People ask how long 5-HTP takes to work for one of three reasons: mood, sleep or appetite. The honest answer depends on which, and on how much weight a small and mostly old set of studies can carry. A dose is absorbed within hours, but the studies that reported benefits measured them over weeks, and the largest placebo-controlled trial we found showed none. Here is what each study measured, and when.

This article is educational and is not medical advice. Do not take 5-HTP if you take an antidepressant: Health Canada lists that combination as a contraindication because of the risk of serotonin syndrome. 5-HTP is not a substitute for prescribed treatment. If you have symptoms of depression, talk to a doctor. If you are thinking about suicide or are in crisis, call or text 988 in Canada or the U.S., any time. If your safety is at risk right now, call 911.

The short answer

Expect hours for 5-HTP to be absorbed and weeks for anything else. In small absorption studies, blood levels peaked roughly two to three hours after a dose. A depression trial without a placebo group saw scores start to fall at week 2, the appetite trials ran 2 to 12 weeks, and the one recent sleep trial reported its result at week 12. The largest placebo-controlled trial we found, in 166 people, showed no difference from placebo after 8 weeks on fatigue, depression, anxiety or stress.

How fast it is absorbed

Two small studies from the early 1980s measured 5-HTP in the blood. In five patients taking it daily, levels peaked 1.8 to 3.3 hours after a dose, and on average about 69% of each dose reached the bloodstream (Magnussen 1980). In five healthy volunteers, the half-life, the time it takes blood levels to fall by half, ranged from 2.2 to 7.4 hours (Westenberg 1982). Both studies gave 5-HTP with carbidopa or a similar drug, which slows its breakdown outside the brain, so a plain supplement may behave somewhat differently. The broad picture still holds: 5-HTP is absorbed and cleared within hours, and some trials split the daily amount, for example into 100 mg twice a day (Truyens 2022).

Both studies also tied stomach side effects to dose. Gastrointestinal effects appeared to track the level of 5-HTP in the blood (Westenberg 1982), and nausea and vomiting appeared in a few cases while doses were being built up, which led the authors to stress starting slowly (Magnussen 1980). In the first days, nausea is a more likely thing to notice than any change in mood.

What a single dose has shown

The clearest single-dose result comes from a laboratory test of panic. In 24 people with panic disorder and 24 healthy volunteers, a single 200 mg dose of 5-HTP, compared with placebo, reduced the panic response to a lab test in which people inhale a gas mixture containing 35% carbon dioxide, but only in the people with panic disorder (Schruers 2002). That shows 5-HTP can act in the brain within hours of a dose. It does not show that one dose lifts everyday mood or treats anxiety, and it was a supervised research procedure, not a home routine.

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Mood: weeks, and weak evidence

A 2013 trial in India compared 5-HTP with the antidepressant fluoxetine in people with a first episode of depression. Among the 60 who completed it, depression scores fell by similar amounts in both groups, starting at week 2 and continuing through week 8 (Jangid 2013). There was no placebo group, and placebo groups in depression trials often improve too, so the trial can't show how much of that early change came from 5-HTP. A small placebo-controlled crossover trial in 25 people with Parkinson's disease reported lower clinician-rated depression scores during four weeks of 50 mg a day (Meloni 2020).

The largest placebo-controlled trial we found showed nothing. In 166 people whose inflammatory bowel disease was in remission but who still had fatigue, 100 mg twice a day for 8 weeks raised blood levels of 5-HTP and serotonin, yet fatigue, depression, anxiety and stress scores improved no more than with placebo (Truyens 2022). It was a fatigue trial, not a depression trial, but it is the biggest test of 5-HTP against placebo we found. The reviews land in the same cautious place. A Cochrane review located 108 trials of 5-HTP or tryptophan for depression, found only two, with 64 patients, of high enough quality to include, and judged the evidence insufficient to be conclusive (Shaw 2001). A 2020 meta-analysis described the 5-HTP studies as relatively weak, with few placebo groups (Javelle 2020).

Sleep: a 12-week result, without a placebo

Evidence for sleep in adults is thin. In a 12-week trial in Singapore, 30 adults with an average age of 66 took 100 mg of 5-HTP a day or nothing; there was no placebo. Sleep was checked every four weeks, and the published summary reports the main result at week 12: people who started as poor sleepers rated their sleep better, while good sleepers did not (Sutanto 2024). A second report from the same trial found slightly lower depression scores at week 8, from a low starting point (Li 2025). An older study gave 5-HTP at bedtime to children with sleep terrors under specialist care, and its results don't translate to adult insomnia (Bruni 2004).

Appetite: weeks, at doses above Canadian limits

Three trials by one research group in Rome tested 5-HTP for appetite in people with obesity, at 750 to 900 mg a day or about 8 mg per kilogram of body weight. Participants ate less and lost weight over study periods of two to six weeks (Ceci 1989; Cangiano 1992; Cangiano 1998). Those doses are roughly two to three times the 300 mg a day that Health Canada's monograph allows for mood, and they come from a single group's work, so they are not a guide to what a typical supplement will do.

What to expect, week by week

  • First hours: 5-HTP is absorbed and peaks in the blood within a few hours. Nausea is the effect you are most likely to notice this early.
  • Weeks 1 to 2: the usual window for building up from a low dose. The depression trial without a placebo group saw scores begin to fall at week 2, a point at which placebo groups often improve too.
  • Weeks 4 to 8: the span of the placebo-controlled trials. A small trial in Parkinson's disease found lower depression scores at four weeks; the largest trial we found showed no benefit at eight.
  • Week 12: when the recent sleep trial reported better sleep in poor sleepers, against a no-treatment group rather than a placebo.
  • Beyond 12 weeks: little data. One open study in fibromyalgia ran for 90 days and reported improvement throughout, with side effects in 30% of participants (Sarzi Puttini 1992). Past this point, review with a clinician whether to continue.

Before you think about timing: who should not take it

  • Anyone taking an antidepressant. Health Canada lists this as a contraindication: do not use 5-HTP with one. Both raise serotonin activity, and together they risk serotonin syndrome.
  • Other drugs that raise serotonin, such as triptans for migraine, tramadol and dextromethorphan, carry the same kind of risk. Check with a pharmacist before combining.
  • Carbidopa, a Parkinson's medication: only with your prescriber's oversight.
  • Scleroderma: Health Canada lists it as a contraindication.
  • Pregnancy or breastfeeding: not without a clinician's guidance.
  • 5-HTP can cause drowsiness, so take care with driving or machinery until you know how it affects you.

Health Canada's monograph also lists symptoms that mean stop taking it and seek advice: hardening of the skin, muscle or joint pain or stiffness, tremor, agitation, confusion, or a faster heart rate. Tremor, agitation, confusion and a racing heart can be signs of too much serotonin. The skin and muscle symptoms recall eosinophilia-myalgia syndrome, a serious illness traced in 1989 to contaminated L-tryptophan from one manufacturer (Das 2004), and later reported in a family whose 5-HTP contained an impurity (Michelson 1994). Cases linked to 5-HTP are rare, but those symptoms are a reason to stop and get checked promptly.

If you decide to try it

  • Start low and build up slowly. Nausea is the most common side effect, and it is tied to dose.
  • Stay within the label. Health Canada's monograph allows 150 to 300 mg a day for mood and 100 to 200 mg a day for sleep, with no more than 300 mg in a single dose.
  • Note how you feel or sleep before you start, then judge it after 8 to 12 weeks rather than day to day.
  • If nothing has changed by then, it is reasonable to conclude it isn't helping and to stop.
  • Tell your doctor or pharmacist you take it, and mention it whenever a new medication is prescribed.

The bottom line

5-HTP is absorbed within hours, but the evidence for mood, sleep and appetite comes from studies of 2 to 12 weeks that are mostly small and often lack a placebo group, and the largest placebo-controlled trial we found showed no benefit at 8 weeks. If you try it, start low, stay within the label, and judge it at 8 to 12 weeks. Above all, don't combine it with an antidepressant, and don't use it in place of treatment for depression.

Evidence grade, Health Canada's dose limits, every caution and the references behind them, in one place. See the full 5-HTP profile

References

This article draws on the primary research below; see the linked studies for full methods and doses.

  • Magnussen I, Nielsen-Kudsk F. "Bioavailability and related pharmacokinetics in man of orally administered L-5-hydroxytryptophan in steady state." Acta Pharmacologica et Toxicologica, 1980;46(4):257–262. PMID: 6966118.
  • Westenberg HG, Gerritsen TW, Meijer BA, van Praag HM. "Kinetics of l-5-hydroxytryptophan in healthy subjects." Psychiatry Research, 1982;7(3):373–385. PMID: 6187038.
  • Schruers K, van Diest R, Overbeek T, Griez E. "Acute L-5-hydroxytryptophan administration inhibits carbon dioxide-induced panic in panic disorder patients." Psychiatry Research, 2002;113(3):237–243. PMID: 12559480.
  • Jangid P, Malik P, Singh P, Sharma M, Gulia AK. "Comparative study of efficacy of l-5-hydroxytryptophan and fluoxetine in patients presenting with first depressive episode." Asian Journal of Psychiatry, 2013;6(1):29–34. PMID: 23380314.
  • Meloni M, Puligheddu M, Carta M, et al. "Efficacy and safety of 5-hydroxytryptophan on depression and apathy in Parkinson's disease: a preliminary finding." European Journal of Neurology, 2020;27(5):779–786. PMID: 32067288.
  • Truyens M, Lobatón T, Ferrante M, et al. "Effect of 5-Hydroxytryptophan on Fatigue in Quiescent Inflammatory Bowel Disease: A Randomized Controlled Trial." Gastroenterology, 2022;163(5):1294–1305.e3. PMID: 35940251.
  • Shaw K, Turner J, Del Mar C. "Tryptophan and 5-hydroxytryptophan for depression." Cochrane Database of Systematic Reviews, 2001;(3):CD003198. PMID: 11687048.
  • Javelle F, Lampit A, Bloch W, et al. "Effects of 5-hydroxytryptophan on distinct types of depression: a systematic review and meta-analysis." Nutrition Reviews, 2020;78(1):77–88. PMID: 31504850.
  • Sutanto CN, Xia X, Heng CW, et al. "The impact of 5-hydroxytryptophan supplementation on sleep quality and gut microbiota composition in older adults: A randomized controlled trial." Clinical Nutrition, 2024;43(3):593–602. PMID: 38309227.
  • Li S, Sutanto CN, Xia X, Kim JE. "The Impact of 5-Hydroxytryptophan Supplementation on Cognitive Function and Mood in Singapore Older Adults: A Randomized Controlled Trial." Nutrients, 2025;17(17):2773. PMID: 40944161.
  • Bruni O, Ferri R, Miano S, Verrillo E. "L-5-Hydroxytryptophan treatment of sleep terrors in children." European Journal of Pediatrics, 2004;163(7):402–407. PMID: 15146330.
  • Ceci F, Cangiano C, Cairella M, et al. "The effects of oral 5-hydroxytryptophan administration on feeding behavior in obese adult female subjects." Journal of Neural Transmission, 1989;76(2):109–117. PMID: 2468734.
  • Cangiano C, Ceci F, Cascino A, et al. "Eating behavior and adherence to dietary prescriptions in obese adult subjects treated with 5-hydroxytryptophan." American Journal of Clinical Nutrition, 1992;56(5):863–867. PMID: 1384305.
  • Cangiano C, Laviano A, Del Ben M, et al. "Effects of oral 5-hydroxy-tryptophan on energy intake and macronutrient selection in non-insulin dependent diabetic patients." International Journal of Obesity and Related Metabolic Disorders, 1998;22(7):648–654. PMID: 9705024.
  • Sarzi Puttini P, Caruso I. "Primary fibromyalgia syndrome and 5-hydroxy-L-tryptophan: a 90-day open study." Journal of International Medical Research, 1992;20(2):182–189. PMID: 1521674.
  • Das YT, Bagchi M, Bagchi D, Preuss HG. "Safety of 5-hydroxy-L-tryptophan." Toxicology Letters, 2004;150(1):111–122. PMID: 15068828.
  • Michelson D, Page SW, Casey R, et al. "An eosinophilia-myalgia syndrome related disorder associated with exposure to L-5-hydroxytryptophan." Journal of Rheumatology, 1994;21(12):2261–2265. PMID: 7699627.
  • Health Canada. "5-HTP" natural health product monograph, 28 August 2024. webprod.hc-sc.gc.ca/nhpid-bdipsn