A new review undertaken by academics fromThe University of New South Wales, published in the Journal of Neurology Neurosurgery & Psychiatry, assessed six clinical trials (555 patients) and 30 observational studies (2,865 patients).
All the participants, whose average age was 16, had rare forms of epilepsy that had not responded to usual treatment.
Pooled analysis of the clinical trial data showed that CBD was more effective than a placebo at cutting seizure frequency by 50% or more, and at improving quality of life.
CBD was also more effective than placebo at eradicating seizures altogether, although this was still rare.
But the risk of side effects (dizziness and drowsiness), although small, was significant — 24% higher — while that of serious side effects was twice as high among those taking cannabidiol.
Data from 17 of the observational studies, meanwhile, showed that seizure frequency dropped by at least 50% in just under half of the patients and disappeared completely in nearly one in 8.5% of subjects. Quality of life improved in half of the patients in 12 of the studies.
New findings imminent
"Pharmaceutical-grade CBD as adjuvant treatment in paediatric onset drug resistant epilepsy may reduce seizure frequency," concluded the researchers.
"Existing (randomised controlled trial) evidence is mostly in paediatric samples with rare and severe epilepsy syndromes; (randomised controlled trials) examining other syndromes and cannabinoids are needed."
The evidence to date is confined to the treatment of children and teens whose epilepsy does not respond to conventional drugs, and rare and serious forms of the condition, cautioned the researchers.
Between 70% and 80% of people newly diagnosed with epilepsy manage to control their seizures completely using conventional drugs such as valproate and carbamazepine, but that still leaves up to a third whose condition is unresponsive to these treatments.
The researchers added: "Well-controlled and well-regulated therapeutic trials are essential to specify the doses required to produce therapeutic effects with a minimum of adverse effects.
"We identified an additional 10 studies that met inclusion criteria but for which results were not yet posted. As these results become available, we hope to see these included in updated reviews in order to improve recommendations on the use of cannabinoids for treatment-resistant epilepsy."