Drug & supplement interaction

5-htp + Levodopa, Carbidopa

Levodopa, Carbidopa brand name: Duodopa.

Moderate Interaction
Medically reviewed by · Updated September 2026
The bottom line Moderate

5-htp has a moderate interaction with Levodopa, Carbidopa. Combining 5-HTP and carbidopa can increase the risk of serotonergic side effects.

Read the full interaction report
SeverityModerate
LikelihoodPossible
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

5-htp and Levodopa, Carbidopa

Here is the interaction we found between these two, with the evidence behind it.

Moderate

CARBIDOPA (Lodosyn)

Combining 5-HTP and carbidopa can increase the risk of serotonergic side effects.
Carbidopa is sometimes used with 5-HTP to minimize peripheral 5-HTP metabolism and boost the amount that reaches the brain. However, this combination might also increase the risk of some side effects including hypomania, restlessness, rapid speech, anxiety, insomnia, and aggressiveness. Combining carbidopa and 5-HTP might also increase the risk of scleroderma-like skin changes due to elevated serotonin levels.
Severity Moderate Likelihood Possible Evidence D

Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the key piece with your levodopa/carbidopa: the carbidopa part is the one that matters when 5-HTP is in the picture. Carbidopa blocks an enzyme outside the brain that normally breaks down compounds like 5-HTP. So when you add a 5-HTP supplement, carbidopa lets more of it slip through, which can push your serotonin levels higher than expected.

That extra serotonin is where the trouble can come from. People have reported things like restlessness, anxiety, racing or rapid speech, trouble sleeping, irritability, and feeling wound up or hypomanic. There are also rare reports of skin changes tied to high serotonin. This is based mostly on anecdotal reports, so it isn't certain, but it's worth taking seriously. Please check with your pharmacist or doctor before combining them rather than adjusting anything on your own.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Sternberg EM, Van Woert MH, Young SN, et al. Development of a scleroderma-like illness during therapy with L-5-hydroxytryptophan and carbidopa. N Engl J Med 1980;303:782-7. PubMed
  2. Iovieno, N., Dalton, E. D., Fava, M., and Mischoulon, D. Second-tier natural antidepressants: review and critique. J Affect.Disord. 2011;130(3):343-357. PubMed
  3. Van Woert, M. H., Rosenbaum, D., Howieson, J., and Bowers, M. B., Jr. Long-term therapy of myoclonus and other neurologic disorders with L-5- hydroxytryptophan and carbidopa. N Engl J Med 1-13-1977;296(2):70-75. PubMed
  4. van Hiele LJ. l-5-Hydroxytryptophan in depression: the first substitution therapy in psychiatry? The treatment of 99 out-patients with 'therapy-resistant' depressions. Neuropsychobiology 1980;6:230-40. PubMed

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

5-htp Also Interacts With Other Medications

5-htp has 397 moderate known drug interactions in our database — the Levodopa, Carbidopa one above is one of them. If you take anything else, check it against the full list below.

Moderate 397 No known interaction 2,433 (incl. Levodopa, Carbidopa)
Taking anything else?

Check Another of Your Medications Against 5-htp

Covers the 2,830 medications we’ve checked against 5-htp. Pick one to open its full report.

From our Q&A

Questions About 5-htp or Levodopa, Carbidopa

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers 5-htp or Levodopa, Carbidopa, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Levodopa, Carbidopa

This page covers 5-htp only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Levodopa, Carbidopa page lists 26 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Branched-chain Amino Acids (bcaa) (major), Cowhage (major), Indian Snakeroot (major), Magnesium (major) and Phenylalanine (major).

By severity: 7 major · 17 moderate · 2 minor.

From our pharmacist’s overview on the Levodopa, Carbidopa page

“Cowhage is the first thing to know here. It naturally contains levodopa, sometimes 75 to 400 mg per dose, so stacking it on Levodopa, Carbidopa (Duodopa) risks levodopa excess.”

Reviewed by 2 · Jul 18, 2026

Open the Levodopa, Carbidopa interaction page

One more smart check

Taking 5-htp as Part of a Dietary Supplement Product? Check It for Interactions

We hold 1,651 real supplement products containing 5-htp, each one broken down to its full ingredient list — and combination products often carry several ingredients besides 5-htp. Your product may carry other ingredients that interact with Levodopa, Carbidopa too, on top of 5-htp — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where 5-htp and Levodopa, Carbidopa Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement 5-htp
Top 10%

#121 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Levodopa, Carbidopa
Top 25%

#439 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Supplement

About 5-htp

What is 5-htp?

5-htp
  • Low mood or depression
  • Anxiety and stress
  • Sleep problems
  • Migraine headaches
  • Fibromyalgia
  • Appetite or weight management

5-HTP is a compound your body uses to make serotonin, and people take it as a supplement hoping to improve mood, sleep, and headaches. Some early research is promising, but the overall evidence is limited and not conclusive. Because it can affect serotonin and may interact with medicines, talk to your pharmacist or doctor before using it.

Read the full 5-htp monograph & all interactions
Keep checking

Other Drugs & 5-htp

Browse every other medication we’ve checked against 5-htp — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
397Moderate
0Minor
2,432No known interaction
397 Moderate 2,432 No interaction
Moderate

397 interactions

Showing 60 of 397 moderate interactions — see all 397 on the 5-htp page.

No interaction 2,432 drugs checked — show the list

We also checked 5-htp against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,432 medications checked with no known interaction — see the full 5-htp list.

See the full 5-htp interactions page
See every supplement checked against Levodopa, Carbidopa, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
5-htp monograph › Uses, safety, and every drug interaction in one place Levodopa, Carbidopa supplement interactions › Every supplement checked against Levodopa, Carbidopa, ranked by severity Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking 5-htp and Levodopa, Carbidopa Together: Common Questions

Can you take 5-htp with Levodopa, Carbidopa?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the 5-htp and Levodopa, Carbidopa interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Still Have a Question About Levodopa, Carbidopa and 5-htp?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.