Last updated: October 2026
Yes, CBD can interact with some medicines, though fewer than older warnings suggest. The clearest interactions in people are with the epilepsy medicines clobazam and valproate, the transplant medicines tacrolimus and everolimus, and warfarin, mostly at prescription doses. The FSA advises anyone taking medication not to use CBD unless a doctor agrees, so ask your GP or pharmacist first.
Below: how interactions work, what the grapefruit warning does and doesn’t tell you, a table of medicine groups, why dose matters and how to use CBD more safely. This is general information, not medical advice.
How CBD interacts with medicines
CBD is broken down mainly in the liver. The UK product information for Epidyolex, the licensed prescription CBD medicine (see prescription CBD vs over-the-counter CBD), names CYP2C19 and CYP3A4 as the main enzymes that process it, with a second set of enzymes called UGTs finishing the job. That creates three kinds of interaction.
- CBD changing your medicine. In people, CBD raised the active breakdown product of clobazam three to four-fold, most likely by slowing CYP2C19. It raised everolimus about 2.5-fold, which the product information puts down to CBD blocking a pump in the gut wall called P-gp. It also nearly doubled total exposure to caffeine, a sign it weakly slows CYP1A2 (see CBD and coffee). Lab tests suggest it can also slow CYP2C9, CYP2C8, CYP2B6 and some UGTs, which could affect medicines such as warfarin, phenytoin and lamotrigine.
- Your medicine changing CBD. The antibiotic rifampicin, which speeds up CYP3A4 and CYP2C19, cut CBD levels by about 30% and its active breakdown product by about 60%. The product information says carbamazepine and St John’s wort may do the same. See CBD and antibiotics.
- Effects adding together. CBD can cause drowsiness, and the product information warns that other sedating medicines and alcohol can add to it. Liver enzyme rises are more common when CBD is taken with valproate than with CBD alone.
Does CBD block CYP3A4?
Not much, on current evidence in people. The common claim that CBD “blocks CYP3A4”, and so raises levels of a huge range of medicines, came mainly from lab studies and early reviews.
When researchers tested it properly, giving healthy volunteers about 1,500mg of CBD a day for two weeks, CBD made no difference to midazolam, the standard test medicine used to measure CYP3A4 activity. The UK Epidyolex product information, updated in June 2026, now says CBD did not inhibit or induce CYP3A4 in that study. Blocking CYP3A4 with the antifungal itraconazole also had no relevant effect on CBD levels, while the antifungal fluconazole, which blocks CYP2C19, raised them slightly.
That doesn’t make CBD interaction-free. Its better-documented effects run through CYP2C19, the gut pump P-gp, the liver and drowsiness, and a recent trial found CBD raised tacrolimus levels about three-fold for reasons still unclear. So check any regular medicine, whatever enzyme it uses.
The grapefruit warning: a prompt, not a rule
Some medicine leaflets tell you to avoid grapefruit or grapefruit juice. That’s because grapefruit blocks CYP3A4 in the small intestine, so more of the medicine reaches the blood. Medicines with this warning include some statins, nifedipine, ciclosporin, amiodarone and buspirone.
Many websites say CBD works like grapefruit, so a grapefruit warning means CBD will raise your medicine too. That’s an oversimplification. CBD didn’t affect CYP3A4 in the midazolam study, and its best-known interactions mostly run through other routes: CYP2C19 for clobazam, an unknown mechanism for valproate, and probably CYP2C9 for warfarin.
The warning is still a useful prompt for one reason: grapefruit-warning medicines include the transplant medicine ciclosporin, and transplant medicines are exactly the group where CBD has raised levels in people (tacrolimus and everolimus). So:
- Grapefruit warning on your medicine? Ask your pharmacist before using CBD.
- No grapefruit warning? That doesn’t mean it’s safe to combine. The clobazam interaction, for example, runs through CYP2C19, not CYP3A4.
Medicines to check before using CBD
Strength of evidence: strong means measured in studies in people; moderate means case reports or small studies; limited means lab data or prediction only.
| Medicine group | What’s known | Strength of evidence | What to do |
|---|---|---|---|
| Epilepsy medicines: clobazam, valproate, stiripentol, phenytoin, lamotrigine | Clobazam’s active breakdown product rises three to four-fold, with more drowsiness. Liver enzyme rises are more common with valproate. Stiripentol rose slightly; phenytoin and lamotrigine may rise | Strong for clobazam, valproate and stiripentol; limited for phenytoin and lamotrigine | Don’t add CBD without your epilepsy team. Never stop or change an epilepsy medicine yourself |
| Transplant and immune medicines: tacrolimus, everolimus, sirolimus, ciclosporin | CBD raised everolimus about 2.5-fold and tacrolimus about three-fold in healthy volunteers. Sirolimus may rise too. We found no study of CBD with ciclosporin | Strong for everolimus; moderate for tacrolimus (one small trial); limited for the others | Avoid CBD unless your transplant or specialist team agrees and monitors your levels |
| Warfarin | INR rose as prescription CBD was increased in case reports, and warfarin was cut by about 20% to 30%. A 2023 review rated this very low-quality evidence, with almost none for other anticoagulants | Moderate (case reports at high CBD doses) | Tell your anticoagulation clinic before starting and expect extra INR checks |
| Sedatives, sleeping tablets and strong painkillers, and alcohol | Drowsiness adds up. CBD didn’t change midazolam levels, but lab data predict rises in lorazepam and morphine | Strong for added drowsiness; limited for level changes | Ask a pharmacist. Don’t drive if drowsy, and go easy on alcohol |
| Digoxin and other medicines carried by P-gp | Levels may rise, by the same gut route as everolimus | Limited (prediction) | Ask your GP before using CBD |
| Other medicines processed by CYP2C19, CYP2C8 or CYP1A2: omeprazole, repaglinide (diabetes), theophylline, tizanidine | Levels may rise. Caffeine exposure nearly doubled with high-dose CBD | Limited, except caffeine (strong) | Ask a pharmacist, and cut back on caffeine if you feel jittery |
| Medicines that lower CBD: rifampicin, carbamazepine, St John’s wort, enzalutamide | CBD levels fall by about 30% with rifampicin; the others may act similarly | Strong for rifampicin | Unlikely to be harmful, but CBD may do less. Tell your prescriber |
| Blood pressure and heart medicines, statins | A single large CBD dose lowered resting blood pressure slightly in healthy men. Statins and calcium channel blockers with grapefruit warnings rely on CYP3A4, which CBD didn’t affect in the midazolam study, but we found no studies of them with CBD | Limited | Ask a pharmacist, and check your blood pressure if you feel dizzy |
| Antidepressants | Little direct research. Lab data predict an interaction with bupropion, in either direction; drowsiness can add up | Limited | Speak to your GP or pharmacist first, and never stop an antidepressant suddenly |
| Thyroid medicines | We found no studies of CBD with levothyroxine. In a 2025 trial in healthy adults, four weeks of CBD didn’t change thyroid hormone levels | Limited | Ask a pharmacist, and keep your CBD amount steady before thyroid blood tests |
This isn’t a complete list. Always check your specific medicine with a pharmacist. Planning an operation? Read CBD before surgery.
Does the amount of CBD matter?
Yes, a lot. The interaction studies above mostly used prescription doses: 1,500mg a day in the midazolam and caffeine studies, and roughly 700mg a day for an average adult in the tacrolimus trial. Where the dose was known, the warfarin case reports involved more than 600mg a day. That is 60 to 150 times the FSA’s 10mg a day.
A 2023 review in the German medical journal Deutsches Ärzteblatt concluded that clinically relevant CBD interactions are likely only above about 300mg a day. But supplement amounts haven’t been tested directly, so caution still applies for the higher-risk medicines in the table, especially warfarin, epilepsy and transplant medicines. See our guide to the FSA’s 10mg advice.
Two everyday things change how much CBD you absorb. Taken with a high-fat meal, CBD absorption rose about four-fold in studies; with alcohol it rose by 63%. So take CBD the same way each day, rather than switching between an empty stomach and a big meal (see CBD and alcohol).
The FSA’s 10mg a day figure is precautionary advice rather than a legal limit, set while longer-term safety research continues. At Evopure we think it is a very cautious figure, and many adults use more. If you go above it, increase slowly, and check with your GP or pharmacist first if you take any medication.
CBD, your liver and other medicines
At high doses, CBD can raise liver enzyme levels in blood tests. In a 2021 trial, 7 of 16 healthy adults taking 1,500mg a day had raised ALT (a liver enzyme), and 5 met the criteria for drug-induced liver injury. In a 2025 US FDA trial of 201 healthy adults taking about 5mg per kg of body weight a day (around 350mg for a 70kg adult), 5.6% had liver enzymes above three times the normal limit, against none on placebo.
The risk is higher alongside other medicines that affect the liver: in the Epidyolex trials, raised ALT happened mostly in people also taking valproate, and there isn’t enough data on other such medicines. If you have regular liver blood tests, talk to your doctor before using CBD. More in is CBD bad for your liver?
CBD balms and creams
Much less CBD is thought to reach the bloodstream from a balm or cream than from an oil or capsule, so interactions are less likely, though this has been studied far less. If you take a high-risk medicine such as warfarin, tacrolimus or an epilepsy medicine, check with a pharmacist before using any CBD product. See CBD balm: what it is and how to use it.
What the FSA advises, and who should avoid CBD
The Food Standards Agency (FSA) says that, as a precaution, it does not recommend CBD for people in vulnerable groups unless under medical direction. That includes:
- people taking any medication
- children (under 18)
- anyone trying to conceive, pregnant or breastfeeding
Its labelling guidance adds that anyone taking medication or who is immunosuppressed should consult a healthcare professional first. Our products are for adults (18+) only. We don’t recommend our products during pregnancy or breastfeeding (see CBD in pregnancy).
How to use CBD more safely
- Ask your pharmacist with your full medicine list, including the CBD product and how many mg a day it gives. It’s free and quick.
- Talk to your prescriber first if you take warfarin, an epilepsy or transplant medicine, or anything with regular blood level checks.
- Start low and increase slowly.
- Keep it steady. Take the same amount, the same way (with or without food), each day. Big changes are more likely to shift medicine levels.
- Don’t rely on spacing doses. After a week of regular prescription doses, CBD’s half-life was 56 to 61 hours, so taking it a few hours away from a medicine doesn’t separate them. See how long CBD stays in your system.
- Tell the team that does your blood tests, such as INR checks for warfarin, drug level checks or liver tests.
- Never stop or change a prescribed medicine to make room for CBD.
- Choose THC-free, lab-tested CBD, so you know what you’re taking.
Signs of an interaction
Stop CBD and contact your GP or pharmacist if you notice unusual drowsiness, dizziness, unexpected bruising or bleeding, stronger side effects from your usual medicine, or yellowing of the skin or eyes. Call 999 for severe symptoms such as heavy bleeding, chest pain or difficulty breathing. For CBD’s own side effects, see CBD side effects.
Guides to specific medicines
- Erection medicines: CBD with erection medicines and other sex-related questions
- Heart and blood pressure: CBD and heart palpitations and low blood pressure
- Colchicine: CBD and gout medicines
- Turmeric and black pepper: CBD and turmeric together
- Baclofen and gabapentin: CBD and MS medicines
- Azathioprine, methotrexate, steroids and biologics: CBD for Crohn’s
- Pregabalin, amitriptyline or duloxetine for nerve pain: CBD and sciatica
- Herbal supplements: CBD and ashwagandha
- Timing: CBD oil timing: morning or night
- Driving warnings: CBD, medicines and driving
If you take diabetes medicines, read CBD and diabetes: blood sugar, medicines and safety before trying CBD, and check with your GP or pharmacist.
If you take transplant medicines such as tacrolimus, read CBD, kidney disease and transplant safety and speak to your kidney team first.
If you take painkillers, see the safety section of our best CBD oil for pain UK guide.
Turmeric can also interact with blood thinners and other medicines: see who should avoid turmeric supplements.
Curious what a normal response looks like? See what does CBD feel like?
FAQs
Can CBD interact with medications?
Yes, with some. The clearest interactions are with clobazam, valproate, tacrolimus, everolimus and warfarin, mostly at prescription doses. Ask a pharmacist before combining CBD with any regular medicine.
What does the grapefruit warning mean for CBD?
It’s a prompt to ask a pharmacist, not a reliable rule. CBD didn’t affect CYP3A4, the enzyme grapefruit blocks, in a study in people, and its clearest interactions, such as with clobazam, run through other enzymes.
Which drugs should not be taken with CBD?
Take particular care with warfarin, epilepsy medicines, transplant medicines such as tacrolimus and everolimus, and sedatives. Don’t combine them with CBD unless your doctor agrees.
Can I take CBD with antidepressants?
Speak to your GP or pharmacist first. There is little direct research, but lab data suggest CBD could change levels of some, such as bupropion, and both can cause drowsiness.
Can I take CBD with blood pressure or heart medicines?
Ask your pharmacist first. A large single dose of CBD lowered blood pressure slightly in healthy men, and digoxin levels may rise. Most heart medicines haven’t been tested with CBD.
Can I take CBD with thyroid medication?
We found no studies of CBD with levothyroxine, and a 2025 trial found CBD didn’t change thyroid hormone levels in healthy adults. Check with a pharmacist and keep your CBD amount steady.
Does CBD balm interact with medication?
Much less CBD is thought to reach the bloodstream from skin products, so interactions are less likely, but check with a pharmacist if you take high-risk medicines.
How long should I leave between CBD and my medication?
Spacing doses doesn’t reliably help. With regular use CBD stays in the body for days, so a gap of a few hours doesn’t separate it from your medicine. Ask your pharmacist instead.
Sources
- emc. Epidyolex 100 mg/ml oral solution: summary of product characteristics (sections 4.4, 4.5 and 5.2). Revised June 2026.
- Patsalos PN et al. Clinical implications of trials investigating drug-drug interactions between cannabidiol and enzyme inducers or inhibitors or common antiseizure drugs. Epilepsia, 2020.
- So GC et al. A phase I trial of the pharmacokinetic interaction between cannabidiol and tacrolimus. Clin Pharmacol Ther, 2025.
- Grayson L et al. An interaction between warfarin and cannabidiol, a case report. Epilepsy Behav Case Rep, 2018.
- Cortopassi J. Warfarin dose adjustment required after cannabidiol initiation and titration. Am J Health Syst Pharm, 2020.
- Smythe MA et al. Anticoagulant drug-drug interactions with cannabinoids: a systematic review. Pharmacotherapy, 2023.
- Herdegen T, Cascorbi I. Drug interactions of tetrahydrocannabinol and cannabidiol in cannabinoid drugs. Dtsch Arztebl Int, 2023.
- Watkins PB et al. Cannabidiol and abnormal liver chemistries in healthy adults: results of a phase I clinical trial. Clin Pharmacol Ther, 2021.
- Florian J et al. Cannabidiol and liver enzyme level elevations in healthy adults: a randomized clinical trial. JAMA Intern Med, 2025.
- Jadoon KA et al. A single dose of cannabidiol reduces blood pressure in healthy volunteers in a randomized crossover study. JCI Insight, 2017.
- Brown JD, Winterstein AG. Potential adverse drug events and drug-drug interactions with medical and consumer cannabidiol (CBD) use. J Clin Med, 2019.
- US FDA. Grapefruit juice and some drugs don’t mix.
- Food Standards Agency (GOV.UK). Cannabidiol (CBD) guidance.
