Cannabidiol (CBD) to 27 Patients (Aged 2 Years - 19 Years) With Drug Resistant Epilepsy

Part A: To evaluate the safety and tolerability of multiple ascending doses of GWP42003-P compared with placebo with respect to: * Incidence, type and severity of adverse events (AEs) * Effect on vital signs, including weight * Effect on 12-lead electrocardiogram (ECG) findings * Effect on laboratory parameters Part B: To make an assessment of the anti-epileptic efficacy of GWP42003-P compared with placebo with respect to the incidence in convulsive seizures * To determine the plasma concentration time curves for GWP42003-P and its major human metabolite, following escalating multiple doses of GWP42003-P. * To investigate the effect of GWP42003-P on the pharmacokinetics of concomitant anti-epileptic drugs (AEDs). * To evaluate cognitive function, sleep quality and daytime sleepiness, in patients taking GWP42003-P in combination with AEDs.