Drug & supplement interaction

Delta-9-tetrahydrocannabinol (thc) + Trandolapril, Verapamil

Trandolapril, Verapamil brand name: Tarka.

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

Trandolapril, Verapamil falls into 3 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
Interactions3
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Delta-9-tetrahydrocannabinol (thc) and Trandolapril, Verapamil

These two interact in 3 distinct ways. Each one is explained separately below.

Why Are There 3 Interactions?

Delta-9-tetrahydrocannabinol (thc) interacts with whole categories of medication. Trandolapril, Verapamil falls into 3 of those categories, so it can interact with Delta-9-tetrahydrocannabinol (thc) in 3 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 3

Why this applies to Trandolapril, Verapamil

Trandolapril, Verapamil 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 simple version: Tarka is a combo pill, and the verapamil part is a known blocker of a liver enzyme called CYP3A4. That same enzyme helps break down THC. So if you use THC while taking Tarka, the verapamil may slow how fast your body clears the THC, letting it build up a bit. In plain terms, your 'high' and side effects like drowsiness, dizziness, slowed thinking, or a faster or slower heartbeat could feel stronger or last longer than expected.

This is a theoretical concern based on how the drugs work, not strong real-world proof, so don't panic. Still, since verapamil also lowers blood pressure and heart rate, it's worth a quick chat with your pharmacist or doctor before combining 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

P-GLYCOPROTEIN SUBSTRATES

2 of 3

Trandolapril, Verapamil also falls under P-GLYCOPROTEIN SUBSTRATES.

Theoretically, THC might alter levels of drugs that are substrates of P-glycoprotein (P-gp).
Most in vitro research suggests that THC can inhibit P-gp and increase the accumulation of probe compounds by reducing P-gp mediated drug efflux. In vitro studies in kidney cell lines show that a 1-hour exposure to CBD and THC inhibits P-gp. THC may also alter the expression of P-gp, although this effect appears to vary based on duration of exposure. Some in vitro research in lymphoblastoid leukemia cell lines indicates that a 1-hour exposure to cannabinoids does not affect P-gp expression, while a prolonged 72-hour exposure decreases P-gp expression. Other in vitro research in these cell lines shows that a 4-hour exposure to THC and CBD induces P-gp gene expression, while exposure for longer than 4 hours and up to 48 hours does not induce P-gp gene expression.
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

Tarka combines two blood pressure medicines: trandolapril (an ACE inhibitor) and verapamil (a calcium channel blocker). The verapamil part travels through your body partly with the help of a pump called P-glycoprotein. Lab and animal studies hint that THC may slow this pump down, which could let a bit more verapamil hang around in your system. If that happens, you might notice more of verapamil's usual effects, like dizziness, a slower heart rate, low blood pressure, fatigue, or constipation.

I want to be honest with you though: this is only theoretical, based on test-tube and animal work, not real patients. So it may not matter much in practice. Still, since blood pressure and heart rate are worth watching, let your pharmacist or doctor know if you use THC so they can keep an eye on things.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Zhu, H. J., Wang, J. S., Markowitz, J. S., Donovan, J. L., Gibson, B. B., Gefroh, H. A., and Devane, C. L. Characterization of P-glycoprotein inhibition by major cannabinoids from marijuana. J Pharmacol Exp.Ther. 2006;317(2):850-857. PubMed
  2. Holland, M. L., Panetta, J. A., Hoskins, J. M., Bebawy, M., Roufogalis, B. D., Allen, J. D., and Arnold, J. C. The effects of cannabinoids on P-glycoprotein transport and expression in multidrug resistant cells. Biochem.Pharmacol 4-14-2006;71(8):1146-115 PubMed
  3. Tournier N, Lucie Chevillard L, Megarbane B, et al. Interaction of drugs of abuse and maintenance treatments with human P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2). Int J Neuropsychopharmacol. 2010;13(7):905-15. PubMed
  4. Arnold JC, Hone P, Holland ML, Allen JD. CB2 and TRPV1 receptors mediate cannabinoid actions on MDR1 expression in multidrug resistant cells. Pharmacol Rep. 2012;64(3):751-7. PubMed
Minor

CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES

3 of 3

Trandolapril, Verapamil also falls under CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES.

Theoretically, THC may increase the levels and clinical effects of CYP3A4 substrates.
In vitro research shows that cannabis containing THC might modestly inhibit the activity of CYP3A4 enzymes, which might decrease the metabolism of CYP3A4 substrates. It is unclear if this effect is due to THC, other constituents, or the combination. In vitro research also shows that cannabis extracts containing THC modestly inhibit the CYP3A4 metabolism of testosterone; extracts providing the specific cannabinoids cannabidiol (CBD) or cannabigerol (CBG) alone had stronger inhibitory effects than extracts containing both THC and CBD. Conversely, a crossover clinical study in healthy adults shows that oral THC does not inhibit CYP3A4.
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 gist with Tarka (which combines trandolapril, an ACE inhibitor, with verapamil, a calcium channel blocker). Verapamil is partly cleared by a liver enzyme called CYP3A4. In lab dish studies, THC seemed to mildly slow that same enzyme. In theory, that could let verapamil build up a little, which might mean lower blood pressure, a slower heart rate, dizziness, swollen ankles, or constipation.

I want to keep this in perspective, though. This is only test-tube data, and a human study using oral THC actually found no meaningful effect on CYP3A4. So a real-world problem here is unlikely. Still, since blood pressure and heart rate are nothing to gamble with, mention any cannabis use to your pharmacist or doctor before combining them.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Pellinen, P., Honkakoski, P., Stenback, F., Niemitz, M., Alhava, E., Pelkonen, O., Lang, M. A., and Pasanen, M. Cocaine N-demethylation and the metabolism-related hepatotoxicity can be prevented by cytochrome P450 3A inhibitors. Eur.J Pharmacol 1-3-1994;2 PubMed
  2. Treyer A, Reinhardt JK, Eigenmann DE, Oufir M, Hamburger M. Phytochemical comparison of medicinal cannabis extracts and study of their CYP-mediated interactions with coumarinic oral anticoagulants. Med Cannabis Cannabinoids. 2023;6(1):21-31. PubMed
  3. Bansal S, Zamarripa CA, Spindle TR, et al. Evaluation of Cytochrome P450-Mediated Cannabinoid-Drug Interactions in Healthy Adult Participants. Clin Pharmacol Ther 2023.

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 762 moderate, 336 minor known drug interactions in our database — the Trandolapril, Verapamil one above is among them. If you take anything else, check it against the full list below.

Moderate 762 Minor 336 No known interaction 1,732 (incl. Trandolapril, Verapamil)
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.

Everything else you take

See Every Supplement That Interacts With Trandolapril, Verapamil

This page covers Delta-9-tetrahydrocannabinol (thc) only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Trandolapril, Verapamil page lists 304 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), American Hellebore (major), American Mistletoe (major), Asarabacca (major) and Beer (major).

By severity: 11 major · 250 moderate · 43 minor.

From our pharmacist’s overview on the Trandolapril, Verapamil page

“This is one of the supplement lists I would want a patient to read closely, not skim. Tarka combines trandolapril and verapamil to lower blood pressure, and most of these interactions pull on that same lever, either dropping pressure further than intended or working against the medicine altogether.”

Reviewed by 2 · Jul 18, 2026

Open the Trandolapril, Verapamil interaction page

How much people look this up

Where Delta-9-tetrahydrocannabinol (thc) and Trandolapril, Verapamil 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

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

29 days ago today
Medication Trandolapril, Verapamil
Top 25%

#446 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
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
762Moderate
336Minor
1,731No known interaction
762 Moderate 336 Minor 1,731 No interaction
Moderate

762 interactions

Showing 60 of 762 moderate interactions — see all 762 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 1,731 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 1,731 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 Trandolapril, Verapamil, 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 Trandolapril, Verapamil supplement interactions › Every supplement checked against Trandolapril, Verapamil, 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 Delta-9-tetrahydrocannabinol (thc) and Trandolapril, Verapamil Together: Common Questions

Can you take Delta-9-tetrahydrocannabinol (thc) with Trandolapril, Verapamil?
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 3 interactions listed for Delta-9-tetrahydrocannabinol (thc) and Trandolapril, Verapamil?
Trandolapril, Verapamil 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 Trandolapril, Verapamil 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

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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.