5-HTP: The Precursor to Serotonin and 17 Things You Need to Know

5-Hydroxytryptophan (5-HTP) is an amino acid precursor of serotonin with anti-depressant, anti-anxiety, sleep, and weight loss benefits, but with some caveats. Read this post to learn more about the proven health benefits and risks of supplementing with 5-HTP.


5-hydroxytryptophan (5-HTP) is an amino acid that serves as a precursor for the biosynthesis of serotonin and melatonin in the brain from the other amino acid tryptophan.

Currently, depression is hypothetically described as caused by having low levels of serotonin in the brain, although we still don’t understand exactly what causes depression (R).

5-HTP in supplement form is extracted from the plant Griffonia simplicifolia, an African shrub.

5-HTP vs Tryptophan in Serotonin Metabolism

1) 5-HTP is Readily Made into Serotonin

The amino acid tryptophan is converted to 5-HTP before it is converted to serotonin. TPH1 and TPH2, the enzymes responsible for converting tryptophan to 5-HTP, is the slowest (rate-limiting) enzyme in serotonin production (R).

5-HTP is readily and freely converted to serotonin without biochemical inhibition.

2) 5-HTP Readily Crosses the Blood-Brain Barrier

Tryptophan competes with leucine, valine, tyrosine, and isoleucine to cross the blood-brain barrier through the large neutral amino acid (LNAA) receptors (R).

5-HTP, however, does not compete with other amino acids to enter the brain.

5-HTP readily crosses the blood-brain barrier without receptors or channels.

Serotonin does not cross the blood-brain barrier, so serotonin outside of the brain (in the gut, platelets, heart, and liver) stays separate from serotonin in the brain.

5-HTP gets converted into serotonin both inside and outside of the brain.

3) 5-HTP is Only Made into Serotonin

While tryptophan can be used for protein synthesis and turning into niacin, 5-HTP can only be used for converting into serotonin (R).

4) 5-HTP Bypasses Neurotoxic Tryptophan Metabolites

Tryptophan can be converted into kynurenic acid and quinolinic acid, which are involved in psychiatric disorders such as schizophrenia, anxiety, depression, and ADHD (R).

These conversions happen more in individuals with inflammation, which may be a link between inflammation and psychiatric or neurological disorders (R, R2, R3).

5-HTP is not directly converted into neurotoxic metabolites, but high levels of serotonin may cause a feedback that increases these metabolites (R).

Pharmacokinetics of 5-HTP

5-HTP is rapidly absorbed in the upper intestine, with 50% of 5-HTP absorbed in 1.5 hours (R).

Elimination of 5-HTP is also rapid, with 50% absorbed in 2 hours (R).

Due to the rapid pharmacokinetics of 5-HTP, slow-release supplementation of 5-HTP may be more beneficial to maintain serotonin levels in the brain (R).

About 70% of ingested 5-HTP is found in the bloodstream (R).

Patients who take 5-hydroxytryptophan have severely decreased levels of P450 expression, (R).

Health Benefits of 5-HTP Supplementation

5) 5-HTP may Help with Depression

Small clinical studies have shown that 5-HTP alleviates depression better than placebo. However, more large-scale and higher quality studies are necessary to confirm the safety and effectiveness of 5-HTP (R).

The antidepressant effects of 5-HTP are comparable to that of some antidepressants (R).

Combined treatments of 5-HTP and SSRI seems to have strong synergistic effects on serotonin levels in rats and humans so that some clinicians recommend the use of slow-released 5-HTP in combination with SSRIs (R, R2, R3). However, additional clinical trials are required to demonstrate the safety and effectiveness of this approach, and combinations of 5-HTP and medications should only be used under medical supervision.

In a small clinical trial involving 52 healthy male subjects, either oral 5-HTP or antidepressant enhanced serotonin levels by 35% and 100%, but a combination between antidepressant and 5-HTP by 500% (R).

6) 5-HTP Helps with Panic Attacks and Anxiety

In young adults who suffer stress or anxiety from unreciprocated romanticism, a 6-week supplementation of 5-HTP decreased anxiety in 3 weeks by increasing serum brain-derived neurotrophic factor levels and serotonin levels (R).

People who suffer from chronic panic attacks due to lower availability of serotonin in the brain found significant relief through supplementation of 200 mg of 5-hydroxytryptophan (R).

In human clinical trials, herbal extracts of 5-HTP were shown to increase GABA receptor agonists or increase GABA levels entirely, promoting a sense of relaxation and decreased anxiety (R).

7) 5-HTP Helps with Night Terrors in Children

Children aged 3-10 who suffer from sleep terrors nightly had a reduction of 93.5% after taking a supplement of 2 mg/kg every night before bed for a month (R).

8) 5-HTP Helps Reduce Appetite, Craving, and Weight Loss


Carbohydrate increases serotonin levels in the brain, so increasing serotonin levels, such as by supplementing with 5-HTP, can mitigate carbohydrate craving and appetite, thus helps with adherence to dietary interventions and weight loss (RR2).

In small clincial trials, 5-HTP supplementation in obese women resulted in no mood changes but decreased food intake and weight loss (R, R2).

9) 5-HTP Supports Successful Dietary Intervention in Type II Diabetes

In a 2-week long clinical trial involving 25 overweight diabetic subjects given no dietary restrictions, subjects who received 5-HTP had reduced caloric, carbohydrate, and fat intake comparing to placebo. Subjects who received 5-HTP also have reduced body weight, blood sugar, insulin and HbA1C levels after 2 weeks, possibly due to changes in the diet (R).

10) 5-HTP Helps Improve Sleep Quality


A human with a genetic mutation that causes serotonin deficiency lacks circadian rhythm and overeats. For this person, supplementation with 5-HTP restores normal circadian rhythm and food intake (R).

Over long periods of supplementation, natural transcription of GABA receptors increased which assisted with natural sleep cycles and promotion of healthy sleep (R).

A small clinical trial demonstrated that the use of 5-HTP in combination with GABA  significantly improves sleep quality in 9 subjects with sleep disorders, in comparison to placebo (R).

11) 5-HTP may Help Mitigate Neurological Symptoms of Phenylketonuria

5-HTP relieves neurological symptoms due to phenylketonuria in mice (R).

12) 5-HTP Helps Restore Serotonin Levels After a Spinal Cord Injury

In rats with simulated spinal cord injury, supplementation with 5-HTP restored normal levels of serotonin (R).

Risks and Side Effects of 5-HTP Supplementation

13) 5-HTP can Cause Nausea and Vomiting

Since serotonin in the digestive system controls gut movement, all interventions that increase serotonin levels, including 5-HTP supplementation and SSRI antidepressants, can cause nausea, vomiting, and diarrhea.

The most commonly reported side effects of 5-HTP in all clinical trials in humans are nausea and vomiting as the quick surge of serotonin throughout the body is not well tolerated (R, R2).

Slow-released 5-HTP may be better tolerated and less likely to cause side effects (R).

14) Long-Term Supplementation with 5-HTP can Deplete Dopamine, Norepinephrine, and Epinephrine

Serotonin shares the same conversion (AAAD) and breakdown enzyme (MAO) with catecholamine neurotransmitters (dopamine, norepinephrine, and epinephrine).

Long term supplementation of 5-HTP can cause imbalances of these neurotransmitters, which can worsen neurological and psychiatric diseases. It is therefore recommended that 5-HTP supplementation is supervised by qualified clinicians and balanced with catecholamine precursors (R).

15) 5-HTP and Serotonin Syndrome

Serotonin syndrome explains a set of symptoms caused by very high levels of serotonin, which can be very serious and life-threatening (R).

Mild symptoms include shivering, sweating, tremor, restless limbs, and headache. Serious symptoms include hypertension, fever, mania, hallucination, and ataxia (R).

Serotonin syndrome is almost exclusively caused by SSRI and MAOI combinations, causing excessive levels of serotonin in the brain (R).

5-HTP or 5-HTP in combination with SSRI has not been reported to cause serotonin syndrome (R, R2).

16) 5-HTP and Eosinophilia Myalgia Syndrome

Eosinophilia myalgia syndrome (EMS) is a disease causing severe, disabling, chronic muscle pain, skin symptoms, and other neurotoxic reactions which affected over 1500 people and caused at least 38 deaths. The FDA estimated that there are 10 EMS cases associated with 5-HTP worldwide (R).

It seems more likely that it is caused by a bacterial contamination in the supplement than tryptophan or 5-HTP itself. No new cases of supplement-related EMS has been reported since 1990 (R).

17) Other Side Effects

Other rare side effects of 5-HTP include hypomania, lightheadedness, headache, and heart palpitations (R, R2).



200 mg is safe and beneficial for increasing serotonin levels in the brain, although some studies have shown safety and effectiveness when titrating doses up to 3 grams per day (R). Higher dosages increase the likelihood of side effects.

In obesity and weight loss intervention studies, up to 900 mg or 8 mg/kg of body weight of 5-HTP was safely used for 2 weeks, although side effects of nausea and vomiting were reported (R, R2).



  • It is not possible to measure serotonin levels in a human brain without a brain biopsy. Surrogate markers that are good indicators of serotonin levels in the brain are glucocorticoid (cortisol) levels and blood or urinary HIAA levels (R, R2).
  • The absence of increased 5-HTP activity in the dorsolateral prefrontal cortices correlates with premenstrual irritability (R). While it is possible that 5-HTP supplementation may help with premenstrual symptoms, there is currently no clinical study available to support this benefit of 5-HTP.


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