CBD Side Effects, Liver Risks and Who Should Avoid CBD

What are the most common side effects of CBD?

The clearest list comes from Epidyolex, the prescription CBD medicine approved for rare seizure disorders. Its summary of product characteristics names the most common adverse reactions as somnolence, decreased appetite, diarrhoea, fever, fatigue and vomiting (opens in a new tab). Those figures come from patients taking 10 to 25 mg per kg a day, which works out at roughly 700 to 1,750 mg a day for a 70 kg adult.

A 2020 meta-analysis pooled 12 placebo-controlled trials with 803 participants. Compared with placebo, CBD was linked to more decreased appetite, diarrhoea, somnolence and sedation, as well as more withdrawals from the trials (Chesney et al., 2020 (opens in a new tab)). Most of those links came from trials in children with epilepsy, many of whom also took clobazam or valproate. Once the authors left those trials out, diarrhoea was the only side effect that stayed more frequent with CBD.

The FDA groups the effects you might notice into three kinds: changes in alertness, mostly drowsiness; stomach and gut problems, mostly diarrhoea or reduced appetite; and mood changes, mostly irritability and agitation (opens in a new tab). The FDA says these should improve when CBD is stopped or the amount is reduced.

Common and serious side effects at a glance

Does CBD affect the liver?

Raised liver enzymes are the most studied safety signal for CBD. In the Epidyolex trials, ALT rose above three times the upper limit of normal in 12 % of patients on CBD and under 1 % on placebo (opens in a new tab). The rises were dose-related, usually appeared in the first two months, and were most frequent in patients also taking valproate.

Healthy adults have shown the same signal. In a 2025 randomised, double-blind trial run by the FDA, 201 healthy adults took CBD (5 mg per kg a day) or placebo for 28 days. Liver enzymes rose above three times the normal limit in 8 people on CBD (a Kaplan-Meier estimate of 5.6 %) and in none of the 50 on placebo, and 7 people met the trial's criteria for possible drug-induced liver injury (Florian et al., 2025 (opens in a new tab)). The FDA's summary puts that dose at 250 to 550 mg a day (opens in a new tab) and reports that nobody had liver symptoms and enzyme levels returned to normal within one to two weeks of stopping.

An earlier phase I trial gave 16 healthy adults 1,500 mg a day for about three and a half weeks. Seven had ALT above the normal limit, and in five it passed five times the limit (Watkins et al., 2021 (opens in a new tab)).

An observational study looked at people taking commercial CBD at lower amounts. Of 839 US adults who had taken it for at least 30 days (average 50 mg a day), 9.1 % had raised ALT, close to the 8.9 % seen in the general US adult population (Kaufmann et al., 2021 (opens in a new tab)). That was significantly higher than the 2.5 % expected in a healthy population with no medical conditions, and three of the 839 had ALT above three times the normal limit. The study had no placebo group, was funded by and recruited through 12 CBD companies, and excluded people with liver disease or on certain medicines.

Two points matter for anyone taking CBD. Liver changes in these studies were found through blood tests, so you would not usually feel them. And EFSA lists possible effects on the liver (opens in a new tab) among the data gaps it confirmed in 2026. The UK Food Standards Agency says the more CBD you consume over your lifetime, the more likely long-term effects such as liver damage or thyroid problems become (opens in a new tab).

Do side effects depend on the dose?

The Chesney meta-analysis covered trials that used 20 to 3,000 mg a day (opens in a new tab). At the low end of that range (20 to 400 mg), 4.3 % of participants withdrew from the trials, against 3.5 % on placebo. Withdrawals rose to 8.8 % at medium doses (600 to 1,000 mg) and 12.9 % at high doses (1,400 to 3,000 mg) (opens in a new tab). The authors called for more safety studies of over-the-counter CBD products.

The observational study in the liver section looked at people taking commercial CBD at an average of about 50 mg a day (opens in a new tab), and the Epidyolex doses work out at hundreds of milligrams or more for an adult.

CBD side effects with long-term daily use

In the 2025 trial run by the FDA, 28 days of CBD did not change testosterone, inhibin B or thyroid hormones compared with placebo (Florian et al., 2025 (opens in a new tab)). Most controlled trials so far have lasted weeks rather than years, and the FDA lists what happens with daily use over long periods (opens in a new tab) among the questions it is still working on.

EFSA's 2026 statement confirmed data gaps on possible effects on the liver and on the endocrine, nervous and reproductive systems (opens in a new tab). The FDA notes that male reproductive toxicity has been reported in animal studies (opens in a new tab) and that it is not known whether this happens in humans.

Can CBD cause grogginess or headaches the next day?

Drowsiness is one of the most consistent findings. The Epidyolex SmPC says somnolence and sedation occur more often early in treatment and may lessen over time (opens in a new tab), and that alcohol and other sedating substances can add to it.

CBD also stays in the body for a while. In a 2018 trial in healthy adults taking 750 or 1,500 mg twice daily, the effective half-life, which describes how CBD builds up and clears during regular dosing, was 10 to 17 hours (opens in a new tab). The terminal half-life, which covers the slow last phase of elimination, was about 60 hours. Headache was one of the most common adverse events in that trial, along with diarrhoea, nausea and drowsiness, and it was more frequent on CBD than on placebo. All doses in that trial were 750 mg or more.

We found no trial that measured next-day grogginess directly. For headache as a side effect and what migraine studies have tested, see CBD, headaches and migraine. If you feel drowsy after taking CBD, read our guide to CBD, drowsiness and driving before you get behind the wheel.

Is CBD safe for older adults?

A 2021 meta-analysis in PLOS Medicine pooled 46 trials of cannabinoid medicines in people with an average age of 50 or more. For CBD-only products, the estimate showed no increase in all-cause adverse events compared with control (opens in a new tab), while products containing THC increased adverse events. The CBD-only estimate came from 2 small crossover trials with participants aged 53 to 59, and the authors described the CBD-only evidence in older adults as sparse. The FDA lists the effects of CBD in the elderly (opens in a new tab) among the questions it is still working on.

The 2025 trial run by the FDA enrolled healthy adults. The FDA notes that older adults who use CBD may be at higher risk than that healthy study population (opens in a new tab).

CBD can change how other drugs work, and the FDA warns that combining it with alcohol or sedating medicines raises the risk of drowsiness that can lead to injuries (opens in a new tab). Our guide to CBD drug interactions covers which medicine groups need the most care, and we have a separate page on drowsiness with muscle relaxants.

Who should avoid CBD?

EFSA concluded in February 2026 that safety cannot be established for individuals under 25 years old, pregnant and lactating women, and those on medication (opens in a new tab).

The UK FSA does not recommend CBD, unless under medical direction, for children under 18, people taking any medication, people trying to conceive, and those who are pregnant or breastfeeding (opens in a new tab).

The Epidyolex trials and the FDA add two more groups to talk to a doctor first: people whose liver enzymes are already raised, who had higher rates of enzyme rises on CBD (opens in a new tab), and people who drink alcohol or take sedating medicines.

What happens if you take too much CBD?

In a 2018 trial, healthy adults took single doses of up to 6,000 mg (opens in a new tab). The authors reported the doses as well tolerated, with mild or moderate side effects, mostly diarrhoea, nausea, headache and drowsiness. Those were single doses given under clinical supervision. The liver findings above came from repeated dosing over weeks.

Taking more than the label states, or combining several CBD products, raises the amount you take each day.

Do side effects differ between capsules, oils and gummies?

The trials above gave CBD by mouth, mostly as an oral solution, so their findings apply to oral products in general, including capsules and gummies. We found no trial that compared side effects between oral formats. For creams, vapes and other non-oral products, the FDA lists how the method of use affects intake (opens in a new tab) as an open question, so the findings above should not be read across to them. What changes between formats is how much CBD you take and how consistently. Our page on CBD capsules vs oil explains how dosing differs.

One factor that does matter is food. In the 2018 trial, a high-fat meal increased CBD levels in the blood about four- to five-fold (opens in a new tab).

What to do if you notice side effects

1. Stop taking the product. The FDA says noticeable side effects should improve when CBD is stopped or the amount is reduced (opens in a new tab).
2. Contact a doctor or pharmacist, especially if you take any medicine or have a liver condition. The FDA notes that liver injury from CBD was found through blood tests (opens in a new tab), so a clinician can check for it even when you feel well.
3. Write down the product name, batch number, CBD per serving, when you took it, what else you took (medicines, supplements, alcohol) and when the symptoms started. This helps a clinician judge whether CBD is the likely cause.
4. Report it. In the UK, the FSA takes reports of food safety problems through its report a food problem page (opens in a new tab). In EU countries, contact your national food safety authority.

The FDA also advises caution when combining CBD products with herbs or other dietary supplements (opens in a new tab), because little research exists on those interactions.

Frequently asked questions