Cannabidiol

How it works

Its precise anticonvulsant mechanism is not fully defined but is independent of cannabinoid CB1 receptors and is thought to involve modulation of intracellular calcium and adenosine signalling.

Prescribing in practice

• It can cause dose-related transaminase elevations and hepatocellular injury, so liver function must be checked before and during treatment, especially when co-administered with valproate.
• A clinically important interaction with clobazam raises levels of its active metabolite, increasing sedation and often warranting dose review.
• Somnolence and reduced appetite are common, and abrupt withdrawal should be avoided to reduce the risk of increased seizure frequency.

Monitoring

Check liver transaminases and bilirubin before starting, periodically during treatment and after dose increases, with closer monitoring in those on valproate.

Counselling the patient

• Report yellowing of the skin or eyes, dark urine, persistent nausea or abdominal pain.
• Drowsiness is common and may be increased by other sedating medicines.
• Do not stop the medicine suddenly without medical advice.

Evidence & guidelines

Randomised controlled trials demonstrated that adjunctive cannabidiol reduces seizure frequency in Dravet and Lennox-Gastaut syndromes, supporting its NICE-appraised use.