Researchers at University College London and Great Ormond Street Hospital for Children NHS Foundation Trust (GOSH) are set to begin two clinical trials in 2025 to explore the effectiveness of cannabis-based medicines in treating severe forms of epilepsy. The trials, initiated almost six years after the legalization of medical cannabis in the UK, aim to address the critical need for evidence-based treatments for epilepsy patients.
Trial Design and Objectives
The first trial will focus on both adult and pediatric patients with epilepsies that began in the first three years of life. The second trial will investigate patients with genetic generalized epilepsies (GGE) that have not responded to standard treatments. Across multiple NHS sites in the UK, 500 participants will be randomized to receive either CBD, a combination of CBD and THC, or a matched placebo. Researchers will evaluate the safety and efficacy of these medicines in reducing seizure frequency, as well as their impact on learning, sleep, behavior, quality of life, stress, and anxiety.
Professor Finbar O’Callaghan, Co-Chief Investigator at UCL Great Ormond Street Institute of Child Health and Honorary Consultant at GOSH, stated, “For patients with difficult-to-treat epilepsies, cannabis-based medicinal products are promising treatments, but it is essential that we have high-quality evidence from robust clinical trials to be sure they are effective and do not have harmful effects. Only with this evidence will we establish whether these medicines might have a place alongside existing anti-seizure medications.”
Concerns Over Trial Design
Despite the anticipation, experts and patient advocates have voiced concerns regarding the trial design. Hannah Deacon, along with Professor Mike Barnes, highlighted several issues, including the mandatory eight-week washout period during which participants must abstain from all cannabinoid medications. Deacon warned that this washout period could be dangerous and potentially life-threatening for some patients.
Another concern is the trial's exclusive use of CBD and THC isolates, rather than full-spectrum cannabis products. Professor Barnes noted that while CBD isolate is effective for epilepsy, as demonstrated by drugs like Jazz Pharmaceuticals’ Epidyolex, full-spectrum products, which include other cannabinoids and terpenes, often yield better results due to the entourage effect. He also criticized the use of terpenes as a placebo, given their inherent medicinal properties, including anticonvulsant effects.
Professor Barnes explained, "In my experience, you get a better response if you use a little bit… of THC in a full-spectrum product. In my view, comparing a CBD isolate with a CBD plus THC isolate is not likely to show any difference between the two… I think they’re likely to be the same."
The Need for Personalized Medicine
The epilepsy community is increasingly advocating for personalized medicine approaches, moving away from the traditional “one size fits all” model. Treatment-resistant epilepsy affects approximately 35,000 individuals in the UK, representing about one-third of all epilepsy cases. Matt Hughes, Co-Founder and Director of Medcan Family Foundation, emphasized the variability in how children respond to medications, including cannabinoids, due to differing metabolic processes and underlying triggers.
Hughes stated, “No two children are identical to underlying triggers and how they display seizures. Children metabolise medications differently and thus have differing responses, this is true of cannabinoids also... For 40 years the figure of 30% who live with uncontrolled seizures has never fallen. There is now a call from across the epilepsy community for change, to look towards innovation, to fast-track medicines to those with an urgent unmet need. The reliance on the RCT and a trial and error approach has failed so many diagnosed with uncontrolled epilepsy.”
Families' Perspectives
Families from the campaign group End Our Pain have also expressed reservations about the trials, particularly the focus on randomized controlled trials that may not accommodate individualized dosing or whole plant preparations. They worry that the controlled dosing and potential washout periods could jeopardize the progress achieved with existing whole-plant treatments.
Despite government promises to prioritize children with severe drug-resistant epilepsy, families report facing significant barriers to accessing the medications that have proven effective for their children. With fewer than five NHS prescriptions issued for unlicensed cannabis-based medicinal products (CBPMs), many families are forced to pay up to £2,000 per month to access these treatments privately.
The group continues to advocate for NHS access to unlicensed cannabis-based medicines, highlighting the financial strain on families and the need for observational trials using full-extract cannabis preparations to demonstrate their safety and efficacy.
