The short answer
5-HTP may add to methadone-related drowsiness or impairment. Review co-use with the prescriber; an exact added risk or safe spacing interval has not been established.
What this answer covers
Oral L-5-hydroxytryptophan supplements.
- Supplement or preparation
- L-5-HTP
- Medication ingredient
- methadone
The supplement can affect alertness
The official 5-HTP monograph lists drowsiness as a possible effect.
Methadone adds a serious medication risk
Methadone has variable, prolonged effects and can impair breathing, especially with other CNS depressants. A general warning supports caution but does not provide this supplement pair’s event rate.
Product and treatment details matter
Dose, other medicines and the prescribed methadone formulation affect the assessment. The evidence does not establish a universal supplement dose limit or protective gap.
Keep changes coordinated with the prescriber
Tell the treatment team before adding or changing the supplement. Do not change methadone yourself. Avoid driving while impaired; slow breathing or unusual difficulty waking requires emergency help.
Evidence and practical considerations
Side effects & toxicity
Conditional additive-drowsiness precaution supported by exact methadone label and supplement-specific effects/guidance; current sedation claim not replaced by a different serotonin endpoint.
- Exact scope
- Oral L-5-hydroxytryptophan supplements. with Methadone6813 IN; exact oral hydrochloride preparation and injection distinguished; maintenance-study limits retained.
- Medication form and route
- oral medication; parenteral medication; oral supplement
What remains uncertain
- No unmeasured pair incidence, blanket class transfer or arbitrary spacing interval.
Factors that may matter: Preparation; Dose; Other medicines; Organ function.
Read the supporting source summaries
Source 1: current product label
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: People prescribed methadone
Long/variable elimination, respiratory depression, CNS-depressant and QT warnings; enzyme interactions including St John’s wort can change exposure.
How this applies: Exact methadone RxCUI 6813 IN, with stated salt/formulation/route bridge.
Not interchangeable administration with swallowed tablets, concentrates or injection; opioid-use-disorder care must remain supervised.
Source 2: current product label
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: People prescribed methadone
CNS-depressant and metabolic interaction precautions; individual dose and response vary.
How this applies: Exact methadone RxCUI 6813 IN, with stated salt/formulation/route bridge.
Oral grapefruit studies do not establish an injected-drug intestinal interaction.
Source 3: regulatory supplement monograph
webprod.hc-sc.gc.ca · Source check Sep 10, 2026
Population: Adult oral 5-HTP users
Consult before serotonergic co-use; possible drowsiness. Dextromethorphan-containing cough medicine specifically named among serotonergic products.
How this applies: Original source interpreted for methadone only within the stated preparation and endpoint limits.
Not a direct methadone combination trial; original preparation, dose and endpoint limits apply. No exact-pair adverse-event rate or protective spacing established.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Prepared exact methadone article with formulation-specific evidence and uncertainty. | |
| Research summary published |
Article revision: a76fae86b7152650
This guide brings together the evidence records used by our interaction checker. Each finding retains its own preparation limits, research date, and source summaries.
Full citations require verification. Reading this answer and the source summaries does not.
Taking other supplements or medications?
Use the checker to explore your other combinations. Ask a pharmacist to review the exact products, amounts and medical conditions in your complete list.
Open the interaction checkerInformation, not medical advice. Do not change prescribed treatment based on this guide.