Sativex is an endocannabinoid system modulator principally containing Δ(9)-tetrahydrocannabinol (THC) and cannabidiol (CBD). During a 6-week randomised controlled trial, Sativex had a clinically relevant effect on spasticity associated with multiple sclerosis (MS). Patients self-titrated oromucosal Sativex to symptom relief or maximum tolerated dose (maximum of 130 mg THC and 120 mg CBD daily). The primary objective was to evaluate the safety and tolerability of long-term treatment by recording the incidence and severity of adverse events (AEs). Secondary outcomes were to determine evidence of developing tolerance and to assess the long-term dosing profile of Sativex. A validated 11-point Numerical Rating Scale of spasticity severity was used to assess efficacy. A total of 146 patients elected to enter this open-label follow-up safety trial. Mean treatment exposure was 334 days (standard deviation, SD = 209 days), and patients administered on average 7.3 (SD = 4.42) actuations per day. Fifty-two (36 %) patients withdrew from the study in the first year, 14 % due to AEs and 9 % due to lack of efficacy. Most AEs were mild/moderate in severity. Common (>10 %) treatment-related AEs were dizziness (24.7 %) and fatigue (12.3 %). Serious AEs occurred in five patients (3.4 %), with two psychiatric events reported by one patient. No psychoses, psychiatric AE trends, or withdrawal symptoms occurred following abrupt cessation of treatment. Baseline symptoms including spasticity did not deteriorate but were maintained to study completion in those patients who did not withdraw. No new safety concerns were identified with chronic Sativex treatment, and serious AEs were uncommon. There was no evidence of tolerance developing, and patients who remained in the study reported continued benefit.