Cannabis and CBD: Medicine Interactions and Toxicology
How CBD and THC can interact with other medicines, what is known about liver effects and acute toxicity, and where the evidence is thin. For education, not advice.
Content last updated . This page has not been medically reviewed.
Urgent first
If someone may have swallowed too much cannabis, CBD or a hemp-derived product, or a child has eaten an edible, call US Poison Help at 1-800-222-1222 or the local poison center. For severe symptoms or immediate danger, call 911. [1] For other countries see poison help by country, and for first steps see poisoning: what to do first.How to read this page
This page is education only. It does not tell anyone to start, stop or change a medicine. Evidence labels used here: approved medicine (a regulator has approved a specific product), mixed, insufficient evidence, evidence of harm and preclinical (cells or animals only). Anyone who takes prescription medicines and uses cannabis products should talk with the prescriber or a pharmacist. For general background see how interactions work and interactions by drug class.Interactions
Why they can happen. The FDA says CBD can affect how other drugs work, and that studies of the approved CBD medicine show other medicines can change how much CBD is safe to take. [2] The two main cannabinoids, THC and CBD, are broken down by the same liver enzymes (CYP3A4, CYP2C9 and CYP2C19) that handle most prescription medicines. [3]How much is known. A 2023 review found CBD interactions reported for 53 of 403 drugs that those enzymes and transporters handle. In 31 of the 53, CBD raised the level of the other drug. The authors called for more studies. [4]
| Medicine or group | What the sources report | Evidence label |
|---|---|---|
| Warfarin (a blood thinner) | A systematic review found seven case reports; blood-clotting tests (INR) rose in six of seven. The review rated the data very low quality. [5] | Insufficient evidence, but a recognized signal |
| Valproate (a seizure medicine) | The approved CBD drug's label says using it with valproate at higher doses raises the risk of liver-enzyme elevations. [6] | Approved-drug label warning |
| Tacrolimus and sirolimus (transplant medicines) | A systematic review listed them with warfarin and valproate among the most widely reported cannabinoid interactions. [3] | Insufficient evidence |
| Alcohol and sedating medicines | The FDA says CBD with alcohol or other drugs that slow brain activity raises the risk of sedation and drowsiness, which can lead to injuries. [2] | Evidence of harm (additive sedation) |
| Other prescription medicines | The label lists several enzyme and transporter pathways where prescribers should consider adjusting other medicines. [6] | Approved-drug label warning |
The FDA adds that research on CBD combined with herbs and other plant products is limited. [2] The warfarin cases involved doses that were very high or not known, so they cannot be used to judge everyday products. [5]
Toxicology
Liver. The FDA found a risk of liver injury when reviewing the approved CBD medicine, and says it is unclear how this would be managed when CBD is used widely without supervision. [2] The label requires blood tests of liver enzymes before treatment. [6] In a small trial, 16 healthy adults took CBD for about 3.5 weeks at a study amount of 1,500 mg a day. Seven (44%) had liver enzyme (ALT) readings above normal, and five (31%) exceeded five times the upper limit, meeting the international criteria for drug-induced liver injury. All began within 2 to 4 weeks. [7] This is a study amount used to test safety, not a recommendation. See liver safety and supplements.Other CBD effects. The FDA lists sleepiness, diarrhea or lower appetite, and irritability or agitation, which should improve when CBD is stopped or reduced. [2] Damage to male reproductive organs was seen in animal studies, and it is not known whether this occurs in people (preclinical). [2]
THC and intoxicating products. NIDA says anxiety, fear, panic or hallucinations are more common after a large amount, a high-THC product or little experience. It also notes that intoxication can cause a temporary psychotic episode in some people, especially at high doses. [1] Eaten cannabis can take up to two hours to start working and up to four hours to reach full effect, according to Health Canada (an older page, so check the current one). [8] Long-term heavy use has been linked to cannabinoid hyperemesis syndrome (repeated nausea, vomiting and abdominal pain). [1]
Delta-8 THC. The FDA received 104 adverse event reports about delta-8 products over about 15 months, and poison centers logged 2,362 exposures in 14 months; 41% involved people under 18. [9] See THC for more.
Contaminants and label accuracy. The FDA tested some CBD products and many did not contain the CBD amount on the label, and it is investigating possible pesticides, heavy metals and THC. [2] NCCIH says over-the-counter CBD may contain more or less than labeled and may contain contaminants such as THC. [10] See certificates of analysis.
Where to go next
For the medicines that are approved, see approved cannabinoid medicines. For use disorder and other adverse effects, see cannabis adverse effects.Frequently asked questions
Does CBD interact with warfarin?
Case reports describe higher INR (a clotting measure) in people taking warfarin and a cannabinoid, but a systematic review rated the data very low quality. [5] Anyone on warfarin should tell the prescriber about any cannabis product.
Can CBD hurt the liver?
Yes, it can raise liver enzymes. The FDA names liver injury as a risk, and a small trial in healthy adults found enzyme rises in many participants at a high study amount. [2][7]
Is it safe to combine CBD with alcohol?
The FDA says the combination raises the risk of sedation and drowsiness, which can lead to injuries. [2]
Can you overdose on cannabis?
Too much THC can cause panic, hallucinations or a temporary psychotic episode, and children who eat edibles can become seriously ill. [1] Call Poison Help at 1-800-222-1222 for advice. [1]
Do herbal or "natural" CBD products avoid these risks?
No. The FDA says unapproved products have not been evaluated for dosage, interactions or side effects. [2]
References
- National Institute on Drug Abuse (NIH). Cannabis (Marijuana). Read 2026-10-22.
- U.S. Food and Drug Administration. What You Need to Know (And What We’re Working to Find Out) About Products Containing Cannabis or Cannabis-derived Compounds, Including CBD. Read 2026-10-22.
- Nachnani R, et al. Systematic review of drug-drug interactions of delta-9-tetrahydrocannabinol, cannabidiol, and Cannabis. Front Pharmacol 2024. PMID 38868665. Read 2026-10-22.
- Stöllberger C, Finsterer J. Cannabidiol's impact on drug-metabolization. Eur J Intern Med 2023. PMID 37541924. Read 2026-10-22.
- Smythe MA, Wu W, Garwood CL. Anticoagulant drug-drug interactions with cannabinoids: A systematic review. Pharmacotherapy 2023. PMID 37740600. Read 2026-10-22.
- DailyMed (U.S. National Library of Medicine). EPIDIOLEX (cannabidiol) oral solution, prescribing information, revised 5/2026. Read 2026-10-22.
- Watkins PB, et al. Cannabidiol and Abnormal Liver Chemistries in Healthy Adults: Results of a Phase I Clinical Trial. Clin Pharmacol Ther 2021. PMID 33022751. Read 2026-10-22.
- Health Canada. The Cannabis Act: Here’s what you need to know. Read 2026-10-22. Page text dates from about 2019 and may be out of date.
- U.S. Food and Drug Administration. 5 Things to Know about Delta-8 Tetrahydrocannabinol – Delta-8 THC. Read 2026-10-22.
- National Center for Complementary and Integrative Health (NIH). Cannabis (Marijuana) and Cannabinoids: What You Need To Know. Read 2026-10-22.