CBD and your liver in the UK: the blood test to do first

1. What did the CBD liver trial actually find?

Raised liver enzymes in about one person in eighteen. None of them felt it.

The trial was published in JAMA Internal Medicine on 7 July 2025. It was randomised, placebo-controlled and double-blinded, which is the strongest design medicine has. 201 healthy adults took part. 151 took CBD, 50 took a placebo, for 28 days.

• Eight people, 5.6%, went past three times the limit. That is the trial's main finding. On placebo, nobody did.
• Seven had to come off the trial. They met the study's own stopping rules for possible drug-induced liver injury. Two stopped on day 21, five on day 28.
• Two went past ten times the limit. The highest reading was more than eighteen times. Those are not small numbers.
• It reversed. Everyone started healthy and enzymes settled after stopping. This was a signal, not a wave of liver failure.

The FDA's own write-up makes the practical point. People do not feel a rising ALT, so the agency says the findings highlight “the need for caution and potentially routine monitoring in CBD users”. That is the argument for a blood test rather than wait-and-see.

2. Is that the dose in your gummies?

Almost certainly not. The gap is the useful part.

The trial used 5mg of CBD per kilogram of body weight per day. For a 70kg adult, that works out at roughly 350mg a day. The FSA advises healthy adults to keep CBD from food to 10mg a day. The trial dose was about thirty-five times that.

So a 10mg gummy is not the trial. A high-strength oil taken daily sits closer than most people realise. The FSA figure is advice rather than law, and the trial team noted their dose falls inside the range some people reach with unregulated products.

“The more CBD you consume over your lifetime, the more likely you are to develop long-term adverse effects, like liver damage or thyroid issues.”

Food Standards Agency, consumer advice on cannabidiol

The FSA also advises against CBD for children, anyone taking medication, and anyone pregnant, breastfeeding or trying to conceive. The thyroid mention is not a throwaway. Our thyroid hub covers which markers read it.

3. Which blood markers show liver strain?

ALT first. Read it with the rest of the liver set, never on its own.

• ALT, the early one. ALT is an enzyme held inside liver cells. It leaks into the blood when those cells are under strain, so it rises before you feel anything. It is the marker the trial tracked. Our ALT blood test guide covers the range, and high ALT levels explains why one raised reading is usually not alarming.
• ALP, read alongside. Alkaline phosphatase is a second liver enzyme, tied to the bile ducts. The pattern between the two tells a clinician which part of the liver is complaining. See the ALP guide.
• Albumin and total protein. Your liver makes both. They say less about damage and more about how well the organ is doing its day job.

Helvy's Thyroid & Vital Organs panel (£159) carries ALT, ALP, albumin and total protein from a home finger-prick sample. Our liver function test guide walks through what each one reads, and liver enzyme levels by age shows what normal tends to look like at yours.

AST and GGT are the other liver enzymes a GP often orders. Neither sits on a Helvy panel. If you want those, ask your GP or start from build my test. For a broader baseline, our full blood count guide explains what that adds.

None of this diagnoses anything. A blood test measures biomarkers and offers wellness insight. A mildly raised ALT is common, often means nothing on its own, and needs a qualified clinician to read it in context. Helvy does not sell CBD.

4. When should you test, and when should you stop?

Baseline before the first dose. Repeat at about four weeks. That is the trial's window.

• Before you start. A reading taken now is the only number a later result can be compared with. Without it, a raised ALT has no history.
• Around four weeks in. The trial withdrawals happened on day 21 and day 28. That is when the signal appeared.
• One change at a time. Start CBD alongside a new liver detox blend or a turmeric course and a shifted ALT has no clear owner.
• Read the label, not the brand. Work out the milligrams per serving and the milligrams per day. Many people never do that sum.

Stop and speak to a doctor promptly if you notice yellowing of the skin or eyes, dark urine, pale stools, itching, or pain under the right ribs. The NHS puts it plainly: “Most types of liver disease do not cause any symptoms in the early stages.” Suspected reactions can be reported through the MHRA Yellow Card scheme.

One limit worth knowing. The trial enrolled healthy adults only. It says nothing about people on medicines that load the liver, heavy drinkers, or anyone with a known liver condition. Those are the groups a clinician watches most closely. Our guide to herbal supplements and liver damage covers the same question for green tea extract and ashwagandha.

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