Short answer
Yes. Cannabis oil can affect the liver. The clearest evidence comes from high-dose cannabidiol (CBD). In trials of the prescription CBD drug Epidiolex, liver enzymes rose above 3 times the upper limit of normal in a share of patients. The FDA label lists hepatotoxicity as a warning and tells doctors to run liver blood tests before treatment and during it.
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Low-dose CBD and THC oils sold outside pharmacies are studied less. Harm is possible. Harm at low doses is not measured well.
What the trials found
- Patients took 10 mg/kg or 20 mg/kg of CBD per day. That is 700 mg to 1,400 mg for a 70 kg adult. Common retail doses are 10 mg to 50 mg.
- ALT rises above 3 times the upper limit occurred in a minority of patients. Rates were higher at 20 mg/kg than at 10 mg/kg, and higher than placebo.
- Most enzyme rises fell back after a dose drop or stop. Some patients had to stop the drug.
- Liver injury was more frequent in patients who also took valproate.
Who carries more risk
- People taking valproate or other anti-seizure drugs.
- People with existing liver disease or hepatitis.
- People taking high daily CBD doses, above 300 mg.
- Children in epilepsy trials, the group studied most.
- People who drink alcohol or take acetaminophen at high doses.
Interactions
CBD blocks the CYP2C19, CYP2C9, and CYP3A4 enzymes. These enzymes clear many drugs. CBD can raise blood levels of clobazam, topiramate, and other drugs. It also changes how the body handles valproate. Drug interactions raise liver risk.
Symptoms to watch
Fatigue, nausea, vomiting, stomach pain, dark urine, pale stool, yellow eyes or skin, and pain in the upper right abdomen. Symptoms can appear with no warning. Blood tests find damage before symptoms start.
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Monitoring
The Epidiolex label calls for ALT, AST, and bilirubin tests at baseline and at 1, 3, 6, and 12 months, and after dose increases. For CBD bought outside a pharmacy, no monitoring standard exists. A doctor can order the same panel.
What is not known
Data on long-term low-dose CBD is thin. Data on THC-dominant oils and on full-spectrum products is thinner. Labels on retail products do not always match the contents. Study groups mix alcohol use, body weight, and metabolic disease with cannabis use, which makes cause and effect hard to separate.