported fatigue, nausea or vomiting, collected non-systematically from participant reports [6]. A review reports vomiting and nausea at doses above 100 mg, and says 5-HTP may cause dose-dependent gastrointestinal problems and, when combined with a decarboxylase inhibitor, psychological side effects such as acute anxiety [15]. In healthy volunteers, gastrointestinal side effects appeared related to 5-HTP blood levels [12]. Health Canada lists gastrointestinal discomfort as a known adverse reaction and asks labels to caution about driving because of possible drowsiness [21].

A review of 5-HTP research gives particular attention to two safety issues, serotonin syndrome and eosinophilia-myalgia syndrome (EMS) [14]. A review states that an excess of 5-HTP may be responsible for serotonin syndrome, which is marked by altered mental status, autonomic dysfunction and neuromuscular abnormalities [15]. Health Canada's monograph tells people to stop and ask a practitioner if they notice skin hardening, muscle or joint pain or stiffness, tremors, agitation or confusion, or a raised heart rate [21].

Memorial Sloan Kettering Cancer Center (MSKCC) notes that 5-HTP increases urine 5-HIAA excretion and serum chromogranin A (CgA) levels, which could lead to misinterpretation of those laboratory tests [27]. MSKCC lists nausea, vomiting and diarrhea as common side effects [27].

Concerns about contaminants began with tryptophan. Tryptophan supplements were suspended in 1989 after an outbreak of EMS, a rare and sometimes fatal condition, traced to contaminated tryptophan from a single manufacturer [15]. In a 1999 analysis, all eight commercial 5-HTP samples tested contained three or more contaminants of the "peak X" family, and EMS-like symptoms have been associated with 5-HTP exposure [16]. Another analysis, described in a 2020 review, identified peak X as 4,5-tryptophan-dione, a putative neurotoxin, and found it in six over-the-counter samples [15].

The evidence is contested. A 2004 safety review, whose first author is affiliated with a private laboratory, found no definitive cases of toxicity in 20 years of use, apart from one unresolved case, and said peak X lacks credibility because of chromatographic artifacts and tiny concentrations [17]. A Cochrane review says the possible link between 5-HTP or tryptophan and EMS has not been elucidated [2].

Interaction evidence comes from human studies, Health Canada and MSKCC. In a randomized challenge study in healthy Asian men, 200 mg of 5-HTP significantly augmented the hormone response (prolactin and cortisol) to the SSRI antidepressant citalopram [11]. Health Canada's monograph says not to use 5-HTP if taking antidepressants [21], and its food decision names possible interactions with monoamine oxidase inhibitors (MAOIs) and selective serotonin reuptake inhibitors (SSRIs) that may result in serotonin syndrome [22]. MSKCC reports a case of serotonin syndrome when 5-HTP was combined with linezolid, an antibiotic with MAOI activity, and a case of mania after 5-HTP was added to another MAOI [27]. MSKCC also says to avoid combining 5-HTP with other supplements that may affect serotonin levels, such as St John's wort or SAM-e [27].

Carbidopa changes how 5-HTP is handled. In healthy volunteers, carbidopa pretreatment significantly increased absorption of unchanged 5-HTP [12], and a review explains that decarboxylase inhibitors such as carbidopa block its conversion to serotonin outside the brain [14]. Health Canada also lists carbidopa, products with serotonergic activity, cough medicines containing dextromethorphan, pain killers, and medicines for nausea or migraine as reasons to ask a practitioner before use [21]. MSKCC reports a case of a scleroderma-like illness during combined use of carbidopa and 5-HTP [27].

If you take any of these medicines, talk to your doctor or pharmacist before combining them with 5-HTP.