Drug & supplement interaction

Black Horehound + Carbidopa, Levodopa, Entacapone

Carbidopa, Levodopa, Entacapone brand name: Stalevo.

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

Black Horehound has a moderate interaction with Carbidopa, Levodopa, Entacapone. Theoretically, black horehound might have additive effects when used with dopamine agonists.

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

Black Horehound and Carbidopa, Levodopa, Entacapone

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

Moderate

DOPAMINE AGONISTS

Why this applies to Carbidopa, Levodopa, Entacapone

Carbidopa, Levodopa, Entacapone falls under DOPAMINE AGONISTS — the group Black Horehound interacts with.

Theoretically, black horehound might have additive effects when used with dopamine agonists. Some constituents of black horehound bind to dopamine D2 receptors in vitro; however, this has not yet been reported in humans. Some dopamine agonists include bromocriptine (Parlodel), levodopa (Dopar, component of Sinemet), pramipexole (Mirapex), ropinirole (Requip), and others.
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 honest picture with Stalevo (the carbidopa, levodopa, and entacapone combo you take for Parkinson's). In test-tube studies, a few compounds in black horehound seem to latch onto dopamine D2 receptors, the same general targets your medication works through. The thinking is that the two could, in theory, add to each other's dopamine-like effects.

If that played out in the body, you might notice more of your usual Parkinson's medication effects, things like nausea, dizziness, lightheadedness when standing, or extra involuntary movements (dyskinesia). But I want to be clear: this has only been seen in lab dishes, never reported in real people. The evidence is very thin. Still, since both touch the same system, it's worth a quick word with your pharmacist or neurologist before adding this herb.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Daels-Rakotoarison DA, Seidel V, Gressier B, et al. Neurosedative and antioxidant activities of phenylpropanoids from Ballota nigra. Arzneimittelforschung 2000;50:16-23. 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

Black Horehound Also Interacts With Other Medications

Black Horehound has 22 moderate known drug interactions in our database — the Carbidopa, Levodopa, Entacapone one above is one of them. If you take anything else, check it against the full list below.

Moderate 22 No known interaction 2,808 (incl. Carbidopa, Levodopa, Entacapone)
Taking anything else?

Check Another of Your Medications Against Black Horehound

Covers the 2,830 medications we’ve checked against Black Horehound. Pick one to open its full report.

Everything else you take

See Every Supplement That Interacts With Carbidopa, Levodopa, Entacapone

This page covers Black Horehound only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Carbidopa, Levodopa, Entacapone page lists 55 supplements it has a documented interaction with, worst first, each one explained.

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

By severity: 8 major · 35 moderate · 12 minor.

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

“Most of what appears on this list works against Stalevo (carbidopa, levodopa, entacapone), the combination pill for Parkinson's disease, and that makes it a list worth genuine care. Everyday items like magnesium, iron, whey protein, and other amino acids can blunt levodopa's absorption or crowd it out of the brain, which shows up as wo…”

Reviewed by 2 · Jul 18, 2026

Open the Carbidopa, Levodopa, Entacapone interaction page

How much people look this up

Where Black Horehound and Carbidopa, Levodopa, Entacapone 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 Black Horehound
Top half

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

29 days ago today
Medication Carbidopa, Levodopa, Entacapone
Top 25%

#311 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 Black Horehound

What is Black Horehound?

Black Horehound
  • Nausea and vomiting
  • Anxiety and nervous tension
  • Sleep problems
  • Mild digestive upset
  • Coughs and respiratory complaints

Black horehound is a traditional European herb mainly used for nausea, mild anxiety, and digestive upset, but high-quality human studies are lacking, so its effectiveness is largely unproven. It has a strong, unpleasant smell and taste, and its safety has not been well studied, so it should be avoided in pregnancy and breastfeeding and used cautiously by everyone else.

Read the full Black Horehound monograph & all interactions
Keep checking

Other Drugs & Black Horehound

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

0Major
22Moderate
0Minor
2,807No known interaction
22 Moderate 2,807 No interaction
Moderate

22 interactions

No interaction 2,807 drugs checked — show the list

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

Showing the 60 most looked-up of 2,807 medications checked with no known interaction — see the full Black Horehound list.

See the full Black Horehound interactions page
See every supplement checked against Carbidopa, Levodopa, Entacapone, 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
Black Horehound monograph › Uses, safety, and every drug interaction in one place Carbidopa, Levodopa, Entacapone supplement interactions › Every supplement checked against Carbidopa, Levodopa, Entacapone, 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 Black Horehound and Carbidopa, Levodopa, Entacapone Together: Common Questions

Can you take Black Horehound with Carbidopa, Levodopa, Entacapone?
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 Black Horehound and Carbidopa, Levodopa, Entacapone 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 Carbidopa, Levodopa, Entacapone and Black Horehound?

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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.