CBD and the liver: what blood tests show, dose by dose
CBD can raise liver enzymes, and the risk climbs with the dose. In an FDA trial, 5.6% of healthy adults had levels above three times the upper limit of normal after four weeks at 5 mg/kg a day, all without symptoms. An observational study of consumers taking about 50 mg a day found just 0.36%. For most people, the more practical concern is different: CBD slows the clearance of several medicines.
Key takeaways
- ALT (alanine aminotransferase) is the marker to follow: this enzyme leaks into the blood when liver cells are strained.
- With Epidyolex, levels above three times normal occurred in 3% of patients at 10 mg/kg a day and in 15% at 20-25 mg/kg.
- Among healthy adults taking 250 to 550 mg a day for 28 days, 8 out of 151 had such rises.
- Nothing is felt, so only a blood test detects these rises; levels normalised one to two weeks after stopping.
- EFSA's provisional reference is about 2 mg a day for 70 kg, and it leaves out people on medication.
What a blood test measures
Several enzymes are measured in a liver panel. Two of them, the transaminases ALT and AST, are found inside liver cells. Damaged cells release them into the blood, and the measured level rises. CBD studies all use the same threshold, three times the upper limit of normal, beyond which a rise counts as clinically notable. The Epidyolex summary of product characteristics notes that such a rise, with raised bilirubin and no other explanation, signals serious liver injury.
A raised level does not mean liver disease. It does show that the organ is reacting, which is reason enough to stop the product involved or lower the dose.
From the bottle to the medicine: five studies, five dose levels
The populations behind these data differ widely: consumers, healthy volunteers, and children with epilepsy on several treatments. The chart orders them by dose and makes no attempt to draw a single curve.
| Study | Population | CBD dose | Above 3 times normal |
|---|---|---|---|
| Kaufmann, 2023, observational | 839 consumers | 50 mg a day on average | 0.36% |
| FDA, 2025, randomised, placebo-controlled | 151 healthy adults on CBD | 250 to 550 mg a day, 28 days | 5.6% (placebo: 0%) |
| Epidyolex, controlled trials | Patients with epilepsy | 10 mg/kg a day | 3% |
| Epidyolex, controlled trials | Patients with epilepsy | 20 to 25 mg/kg a day | 15% |
| Watkins, 2021, phase I | 16 healthy adults | 1,500 mg a day | 38% |
For a consumer, the most relevant study is the randomised trial run by the FDA, published in 2025 in JAMA Internal Medicine. For 28 days, 201 healthy adults took purified CBD or a placebo, at 2.5 mg/kg twice a day, which is 250 to 550 mg a day. Eight of the 151 people on CBD went above three times normal, against none on placebo. Seven reached the stopping threshold for possible drug-induced liver injury. Nobody had symptoms, and levels were back to normal one to two weeks after stopping.
The signal grows stronger at higher doses. In a phase I trial published in 2021, 16 healthy adults took up to 1,500 mg a day. ALT went above normal in seven of them and beyond five times normal in five, and six had to leave the study. The rises showed up between the second and the fourth week.
At the low end, a 2023 observational study followed 839 people using shop products, on average 50 mg a day. ALT was above normal in 9.1% of them, near the rate in the general US population, and three people exceeded three times normal. Twelve CBD companies funded the study, which had no control group, so read it with caution.
What the Epidyolex leaflet says
Epidyolex, the only authorised CBD-based medicine, comes with the fullest figures in its summary of product characteristics, published by the European Medicines Agency. In controlled trials, levels above three times normal occurred in 12% of patients on CBD and in less than 1% on placebo.
The document names three risk factors:
- dose: 3% of patients at 10 mg/kg a day, 15% at 20 or 25 mg/kg;
- valproate, an antiepileptic: 19% of patients taking it, 23% when clobazam was added too, against 3% with neither;
- a liver panel already abnormal: 29% had rises when ALT was above normal at baseline, against 12%.
Most rises appear within the first two months, and in patients on valproate sometimes as late as 18 months. The doctor checks transaminases before treatment starts, then at 1, 3 and 6 months.
The most common risk: drug interactions
CBD is cleared by the liver's cytochrome P450 and UGT enzymes, which also process a large share of medicines, and it slows several of them. The Epidyolex summary of product characteristics reports the following:
| Situation | Measured effect |
|---|---|
| CBD and clobazam | Active metabolite of clobazam multiplied by 3 to 4, via the CYP2C19 enzyme |
| CBD at 1,500 mg a day and caffeine | Caffeine exposure increased by 95% |
| CBD and everolimus, an immunosuppressant | Everolimus exposure multiplied by about 2.5, blood level monitoring recommended |
| CBD and St John's wort, rifampicin or carbamazepine | CBD level lowered by these enzyme inducers |
| CBD and alcohol | CBD exposure increased by 63%, stronger drowsiness |
Medicines with a narrow margin, where the effective dose sits close to the toxic one, are the most affected. The mechanism is explained in our article on the grapefruit effect. In practice, mention any CBD product to your doctor or pharmacist, just as you would a food supplement.
What dose, and who should abstain
EFSA published on 9 February 2026 a provisional safe level of 0.0275 mg of CBD per kilo per day, about 2 mg for an adult of 70 kg. The liver is one of the data gaps it lists. In the agency's view, the safety of CBD cannot be established under 25, during pregnancy or breastfeeding, or for people on medication. Our article on the EFSA reference dose turns this benchmark into drops.
Enzyme rises have been tied to doses far above that level: 250 mg a day is over a hundred times the benchmark. Human data between 2 and 250 mg are scarce.
Take extra care if you:
- already have a liver disease or an abnormal liver panel;
- are on long-term treatment, an antiepileptic, an anticoagulant or an immunosuppressant in particular;
- drink alcohol on a regular basis.
At first, raised enzymes produce no symptoms. If your treatment is monitored by blood tests and you also take CBD, tell the prescriber. The other reported adverse effects are covered in our article on the side effects of CBD.
Frequently asked questions
It can raise liver enzymes, mainly at high doses: in the FDA trial, 5.6% of healthy adults taking 250-550 mg a day. At around 50 mg a day, a study with no control group found a rate near that of the general population.
Documented rises begin at about 5 mg/kg a day, roughly 350 mg for 70 kg. Below that, the data are too thin to set a threshold. EFSA's provisional benchmark is 2 mg a day.
It can. CBD inhibits the CYP2C19 enzyme in particular, and CYP1A2 more weakly, so the blood level of other drugs can go up. Ask your pharmacist before combining them.
No guideline requires one at shop doses. Monitoring is mandatory on Epidyolex. If your liver panel is already followed for another reason, tell the doctor who orders it that you take CBD.
Written by the Phytogrammes team
Each journal article draws on cited primary sources: ANSM, EFSA, EUR-Lex and peer-reviewed publications. Product profiles are distinguished from documented laboratory results. Our approach.
Article published on . CBD is not a medicine.