Drug & supplement interaction

Syrian Rue + Tolcapone

Tolcapone brand name: Tasmar.

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

Tolcapone falls into 2 drug categories that Syrian Rue can interact with; the most serious is rated moderate. Theoretically, high doses of Syrian rue might increase the risk of liver damage when taken with hepatotoxic drugs.

Read the full interaction report
SeverityModerate
LikelihoodPossible
Interactions2
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Syrian Rue and Tolcapone

These two interact in 2 distinct ways. Each one is explained separately below.

Why Are There 2 Interactions?

Syrian Rue interacts with whole categories of medication. Tolcapone falls into 2 of those categories, so it can interact with Syrian Rue in 2 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Moderate).

Moderate

HEPATOTOXIC DRUGS

1 of 2

Why this applies to Tolcapone

Tolcapone falls under HEPATOTOXIC DRUGS — the group Syrian Rue interacts with.

Theoretically, high doses of Syrian rue might increase the risk of liver damage when taken with hepatotoxic drugs.
Cases of hepatotoxicity and hepatic failure have been reported in patients who ingested a large quantity (up to 100 grams) of Syrian rue seeds.
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 thing to know about tolcapone (Tasmar): it carries a built-in warning for liver injury, which is why your doctor checks your liver enzymes regularly while you take it. The concern with Syrian Rue isn't about it speeding up or slowing down how your body handles tolcapone. Instead, it's about stacking two stresses on the same organ. Large amounts of Syrian rue seeds (people have reported problems after eating up to 100 grams) have been linked to liver damage on their own.

Pairing something already hard on the liver with a drug that can be hard on the liver could, in theory, raise your risk of trouble like fatigue, yellowing skin or eyes, dark urine, or belly pain. This is a theoretical concern based on how each one behaves, not proven cases of the two together. Still, given tolcapone's liver reputation, I'd skip the Syrian rue and check with your doctor or pharmacist first.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Yuruktumen, A., Karaduman, S., Bengi, F., and Fowler, J. Syrian rue tea: a recipe for disaster. Clin Toxicol (Phila) 2008;46(8):749-752. PubMed
  2. Berdai MA, Labib S, Harandou M. Peganum harmala L. Intoxication in a Pregnant Woman. Case Rep Emerg Med 2014;2014:783236.
  3. Ghizlane EA, Manal M, Ines HA, et al. Fatal poisoning of pregnant women by peganum harmala L.: a case reports. Ann Med Surg (Lond) 2021;68:102649. PubMed
  4. Durmaz Çelik N, Ger Akarsu F, Ozkan S, Özdemir AÖ, Aykac Ö, Memmedova F. Herbal teas can be harmful: a case of Peganum harmala induced coma in a patient with Parkinson's disease. Neurocase 2021;27(2):117-119.
Moderate

DOPAMINE AGONISTS

2 of 2

Tolcapone also falls under DOPAMINE AGONISTS.

Theoretically, Syrian rue might increase the adverse effects of dopamine agonists.
Syrian rue contains the constituent harmine. Animal research shows that harmine increases extracellular dopamine levels. The clinical significance of this effect is unclear.
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 simple version. Tolcapone (Tasmar) works alongside your levodopa/carbidopa to help more dopamine reach your brain, which eases Parkinson's symptoms. Syrian Rue contains harmala alkaloids that, at least in animal studies, can also push dopamine levels up. Stacking two things that both raise dopamine could, in theory, amplify the usual dopamine-related side effects you might already notice with this regimen, like nausea, dizziness, low blood pressure when you stand, trouble sleeping, vivid dreams, or extra involuntary movements (dyskinesias).

I want to be honest with you: this is a theoretical concern based on lab work, not proven in people, so the real-world risk is uncertain. Still, since these alkaloids also act as MAO inhibitors, please don't combine them without first checking with your doctor or pharmacist.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Iurlo, M., Leone, G., Schilstrom, B., Linner, L., Nomikos, G., Hertel, P., Silvestrini, B., and Svensson, H. Effects of harmine on dopamine output and metabolism in rat striatum: role of monoamine oxidase-A inhibition. Psychopharmacology (Berl) 2001;159(1 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

Syrian Rue Also Interacts With Other Medications

Syrian Rue has 1,121 moderate known drug interactions in our database — the Tolcapone one above is among them. If you take anything else, check it against the full list below.

Moderate 1,121 No known interaction 1,709 (incl. Tolcapone)
Taking anything else?

Check Another of Your Medications Against Syrian Rue

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

Everything else you take

See Every Supplement That Interacts With Tolcapone

This page covers Syrian Rue only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Tolcapone page lists 58 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Beer (major), Siberian Cocklebur (major), Wine (major) and Ashwagandha (moderate).

By severity: 4 major · 45 moderate · 9 minor.

Open the Tolcapone interaction page

How much people look this up

Where Syrian Rue and Tolcapone 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 Syrian Rue
Steady interest

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

29 days ago today
Medication Tolcapone
Steady interest

#2,603 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 Syrian Rue

What is Syrian Rue?

  • Traditional remedy for digestive complaints
  • Used as a sedative or for mood
  • Antimicrobial and antiparasitic folk use
  • Used as a dye and incense
  • Recreational psychoactive use

Syrian Rue (Peganum harmala) is a traditional plant whose seeds contain potent compounds called harmala alkaloids, including MAO-inhibiting harmine and harmaline. There is little reliable human evidence that it safely treats any condition, and it carries real risks of toxicity, so it is not recommended for self-treatment. Talk to a pharmacist or doctor before considering it.

Read the full Syrian Rue monograph & all interactions
Medication

About Tolcapone

What Is Tolcapone Used For?

Brand name: Tasmar

Tolcapone tablets are used as an add-on treatment to levodopa and carbidopa for idiopathic Parkinson's disease (Parkinson's disease with no known cause). Both Tasmar and tolcapone tablets (generic) carry this indication.

Because of a serious risk of liver failure, tolcapone is ordinarily reserved for patients who are experiencing symptom fluctuations — such as "wearing-off" episodes between doses — and who are not responding satisfactorily to, or are not appropriate candidates for, other add-on therapies.

See full Tolcapone drug information
Keep checking

Other Drugs & Syrian Rue

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

0Major
1,121Moderate
0Minor
1,708No known interaction
1,121 Moderate 1,708 No interaction
Moderate

1,121 interactions

Showing 60 of 1,121 moderate interactions — see all 1,121 on the Syrian Rue page.

No interaction 1,708 drugs checked — show the list

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

Showing the 60 most looked-up of 1,708 medications checked with no known interaction — see the full Syrian Rue list.

See the full Syrian Rue interactions page
See every supplement checked against Tolcapone, 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
Syrian Rue monograph › Uses, safety, and every drug interaction in one place Tolcapone supplement interactions › Every supplement checked against Tolcapone, ranked by severity Tolcapone drug information › The full plain-English guide to this medication 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 Syrian Rue and Tolcapone Together: Common Questions

Can you take Syrian Rue with Tolcapone?
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.
Why are there 2 interactions listed for Syrian Rue and Tolcapone?
Tolcapone belongs to more than one drug category, and Syrian Rue interacts with each of those categories a little differently. We list every one so nothing is missed — your overall risk is driven by the most serious of them.
How serious is the Syrian Rue and Tolcapone 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 Tolcapone and Syrian Rue?

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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.