Spasticity is a major determinant of disability and decline in quality of life in patients with motor neuron disease. Cannabinoids have been approved for symptomatic treatment of spasticity in multiple sclerosis. We investigated whether cannabinoids might also reduce spasticity in patients with motor neuron disease.

We did an investigator-initiated, randomised, double-blind, placebo-controlled, phase 2 clinical trial at four tertiary motor neuron disease centres in Italy. Eligible patients were aged 18–80 years; had possible, laboratory-supported probable, probable, or definite amyotrophic lateral sclerosis as defined by revised El Escorial criteria, or primary lateral sclerosis according to Pringle’s criteria; had spasticity symptoms due to motor neuron disease for at least 3 months; had spasticity scores of 1 or greater in at least two muscle groups on the Modified Ashworth Scale; and were taking an antispasticity regimen that was maintained at a stable dose for 30 days before enrolment. Participants were assigned (1:1) by an independent statistician via a computer-generated randomisation sequence to a standardised oromucosal spray (nabiximols) containing a defined combination of delta-9-tetrahydrocannabinol and cannabidiol (each 100 μL actuation contained 2·7 mg delta-9-tetrahydrocannabinol and 2·5 mg cannabidiol) or to placebo for 6 weeks. Participants self-titrated during the first 14 treatment days according to a predefined escalation scheme (maximum 12 actuations per 24 h), then maintained that dose for 4 weeks. The primary endpoint was the change in the score on the Modified Ashworth Scale, which was assessed at baseline and after 6 weeks. Safety and tolerability were also monitored. Participants, investigators, site personnel, and the study statistician were masked to treatment allocation. All randomised participants who received at least one dose of study drug were included in the analysis. This trial is registered with ClinicalTrials.gov, number NCT01776970. The trial is closed to new participants with follow-up completed.

Between Jan 19, 2013, and Dec 15, 2014, 60 participants were randomly assigned, and 59 participants were included in the final analysis (29 in the nabiximols group and 30 in the placebo group). Modified Ashworth Scale scores improved by a mean of 0·11 (SD 0·48) in the nabiximols group and deteriorated by a mean of 0·16 (0·47) in the placebo group (adjusted effect estimate −0·32 [95% CI −0·57 to −0·069]; p=0·013). Nabiximols was well tolerated, and no participants withdrew from the double-blind phase of the study. No serious adverse effects occurred.

In this proof-of-concept trial, nabiximols had a positive effect on spasticity symptoms in patients with motor neuron disease and had an acceptable safety and tolerability profile. These findings should be investigated further in larger clinical trials.

Italian Research Foundation for Amyotrophic Lateral Sclerosis.