Drug & supplement interaction

Delta-9-tetrahydrocannabinol (thc) + Thiopental

Thiopental brand name: Pentothal.

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

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

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 Thiopental

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. Thiopental 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

BARBITURATES

1 of 2

Why this applies to Thiopental

Thiopental falls under BARBITURATES — the group Delta-9-tetrahydrocannabinol (thc) interacts with.

Theoretically, THC might increase the levels and adverse effects of barbiturates.
Some research shows that synthetic THC (dronabinol) increases the elimination half-life of pentobarbital by 4 hours when dosed concomitantly. Also, in animal research, THC potentiated pentobarbital-induced sleep by more than three-fold.
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 it. Thiopental (Pentothal) is a fast-acting barbiturate used mainly to put people to sleep before surgery or to calm severe seizures. It's a powerful brain depressant, not a prodrug, so it doesn't need activating. The concern with THC is that it may slow how quickly your body clears barbiturates, letting the drug linger and hit harder. In animal studies, THC more than tripled barbiturate-induced sleep, and a related synthetic THC lengthened a similar drug's half-life by about 4 hours.

In real terms, that could mean deeper, longer sedation, slowed breathing, very low blood pressure, and a groggier recovery. Keep in mind this is mostly lab and animal evidence, so it's theoretical in people. Still, since thiopental is given in tightly controlled settings, always tell your anesthesia team and pharmacist about any cannabis or THC use beforehand.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Marinol Prescribing Information. Solvay Pharmaceuticals, Rev March 2008. Available at: http://www.solvaypharmaceuticals-us.com/static/wma/pdf/1/3/2/5/0/004InsertText500012RevMar2008.pdf (Accessed 2 July 2009).
  2. Kimura T, Takaya M, Usami N, Watanabe K, Yamamoto I. ?9-Tetrahydrocannabinol, a major marijuana component, enhances the anesthetic effect of pentobarbital through the CB1 receptor. Forensic Toxicol. 2019;37(1):207-214. DOI
Moderate

ANESTHESIA

2 of 2

Thiopental also falls under ANESTHESIA.

THC use might alter the safety and clinical effects of various forms of anesthesia.
Cannabis contains THC. A small clinical study shows that higher doses of propofol may be needed to achieve relaxation and loss of consciousness in chronic cannabis users compared with nonusers. Another small clinical study shows that use of cannabis within 72 hours prior to undergoing surgery requiring atropine anesthesia may increase the risk of sustained postoperative tachycardia. The exact mechanisms of these interactions are unclear. Obtain a patient's history of cannabis use preoperatively and advise patients to discontinue use for at least 2 weeks prior to undergoing surgery.
Severity Moderate Likelihood Possible Evidence B

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

Thiopental (Pentothal) is a fast-acting barbiturate that anesthesiologists use to put people under. Here's the practical concern: people who use cannabis regularly may need more anesthetic medication to reach the same level of sedation. The clinical signal we have is strongest for propofol, but it's reasonable to think a similar pattern could apply to other agents used during anesthesia, including thiopental. THC isn't a prodrug issue here, the worry is simply that chronic use may blunt how well sedation works and could affect things like heart rate.

This is based on small studies, so it's a possible rather than certain interaction. Still, it genuinely matters in the operating room. Always tell your surgical team and anesthesiologist about any cannabis or THC use beforehand, and follow their guidance on stopping before surgery.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Huson HB, Granados TM, Rasko Y. Surgical considerations of marijuana use in elective procedures. Heliyon. 2018;4(9):e00779. PubMed
  2. Goyal H, Awad HH, Ghali JK. Role of cannabis in cardiovascular disorders. J Thorac Dis. 2017;9(7):2079-2092. 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

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 Thiopental 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. Thiopental)
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 Thiopental

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

The most serious there right now: Fever Bark (major), Adrue (moderate), Cannabis (moderate), Cowhage (moderate) and Datura Wrightii (moderate).

By severity: 1 major · 7 moderate · 1 minor.

From our pharmacist’s overview on the Thiopental page

“If a procedure is on your calendar and thiopental (Pentothal) is the drug that will put you under, the nine supplements listed here deserve genuine attention before anyone reaches for the syringe. One of them, fever bark, carries the lone major rating because a compound in it, reserpine, has been linked to unstable blood pressure and h…”

Reviewed by 2 · Jul 18, 2026

Open the Thiopental interaction page

How much people look this up

Where Delta-9-tetrahydrocannabinol (thc) and Thiopental 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

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

29 days ago today
Medication Thiopental
Steady interest

#2,664 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
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 Thiopental, 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 Thiopental supplement interactions › Every supplement checked against Thiopental, 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 Thiopental Together: Common Questions

Can you take Delta-9-tetrahydrocannabinol (thc) with Thiopental?
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 Thiopental?
Thiopental 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 Thiopental 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.