Drug & supplement interaction

Cannabis + Belladonna, Ergotamine, Phenobarbital

Belladonna, Ergotamine, Phenobarbital brand name: Bellergal-S.

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

Belladonna, Ergotamine, Phenobarbital falls into 5 drug categories that Cannabis can interact with; the most serious is rated moderate. Theoretically, cannabis might have additive effects if used with other CNS depressants.

Read the full interaction report
SeverityModerate
LikelihoodPossible
Interactions5
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Cannabis and Belladonna, Ergotamine, Phenobarbital

These two interact in 5 distinct ways. Each one is explained separately below.

Why Are There 5 Interactions?

Cannabis interacts with whole categories of medication. Belladonna, Ergotamine, Phenobarbital falls into 5 of those categories, so it can interact with Cannabis in 5 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Moderate).

Moderate

CNS DEPRESSANTS

1 of 5

Why this applies to Belladonna, Ergotamine, Phenobarbital

Belladonna, Ergotamine, Phenobarbital falls under CNS DEPRESSANTS — the group Cannabis interacts with.

Theoretically, cannabis might have additive effects if used with other CNS depressants.
Cannabis can have CNS depressant effects. Combining cannabis with other CNS depressants might result in additive or synergistic effects. A small clinical trial in healthy adults shows that inhaling a high-grade cannabis (Bedrocan International B.V., Veendam, The Netherlands) 100 mg, containing delta-9-tetrahydrocannabinol 21.8% and cannabinol 0.1%, modestly increases subjective feelings of sedation when compared with cannabis alone.
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

The piece of Bellergal-S that matters most here is the phenobarbital, a barbiturate that calms the brain. Cannabis (especially THC) can also slow down the central nervous system, so using the two together may stack those effects. You could feel more drowsy, foggy, or dizzy than you'd expect, with slower reactions and weaker coordination. That's worth respecting since this combination already includes a sedating drug.

To be fair, this concern is mostly theoretical, based on how these substances act rather than hard outcome studies, and one small trial only showed a modest bump in sedation. Still, I'd avoid driving or anything risky until you know how you react, and check with your doctor or pharmacist before combining them.

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. Hollister, L. E. Interactions of cannabis with other drugs in man. NIDA Res.Monogr 1986;68:110-116. DOI
  3. van Dam CJ, van der Schrier R, van Velzen M, et al. Inhaled Delta(9)-tetrahydrocannabinol does not enhance oxycodone-induced respiratory depression: randomised controlled trial in healthy volunteers. Br J Anaesth 2023;130(4):485-493.
Moderate

CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES

2 of 5

Belladonna, Ergotamine, Phenobarbital also falls under CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES.

Theoretically, cannabis may increase the levels and adverse effects of CYP3A4 substrates.
In vitro research shows that cannabis can inhibit the activity of CYP3A4 enzymes, which might decrease the metabolism of CYP3A4 substrates. In vitro research also shows that cannabis extracts modestly inhibit the CYP3A4 metabolism of testosterone; extracts providing the specific cannabinoids CBD and cannabigerol (CBG) had stronger inhibitory effects than extracts containing THC and CBD.
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

This combination pill (Bellergal-S) mixes three things: belladonna, ergotamine, and the barbiturate phenobarbital. The concern here is mostly about ergotamine, which your liver clears using an enzyme called CYP3A4. Lab studies suggest cannabis can slow that enzyme down a bit, which could let ergotamine build up more than expected. With ergotamine, higher levels can mean stronger side effects like nausea, tingling or coldness in your fingers and toes, and tightening of blood vessels.

I want to keep this in perspective, though. This is theoretical and based only on test-tube research, not real patients, so the actual risk is uncertain. Still, since this is an older, sensitive medication, it's worth a quick chat with your pharmacist or doctor before combining the two.

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
Moderate

BARBITURATES

3 of 5

Belladonna, Ergotamine, Phenobarbital also falls under BARBITURATES.

Theoretically, cannabis might increase the levels and adverse effects of barbiturates.
Some research shows that synthetic delta-9-tetrahydrocannabinol (THC) increases the elimination half-life of pentobarbital by 4 hours when dosed concomitantly.
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

The piece of Bellergal-S we care about here is the phenobarbital, a barbiturate. The thinking is that cannabis (especially THC) may slow how fast your body clears phenobarbital, so it can linger a bit longer. In one study, THC stretched the half-life of a similar barbiturate by about 4 hours. If that happens, you could feel more of phenobarbital's usual effects: extra drowsiness, grogginess, dizziness, slowed breathing, or feeling foggy and unsteady on your feet.

This is mostly theory based on how the drugs behave, not strong human proof, so don't panic. Still, both can be sedating on their own, so the combo deserves caution. Please check with your pharmacist or doctor before mixing them, and never stop or change either one on your own.

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).
Moderate

CYTOCHROME P450 3A4 (CYP3A4) INDUCERS

4 of 5

Belladonna, Ergotamine, Phenobarbital also falls under CYTOCHROME P450 3A4 (CYP3A4) INDUCERS.

Theoretically, CYP3A4 inducers might reduce the levels and clinical effects of cannabis.
Delta-9-tetrahydrocannabinol (THC), an active constituent of cannabis, 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 thing with this combo product (Bellergal-S): it contains phenobarbital, a barbiturate that revs up a liver enzyme called CYP3A4. Your body uses that same enzyme to break down THC, the main active compound in cannabis. So when phenobarbital speeds up that enzyme, it can clear THC out of your system faster. In plain terms, your cannabis may feel weaker or shorter-lasting than you expect.

I'll be honest, this is a theoretical concern based on how the drugs work, not something proven in studies, so don't panic. The bigger real-world worry is the other direction: cannabis and phenobarbital can both cause drowsiness and dizziness, so together you may feel extra sleepy or unsteady. Please check 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

CYTOCHROME P450 2C9 (CYP2C9) INDUCERS

5 of 5

Belladonna, Ergotamine, Phenobarbital also falls under CYTOCHROME P450 2C9 (CYP2C9) INDUCERS.

Theoretically, drugs that are CYP2C9 inducers might decrease the effects of cannabis.
Delta-9-tetrahydrocannabinol (THC), an active constituent of cannabis, 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 thing to know about this combo: it's the cannabis side that may be affected, not your Bellergal-S. The phenobarbital in this product is a known liver enzyme booster, including the CYP2C9 pathway that helps break down THC. So in theory, taking it regularly could clear THC faster and leave cannabis feeling weaker or shorter-lasting than you'd expect.

I'll be honest, this one is based on how the drugs work on paper, not on solid studies, so I wouldn't lose sleep over it. Your Bellergal-S should still do its job for headaches or related symptoms. Just keep in mind the sedation from phenobarbital plus cannabis can stack up and make you very drowsy. Please run your full routine by your pharmacist or doctor first.

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

Cannabis Also Interacts With Other Medications

Cannabis has 2 major, 1,108 moderate, 25 minor known drug interactions in our database — the Belladonna, Ergotamine, Phenobarbital one above is among them. If you take anything else, check it against the full list below.

Major 2 Moderate 1,108 Minor 25 No known interaction 1,695 (incl. Belladonna, Ergotamine, Phenobarbital)
Taking anything else?

Check Another of Your Medications Against Cannabis

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

From our Q&A

Questions About Cannabis or Belladonna, Ergotamine, Phenobarbital

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Cannabis or Belladonna, Ergotamine, Phenobarbital, 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 Belladonna, Ergotamine, Phenobarbital

This page covers Cannabis only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Belladonna, Ergotamine, Phenobarbital page lists 250 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: 1,4-butanediol (major), Activated Charcoal (major), Beer (major), Gamma-hydroxybutyrate (ghb) (major) and Grapefruit (major).

By severity: 11 major · 200 moderate · 39 minor.

From our pharmacist’s overview on the Belladonna, Ergotamine, Phenobarbital page

“Bellergal-S packs three drugs into one tablet, and its supplement list earns real respect before you mix in anything else. Phenobarbital is a sedating barbiturate, belladonna adds drying anticholinergic effects, and ergotamine constricts blood vessels, so this combination collects interactions from several directions at once.”

Reviewed by 2 · Jul 18, 2026

Open the Belladonna, Ergotamine, Phenobarbital interaction page

One more smart check

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

We hold 21 real supplement products containing Cannabis, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Cannabis. Your product may carry other ingredients that interact with Belladonna, Ergotamine, Phenobarbital too, on top of Cannabis — 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 Cannabis and Belladonna, Ergotamine, Phenobarbital 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 Cannabis
Top 25%

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

29 days ago today
Medication Belladonna, Ergotamine, Phenobarbital
Top 5%

#93 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 Cannabis

What is Cannabis?

Cannabis
  • Chronic pain
  • Nausea and vomiting from chemotherapy
  • Muscle spasticity (e.g., multiple sclerosis)
  • Anxiety and stress
  • Sleep problems
  • Appetite stimulation

Cannabis contains many active compounds, mainly THC (which causes a 'high') and CBD (which does not). Some uses, such as chemotherapy-related nausea, certain seizure disorders, and muscle spasticity, have meaningful evidence, while many other popular uses are not well proven. It can cause real side effects and impairment, so talk to your doctor or pharmacist and follow your local laws before using it.

Read the full Cannabis monograph & all interactions
Keep checking

Other Drugs & Cannabis

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

2Major
1,108Moderate
25Minor
1,694No known interaction
2 Major 1,108 Moderate 25 Minor 1,694 No interaction
Major

2 interactions

Moderate

1,108 interactions

Showing 60 of 1,108 moderate interactions — see all 1,108 on the Cannabis page.

Minor

25 interactions

No interaction 1,694 drugs checked — show the list

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

Showing the 60 most looked-up of 1,694 medications checked with no known interaction — see the full Cannabis list.

See the full Cannabis interactions page
See every supplement checked against Belladonna, Ergotamine, Phenobarbital, 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
Cannabis monograph › Uses, safety, and every drug interaction in one place Belladonna, Ergotamine, Phenobarbital supplement interactions › Every supplement checked against Belladonna, Ergotamine, Phenobarbital, 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 Cannabis and Belladonna, Ergotamine, Phenobarbital Together: Common Questions

Can you take Cannabis with Belladonna, Ergotamine, Phenobarbital?
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 5 interactions listed for Cannabis and Belladonna, Ergotamine, Phenobarbital?
Belladonna, Ergotamine, Phenobarbital belongs to more than one drug category, and Cannabis 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 Cannabis and Belladonna, Ergotamine, Phenobarbital 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.