Abstract

With the licensing of cannabidiol for drug resistant seizures in Dravet and Lennox Gastaut syndromes in the United states in 2018, interest in the potential for cannabis-based-medicinal products to meet currently unmet needs for people with epilepsy continues to grow. This review summarizes current knowledge and discusses the implications for future research and practice. Both cannabidiol and tetrahydrocannabinol, the main components, have been extensively studied in animal models, with multimodal mechanisms of action proposed. Only pure cannabidiol formulations have been rigorously evaluated in controlled trials thus far, with modest but significant improvements in motor seizures. Adverse effects include diarrhoea, somnolence and reduced appetite, with mostly acceptable tolerability, but a not insignificant (up to 1 in 23) risk of serious adverse events. Recognized drug interactions include with valproate (increased risk of hepatotoxicity) and clobazam (contributing to somnolence, increased secretions, probably chest infections, and potentially efficacy). Whilst there is public (and producer) interest in products also containing tetrahydrocannabinol, clinicians have justifiable concerns about exposing a group already vulnerable to mental health and neurobehavioural comorbidities to the associated additional risks in these domains. Artisanal preparations, with often inconsistent/unknown constituents are frequently used but not recommended. A gulf exists between the actual evidence, including a lack of comparative studies and public beliefs, fuelled by media and anecdote. Continued education of the public, policymakers, researchers and healthcare providers about what is and isn't yet known, together with on-going good quality research is essential to mitigate against future potential risks, particularly in relation to vulnerable populations.