Drug & supplement interaction

Delta-9-tetrahydrocannabinol (thc) + Metronidazole

Metronidazole brand names: Flagyl, Protostat, Metronidazole, Nidazol, Trikacide, and others.

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

Metronidazole falls into 2 drug categories that Delta-9-tetrahydrocannabinol (thc) can interact with; the most serious is rated moderate. Theoretically, CYP3A4 inhibitors might increase the levels and clinical effects of THC.

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

Delta-9-tetrahydrocannabinol (thc) and Metronidazole

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

Why Are There 2 Interactions?

Delta-9-tetrahydrocannabinol (thc) interacts with whole categories of medication. Metronidazole falls into 2 of those categories, so it can interact with Delta-9-tetrahydrocannabinol (thc) in 2 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Moderate).

Moderate

CYTOCHROME P450 3A4 (CYP3A4) INHIBITORS

1 of 2

Why this applies to Metronidazole

Metronidazole falls under CYTOCHROME P450 3A4 (CYP3A4) INHIBITORS — the group Delta-9-tetrahydrocannabinol (thc) interacts with.

Theoretically, CYP3A4 inhibitors might increase the levels and clinical effects of THC.
THC is a substrate of CYP3A4 enzymes.
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 gist for this pairing: your body uses an enzyme called CYP3A4 to help break down THC. Metronidazole (Flagyl) can mildly block that enzyme, so in theory THC may hang around a bit longer and feel stronger. That could mean more pronounced effects like feeling extra high, dizzy, drowsy, or foggy-headed.

I want to keep this in perspective, though. This concern is theoretical, based on how the drugs work on paper rather than real patient reports, so it may not amount to much for most people. Metronidazole itself doesn't mix well with alcohol, and combining it with cannabis could add to nausea or lightheadedness. Please run your situation by your pharmacist or doctor before pairing them.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Product information for Marinol. AbbVie. North Chicago, IL 60064. August 2017. Available at: https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/018651s029lbl.pdf.
Moderate

CYTOCHROME P450 2C9 (CYP2C9) INHIBITORS

2 of 2

Metronidazole also falls under CYTOCHROME P450 2C9 (CYP2C9) INHIBITORS.

Theoretically, drugs that are CYP2C9 inhibitors might increase the levels and adverse effects of THC.
THC is a substrate of CYP2C9 enzymes.
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 gist of this pairing. Your body uses an enzyme called CYP2C9 to help break down THC. Metronidazole can slow that enzyme down a bit, so in theory THC may not clear as quickly and could build up. That might mean a stronger or longer-lasting high, plus more of THC's usual effects like drowsiness, dizziness, a racing heart, or feeling foggy and off-balance.

I want to be honest about the strength of this one: it's theoretical, based on how these substances work on paper, not on solid human studies. For most people it's likely minor. Metronidazole itself doesn't mix well with alcohol, so go easy there too. If you use cannabis regularly, just give your pharmacist or doctor a heads-up so they can weigh in for your situation.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Product information for Marinol. AbbVie. North Chicago, IL 60064. August 2017. Available at: https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/018651s029lbl.pdf.

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

Delta-9-tetrahydrocannabinol (thc) Also Interacts With Other Medications

Delta-9-tetrahydrocannabinol (thc) has 761 moderate, 336 minor known drug interactions in our database — the Metronidazole one above is among them. If you take anything else, check it against the full list below.

Moderate 761 Minor 336 No known interaction 1,733 (incl. Metronidazole)
Taking anything else?

Check Another of Your Medications Against Delta-9-tetrahydrocannabinol (thc)

Covers the 2,830 medications we’ve checked against Delta-9-tetrahydrocannabinol (thc). Pick one to open its full report.

From our Q&A

Questions About Delta-9-tetrahydrocannabinol (thc) or Metronidazole

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Delta-9-tetrahydrocannabinol (thc) or Metronidazole, 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 Metronidazole

This page covers Delta-9-tetrahydrocannabinol (thc) only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Metronidazole page lists 83 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), American Hellebore (major), Arsenic (major), Cesium (major) and Ephedra (major).

By severity: 7 major · 63 moderate · 13 minor.

From our pharmacist’s overview on the Metronidazole page

“Metronidazole (Flagyl) can stretch the heart's QT interval on its own, and most of the seven major-rated interactions among its 83 flagged supplement ingredients do the same thing, so I read this list with more wariness than most antibiotics earn. Grapefruit and ephedra stand out for adding to that heart-rhythm risk, while activated ch…”

Reviewed by 2 · Jul 18, 2026

Open the Metronidazole interaction page

How much people look this up

Where Delta-9-tetrahydrocannabinol (thc) and Metronidazole 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 Delta-9-tetrahydrocannabinol (thc)
Top half

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

29 days ago today
Medication Metronidazole
Top half

#801 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 Delta-9-tetrahydrocannabinol (thc)

What is Delta-9-tetrahydrocannabinol (thc)?

Delta-9-tetrahydrocannabinol (thc)
  • Chronic or nerve pain
  • Nausea and vomiting from chemotherapy
  • Appetite loss and weight loss
  • Muscle spasticity
  • Sleep problems
  • Anxiety and stress

THC is the main mind-altering compound in cannabis and is best known for causing a 'high.' A prescription form (dronabinol) is approved for chemotherapy-related nausea and appetite loss, but for most other uses the evidence is mixed or limited, and THC can impair thinking and driving. It should be avoided in pregnancy and breastfeeding and used only with medical guidance.

Read the full Delta-9-tetrahydrocannabinol (thc) monograph & all interactions
Medication

About Metronidazole

What Is Metronidazole Used For?

Brand names: Flagyl, Protostat, Metronidazole, Nidazol, Trikacide, MetroGel, Flagyl IV, Metronidazole Redi-Infusion, Flagyl IV RTU, Metro IV, Anabact, Metrosa, Metrotop, Noritate, Rozex Cream, Rozex Gel, Zyomet, Likmez

Metronidazole treats three main types of infections. It's used for trichomoniasis (a sexually transmitted parasitic infection), amebiasis (an intestinal or liver infection caused by a parasite), and serious anaerobic bacterial infections — infections caused by bacteria that thrive without oxygen, which can affect the abdomen, skin, bones, lungs, and other areas.

Because sexual partners can pass trichomoniasis back and forth, both partners are typically treated at the same time, even if one has no symptoms.

See full Metronidazole drug information
Keep checking

Other Drugs & Delta-9-tetrahydrocannabinol (thc)

Browse every other medication we’ve checked against Delta-9-tetrahydrocannabinol (thc) — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
761Moderate
336Minor
1,732No known interaction
761 Moderate 336 Minor 1,732 No interaction
Moderate

761 interactions

Showing 60 of 761 moderate interactions — see all 761 on the Delta-9-tetrahydrocannabinol (thc) page.

Minor

336 interactions

Showing 60 of 336 minor interactions — see all 336 on the Delta-9-tetrahydrocannabinol (thc) page.

No interaction 1,732 drugs checked — show the list

We also checked Delta-9-tetrahydrocannabinol (thc) against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 1,732 medications checked with no known interaction — see the full Delta-9-tetrahydrocannabinol (thc) list.

See the full Delta-9-tetrahydrocannabinol (thc) interactions page
See every supplement checked against Metronidazole, 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
Delta-9-tetrahydrocannabinol (thc) monograph › Uses, safety, and every drug interaction in one place Metronidazole supplement interactions › Every supplement checked against Metronidazole, ranked by severity Metronidazole 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 Delta-9-tetrahydrocannabinol (thc) and Metronidazole Together: Common Questions

Can you take Delta-9-tetrahydrocannabinol (thc) with Metronidazole?
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 Delta-9-tetrahydrocannabinol (thc) and Metronidazole?
Metronidazole belongs to more than one drug category, and Delta-9-tetrahydrocannabinol (thc) 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 Delta-9-tetrahydrocannabinol (thc) and Metronidazole 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 Metronidazole and Delta-9-tetrahydrocannabinol (thc)?

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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.