Drug & supplement interaction

Milk Thistle + Dronabinol

Dronabinol brand names: Marinol, Syndros.

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

Dronabinol falls into 2 drug categories that Milk Thistle can interact with; the most serious is rated minor. It is unclear if milk thistle inhibits CYP2C9; research is conflicting.

Read the full interaction report
SeverityMinor
LikelihoodUnlikely
Interactions2
EvidenceB
What do Severity, Likelihood & Evidence mean?
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Interaction report

Milk Thistle and Dronabinol

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

Why Are There 2 Interactions?

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

Minor

CYTOCHROME P450 2C9 (CYP2C9) SUBSTRATES

1 of 2

Why this applies to Dronabinol

Dronabinol falls under CYTOCHROME P450 2C9 (CYP2C9) SUBSTRATES — the group Milk Thistle interacts with.

It is unclear if milk thistle inhibits CYP2C9; research is conflicting.
In vitro research suggests that milk thistle might inhibit CYP2C9. Additionally, 3 case reports from the World Health Organization (WHO) adverse drug reaction database describe increased toxicity in patients taking milk thistle and cancer medications that are CYP2C9 substrates, including imatinib and capecitabine. However, contradictory clinical research shows that milk thistle extract does not inhibit CYP2C9 or significantly affect levels of the CYP2C9 substrate tolbutamide. Differences in results could be due to differences in dosages or formulations utilized.
Severity Minor Likelihood Unlikely Evidence B

Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans..

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

Here's the gist: your body uses a liver enzyme called CYP2C9 to help clear dronabinol from your system. There's a theory that milk thistle might slow that enzyme down a bit. If that happened, dronabinol could linger a little longer and feel stronger, which might mean more drowsiness, dizziness, a foggy or 'high' feeling, or a faster heartbeat.

That said, I wouldn't lose sleep over this one. The evidence is genuinely mixed, with some lab hints and a few scattered case reports, but better-quality human studies suggest milk thistle doesn't meaningfully block CYP2C9. It's rated minor and unlikely. Still, since both can make you sleepy, just mention to your pharmacist or doctor that you're using milk thistle so they can keep an eye on how you feel.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Beckmann-Knopp S, Rietbrock S, Weyhenmeyer R, et al. Inhibitory effects of silibinin on cytochrome P-450 enzymes in human liver microsomes. Pharmacol Toxicol 2000;86:250-6. PubMed
  2. Gurley BJ, Gardner SF, Hubbard MA, et al. In vivo assessment of botanical supplementation on human cytochrome P450 phenotypes: Citrus aurantium, Echinacea purpurea, milk thistle, and saw palmetto. Clin Pharmacol Ther 2004;76:428-40. .
  3. Sridar C, Goosen TC, Kent UM, et al. Silybin inactivates cytochromes P450 3A4 and 2C9 and inhibits major hepatic glucuronosyltransferases. Drug Metab Dispos 2004;32:587-94. PubMed
  4. Doehmer J, Weiss G, McGregor GP, Appel K. Assessment of a dry extract from milk thistle (Silybum marianum) for interference with human liver cytochrome-P450 activities. Toxicol In Vitro 2011;25:21-7. PubMed
  5. Kawaguchi-Suzuki M, Frye RF, Zhu HJ, et al. The effects of milk thistle (Silybum marianum) on human cytochrome P450 activity. Drug Metab Dispos. 2014;42(10):1611-6. PubMed
  6. Pochet S, Lechon AS, Lescrainier C, et al. Herb-anticancer drug interactions in real life based on VigiBase, the WHO global database. Sci Rep 2022;12(1):14178. PubMed
Minor

CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES

2 of 2

Dronabinol also falls under CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES.

It is unclear if milk thistle inhibits CYP3A4; research is conflicting.
While laboratory research shows conflicting results, pharmacokinetic research shows that taking milk thistle extract 420-1350 mg daily does not significantly affect the metabolism of the CYP3A4 substrates irinotecan, midazolam, or indinavir. However, 8 case reports from the World Health Organization (WHO) adverse drug reaction database describe increased toxicity in patients taking milk thistle and cancer medications that are CYP3A4 substrates, including gefitinib, sorafenib, doxorubicin, and vincristine.
Severity Minor Likelihood Unlikely Evidence D

Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans..

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

Here's the short version: your body uses a liver enzyme called CYP3A4 to help clear dronabinol (Marinol, Syndros). In theory, if milk thistle slowed that enzyme down, dronabinol could hang around a bit longer and you might feel more of its effects, things like drowsiness, dizziness, a racing heart, confusion, or feeling unusually high or anxious.

The good news is that this concern is mostly on paper. The research is genuinely conflicting, and careful human studies found milk thistle did not meaningfully change how the body handles similar CYP3A4 medicines. So a real-world problem is unlikely. Still, if you notice extra grogginess or unease, or you just want peace of mind, run it by your pharmacist or doctor before combining them.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Venkataramanan R, Ramachandran V, Komoroski BJ, et al. Milk thistle, a herbal supplement, decreases the activity of CYP3A4 and uridine diphosphoglucuronosyl transferase in human hepatocyte cultures. Drug Metab Dispos 2000;28:1270-3. DOI
  2. Piscitelli SC, Formentini E, Burstein AH, et al. Effect of milk thistle on the pharmacokinetics of indinavir in healthy volunteers. Pharmacotherapy 2002;22:551-6. PubMed
  3. Sridar C, Goosen TC, Kent UM, et al. Silybin inactivates cytochromes P450 3A4 and 2C9 and inhibits major hepatic glucuronosyltransferases. Drug Metab Dispos 2004;32:587-94. PubMed
  4. van Erp NP, Baker SD, Zhao M, et al. Effect of milk thistle (Silybum marianum) on the pharmacokinetics of irinotecan. Clin Cancer Res 2005;11:7800-6.
  5. Budzinski JW, Trudeau VL, Drouin CE, et al. Modulation of human cytochrome P450 3A4 (CYP3A4) and P-glycoprotein (P-gp) in Caco-2 cell monolayers by selected commercial-source milk thistle and goldenseal products. Can J Physiol Pharmacol 2007;85:966-78.
  6. Doehmer J, Weiss G, McGregor GP, Appel K. Assessment of a dry extract from milk thistle (Silybum marianum) for interference with human liver cytochrome-P450 activities. Toxicol In Vitro 2011;25:21-7. PubMed
  7. Jalloh MA, Gregory PJ, Hein D, et al. Dietary supplement interactions with antiretrovirals: a systematic review. Int J STD AIDS. 2017 Jan;28(1):4-15. PubMed
  8. Kawaguchi-Suzuki M, Frye RF, Zhu HJ, et al. The effects of milk thistle (Silybum marianum) on human cytochrome P450 activity. Drug Metab Dispos. 2014;42(10):1611-6. PubMed
  9. Pochet S, Lechon AS, Lescrainier C, et al. Herb-anticancer drug interactions in real life based on VigiBase, the WHO global database. Sci Rep 2022;12(1):14178. 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

Milk Thistle Also Interacts With Other Medications

Milk Thistle has 254 moderate, 699 minor known drug interactions in our database — the Dronabinol one above is among them. If you take anything else, check it against the full list below.

Moderate 254 Minor 699 No known interaction 1,877 (incl. Dronabinol)
Taking anything else?

Check Another of Your Medications Against Milk Thistle

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

From our Q&A

Questions About Milk Thistle or Dronabinol

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Milk Thistle or Dronabinol, 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 Dronabinol

This page covers Milk Thistle only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Dronabinol page lists 151 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Grapefruit (major), St. John's Wort (major), Acacia Rigidula (moderate) and Adrafinil (moderate).

By severity: 3 major · 107 moderate · 41 minor.

From our pharmacist’s overview on the Dronabinol page

“A glass of grapefruit juice can push dronabinol (Marinol, Syndros), the prescription form of THC used for chemotherapy nausea and appetite loss, to higher blood levels than intended, amplifying dizziness, sedation, and its mind-altering effects. That is one of three major-rated interactions among the 151 supplements and herbs on file,…”

Reviewed by 2 · Jul 18, 2026

Open the Dronabinol interaction page

One more smart check

Taking Milk Thistle as Part of a Dietary Supplement Product? Check It for Interactions

We hold 4,560 real supplement products containing Milk Thistle, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Milk Thistle. Your product may carry other ingredients that interact with Dronabinol too, on top of Milk Thistle — 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 Milk Thistle and Dronabinol 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 Milk Thistle
Top 5%

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

29 days ago today
Medication Dronabinol
Steady interest

#2,311 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 Milk Thistle

What is Milk Thistle?

Milk Thistle
  • Liver health and protection
  • Hepatitis
  • Cirrhosis
  • Gallbladder problems
  • High cholesterol
  • Type 2 diabetes support

Milk thistle is a popular herbal supplement most often used for liver health, and its main active component is a group of compounds called silymarin. While it is generally well tolerated, the scientific evidence that it meaningfully improves liver disease or other conditions is mixed and far from conclusive. Talk with your pharmacist or doctor before using it, especially if you have a liver condition or take other medicines.

Read the full Milk Thistle monograph & all interactions
Medication

About Dronabinol

What Is Dronabinol Used For?

Brand names: Marinol, Syndros

Dronabinol — available as capsules (Marinol, Dronabinol) and as an oral solution (Syndros, Dronabinol oral solution) — is approved for two conditions in adults. First, it treats anorexia (severely reduced appetite) associated with weight loss in patients with AIDS. Second, it controls nausea and vomiting caused by cancer chemotherapy in patients who have not gotten enough relief from standard anti-nausea treatments.

Both uses apply to all available formulations, but dosing timing and meal instructions differ between the capsule and oral solution products. Always follow the specific instructions for the product you have been prescribed.

See full Dronabinol drug information
Keep checking

Other Drugs & Milk Thistle

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

0Major
254Moderate
699Minor
1,876No known interaction
254 Moderate 699 Minor 1,876 No interaction
Moderate

254 interactions

Showing 60 of 254 moderate interactions — see all 254 on the Milk Thistle page.

Minor

699 interactions

Showing 60 of 699 minor interactions — see all 699 on the Milk Thistle page.

No interaction 1,876 drugs checked — show the list

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

Showing the 60 most looked-up of 1,876 medications checked with no known interaction — see the full Milk Thistle list.

See the full Milk Thistle interactions page
See every supplement checked against Dronabinol, 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
Milk Thistle monograph › Uses, safety, and every drug interaction in one place Dronabinol supplement interactions › Every supplement checked against Dronabinol, ranked by severity Dronabinol 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 Milk Thistle and Dronabinol Together: Common Questions

Can you take Milk Thistle with Dronabinol?
There is only a minor interaction, which is usually not serious. Read the full details on this page and confirm with your pharmacist before combining them.
Why are there 2 interactions listed for Milk Thistle and Dronabinol?
Dronabinol belongs to more than one drug category, and Milk Thistle 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 Milk Thistle and Dronabinol interaction?
We rate it Minor. This interaction is generally not clinically significant, but it remains worth noting and discussing with your pharmacist.

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

Still Have a Question About Dronabinol and Milk Thistle?

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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.