Subjects who have previously participated in GWCA0101, a two week (two days baseline and two weeks treatment period), multicentre, double blind, randomised, placebo controlled, parallel group study to evaluate the efficacy of Sativex® (containing delta-9-tetrahydrocannabinol [THC] and cannabidiol [CBD]) and GW-2000-02 (containing THC alone) in subjects with cancer-related pain are screened, and if eligible begin dosing with open-label Sativex®. They are allowed to self-titrate their study medication to symptom resolution or maximum tolerated/allowable dose of 130 mg THC and 120 mg CBD and have the opportunity to request a change from Sativex® to GW-2000-02 if they or the investigator consider their response less than optimal. Subjects are reviewed for tolerability and evidence of clinical benefit at 7-10 days after Visit 1 and then every four weeks. Continuation within the study is conditional on satisfactory reports of tolerability, efficacy and dosing regime.