CBD and the liver: what blood tests show, dose by dose

A liver panel measures several enzymes. The transaminases, ALT and AST, sit inside liver cells. When those cells are damaged, they release them into the blood and the measured level goes up. CBD studies use one threshold: three times the upper limit of normal. Above it, the rise is considered clinically notable. Combined with a raised bilirubin and no other explanation, it signals serious liver injury, as the Epidyolex summary of product characteristics points out.

A rise is not liver disease. But it shows the organ is reacting, and it justifies stopping the product involved or lowering the dose.

The data come from very different populations: consumers, healthy volunteers, children with epilepsy on several treatments. The chart ranks them by dose without pretending to draw a single curve.

The randomised trial run by the FDA, published in 2025 in JAMA Internal Medicine, is the most useful for a consumer. It gave purified CBD or a placebo to 201 healthy adults, at 2.5 mg/kg twice a day, or 250 to 550 mg a day, for 28 days. Eight people on CBD out of 151 went above three times normal, none on placebo. Seven reached the stopping threshold set for possible drug-induced liver injury. None had symptoms, and levels returned to normal one to two weeks after stopping.

At higher doses, the signal climbs. In a phase I trial published in 2021, 16 healthy adults received up to 1,500 mg a day. Seven saw their ALT go above normal, five beyond five times normal, and six had to leave the study. The rises appeared between the second and fourth week.

At the other end, a 2023 observational study followed 839 consumers of shop products, at 50 mg a day on average. The share with ALT above normal, 9.1%, was close to that of the general US population. Only three people went above three times normal. The study had no control group and was funded by twelve CBD companies, which calls for a cautious reading.

Epidyolex is the only authorised CBD-based medicine. Its summary of product characteristics, published by the European Medicines Agency, gives the most complete figures. In controlled trials, 12% of patients on CBD went above three times normal, against less than 1% on placebo.

The same document identifies the risk factors:

• the 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% with clobazam as well, against 3% with neither;
• an already abnormal panel: 29% had rises when ALT was above normal at the start, against 12%.

Rises usually occur in the first two months, sometimes up to 18 months in patients on valproate. The doctor orders transaminase tests before treatment, then at 1, 3 and 6 months.

The liver clears CBD through the cytochrome P450 enzymes and the UGT enzymes, the same ones that handle a large share of medicines. CBD slows several of them down. According to the Epidyolex summary of product characteristics:

Narrow-margin medicines, where the effective dose is close to the toxic dose, are the most affected. Our article on the grapefruit effect explains this mechanism. In practice, tell your doctor or pharmacist about any CBD product, as you would a food supplement.

EFSA published on 9 February 2026 a provisional safe level of 0.0275 mg of CBD per kilo per day, or about 2 mg for a 70 kg adult. The agency lists the liver among its data gaps. It considers that the safety of CBD cannot be established under 25, during pregnancy or breastfeeding, or in people on medication. Our article on the EFSA reference dose converts this benchmark into drops.

The doses linked to enzyme rises remain far above it: 250 mg a day is more than a hundred times this benchmark. Between 2 and 250 mg, human data are scarce.

Be more careful if you:

• have a known liver disease or an already abnormal liver panel;
• take a long-term treatment, especially an antiepileptic, an anticoagulant or an immunosuppressant;
• drink alcohol regularly.

Enzyme rises cause no symptoms at first. If you take CBD alongside a treatment monitored by blood tests, mention it to the prescriber. Our article on the side effects of CBD covers the other adverse effects described.