GW Pharmaceuticals plc's add-on therapy for focal seizures failed to meet the main goal in a phase 2a trial.

The placebo-controlled study evaluated the efficacy and safety of the cannabinoid drug GWP42006 in 162 adult patients with inadequately controlled focal seizures.

GWP42006, which features cannabidivarin as the primary cannabinoid molecule, did no better than placebo in reducing focal seizures, with comparable reductions of about 40% in both the placebo and drug arms.

Cannabidivarin is a nonpsychoactive cannabinoid found in cannabis that reportedly has therapeutic efficacy in the treatment of pain, mood disorders and inflammatory diseases.

The company said the extent of the placebo response is substantially greater than that seen in studies of other treatments in similar patient populations, and it is now working to understand the potential reasons for this result.

Among patients receiving the drug, 73% experienced treatment-emergent adverse events compared to 48% of patients in the placebo group. A majority of the GWP42006 patients experienced adverse events of mild or moderate severity. The incidence of serious adverse events was low — 3.7% on the drug compared to 1.2% on placebo.

The biopharmaceutical company plans to continue to study the drug in other areas, including autism spectrum disorders and epilepsy.