5-HTP

Is 5-HTP safe?

On its own and at the doses Canada licenses, 5-HTP is usually tolerated, with nausea and stomach upset the common complaints. The problem is what it does: it is converted straight into serotonin. That makes it a poor partner for antidepressants and several other common drugs, and Health Canada's rules for licensed products say plainly, "Do not use if you are taking antidepressants." It scores 60, about level with St John's wort, which has a similar serotonin problem plus many more drug interactions.

Can 5-HTP cause serotonin syndrome?

Yes, in combination. Serotonin syndromeSerotonin syndromeA reaction caused by too much serotonin in the body, usually from combining medicines that raise it. Symptoms range from shivering to high fever.More in the glossary happens when several drugs push serotonin up at once. Symptoms range from shivering, sweating and diarrhoea to agitation, muscle stiffness, high fever and seizures. Published human cases from 5-HTP alone are scarce, and some researchers argue the risk is overstated, but the mechanism is direct, and regulators treat it as real.

Health Canada's monograph for licensed 5-HTP products, updated in 2024, says:

• Do not use with antidepressants. That includes SSRIs such as sertraline, fluoxetine and escitalopram, as well as SNRIs, MAO inhibitors and tricyclics.
• Ask first if you take carbidopa (a Parkinson's drug), cough medicine with dextromethorphan, pain killers, or medicines for nausea or migraine. Among pain killers, tramadol is the best-known serotonin risk; triptans for migraine and ondansetron for nausea are others.
• Stop and get advice for tremor, agitation or confusion, a fast heart rate, muscle or joint pain and stiffness, or skin hardening.

Bupropion acts mainly on dopamine and noradrenaline rather than serotonin, but it is still an antidepressant, so the same rule applies: talk to your doctor or pharmacist before combining anything with it.

What doses does Health Canada allow?

Use (adults)	Daily dose
Sleep	100 to 200 mg
Mood	150 to 300 mg
Migraine prevention	200 to 600 mg
Fibromyalgia symptoms	300 to 400 mg
Weight management	750 to 900 mg

No single dose should exceed 300 mg. The monograph advises starting low and building up over two weeks to limit stomach side effects, taking it with food (except for weight-loss use, before meals), and taking care with driving because it can cause drowsiness. Weight-loss products above 600 mg a day carry an extra warning to ask a professional beyond 12 weeks.

US products are not bound by these limits. Supplements in the US do not need FDA approval for safety before sale, so check the dose on your product against these figures.

The contamination question

5-HTP carries an unusual history. In 1989 an outbreak of eosinophilia-myalgia syndrome, a serious illness of muscle pain and high white cell counts, was traced to contaminated L-tryptophan from a single manufacturer, and L-tryptophan supplements were withdrawn. 5-HTP filled the gap.

Then reports appeared. In 1994 researchers at the NIH described a family who fell ill after taking 5-HTP: one member had the syndrome and two had raised eosinophil counts, and their 5-HTP contained an impurity not found in other samples. Switching to a clean product resolved the blood changes. In 1999 a Mayo Clinic team found a family of "peak X" contaminants in all eight commercial 5-HTP samples it tested, and in 2003 it identified one as 4,5-tryptophan-dione, a putative neurotoxin, in six over-the-counterOver-the-counterA medicine you can buy without a prescription, in a pharmacy or shop, with directions on the pack for safe use without a doctor.More in the glossary products.

A 2004 review in Toxicology Letters disagreed, calling peak X a chromatographic artefact at tiny concentrations and noting no definitive cases of toxicity in 20 years of worldwide use, apart from one unresolved Canadian case. Both views are published, and we have found no recent independent testing to settle it. That uncertainty is why product quality scores only 55.

Health Canada's monograph also says not to use 5-HTP with scleroderma, after older reports of scleroderma-like illness.

Who should be careful

• Anyone on antidepressants, tramadol, triptans, dextromethorphan, ondansetron or carbidopa.
• People with depression, anxiety or bipolar disorder. Treating mood with a serotonin precursor alone is not a substitute for care.
• Pregnant or breastfeeding women.
• People with scleroderma.
• Anyone combining it with other mood supplements such as St John's wort.

If you take it, choose a product that states its 5-HTP content in milligrams and, where available, has a USP VerifiedThird-party testingTesting of a supplement by an independent lab to check that it contains what the label says and is free of set contaminants.More in the glossary or NSF mark. Stop and seek advice if you develop muscle pain, unusual tiredness or a rash.

How we scored it

Dose safety and organ toxicity (both 70) reflect mostly mild side effects and rare, contested cases of eosinophilia-myalgia-like illness. Interactions (35) is the weakest factor, because the antidepressant contraindicationContraindicationA situation in which a medicine should not be used, because the risk clearly outweighs any benefit, such as a known allergy to it.More in the glossary covers a large share of the people who look for mood supplements. Product quality (55) reflects the unresolved contaminant findings. For sleep, melatonin has fewer interaction worries.