CBD for drug-resistant epilepsy: trial review

When seizures continue despite treatment, an additional medicine can become part of the discussion with an epilepsy specialist. A 2026 review of seven randomised trials reports that adding CBD reduced seizure frequency compared with placebo. Its clearest findings concerned highly purified oral CBD, with different results for other formulations.

The review by Pratama and colleagues, published in Therapeutics and Clinical Risk Management, brought together trials involving 1,154 participants. It examined CBD as an add-on treatment for drug-resistant epilepsy, rather than as a replacement for existing medicines. This summary is based on the published abstract.

Why an add-on treatment matters

Epilepsy is a brain condition that causes seizures. The NHS explains that seizures affect people differently and that some remain difficult to control with medicine. For these patients and their families, the relevant question is whether another treatment can reduce seizures while fitting safely into an existing care plan.

“Adjunctive” is the term used in the paper for this add-on role. Participants received CBD alongside treatment, and the comparison groups received placebo. The study question therefore concerns an extra treatment, not what would happen if antiseizure medicines were stopped.

What the researchers brought together

The authors searched PubMed/MEDLINE, Scopus and the Cochrane trial database for randomised, double-blind, placebo-controlled trials. Random assignment determines who receives a treatment; double-blinding means participants and researchers are meant not to know the assignment.

Seven trials met the review's criteria. The authors used a meta-analysis, a method of combining study results, to examine seizure outcomes and adverse events. They also separated results by epilepsy syndrome, CBD dose and formulation.

The review covered Dravet syndrome, Lennox-Gastaut syndrome and tuberous sclerosis complex, among its reported comparisons. These are distinct diagnoses. Grouping the results does not mean that every type of epilepsy responds in the same way.

Oral CBD and other formulations had different results

The authors reported a statistically significant reduction in seizure frequency with adjunctive CBD compared with placebo. They described the effect as consistent across Dravet syndrome, Lennox-Gastaut syndrome and tuberous sclerosis complex.

In their formulation and dose analyses, they reported the strongest efficacy at 20 mg per kilogram of body weight per day of highly purified oral CBD. This is a finding about the trial treatments reviewed. It is not a dose recommendation, and it should not be used to calculate an amount of a retail CBD product.

Liposomal CBD, a formulation using small lipid-based carriers, was reported to have a more modest benefit. Transdermal formulations, designed to deliver CBD through the skin, showed no short-term efficacy in the review. The delivery method was therefore part of the result, rather than an interchangeable detail.

A reduction in seizure frequency means fewer seizures, rather than necessarily becoming seizure-free. The abstract reports the combined finding but does not give a single number of seizures avoided per participant. The result describes the groups studied, rather than predicting how much an individual person's seizures will change.

Side effects alongside existing medicines

The authors described most adverse events as mild and broadly comparable with placebo. They also reported that raised liver enzymes and somnolence, meaning unusual sleepiness, occurred more often in participants also receiving valproate or clobazam. These findings matter because the treatment was added to existing medication.

For independent context, the European Medicines Agency's information on Epidyolex describes a prescription medicine containing cannabidiol, authorised for specified epilepsy conditions. Its use and monitoring are governed by medical prescribing. That context helps explain why evidence for highly purified medicinal CBD cannot be transferred to an ordinary CBD oil.

A clearer answer about formulation

The review supports the authors' conclusion that oral CBD can have a useful add-on role in the drug-resistant epilepsies studied. It also shows why “CBD for epilepsy” is an incomplete description: the formulation, the diagnosis and the other medicines are central to understanding the result.

The authors call for further research on long-term outcomes, dosing and formulations. For a person with ongoing seizures, the finding is relevant to a specialist-led conversation about treatment options. It does not establish that a non-prescription CBD product offers the same seizure reduction or monitoring as the medicines studied.