 3. Double Blind Treatment Phase This is a 5 week 35 day treatment period where subjects deemed to be a responder during the single blind phase will be randomized to double blind treatment with the dose of nabilone achieved at the last week Visit 5 of the single-blind phase the dose which optimized NeP relief with side effect tolerability or placebo. Subjects will be randomized to 1 of 2 treatment groups in a 1:1 ratio, nabilone or placebo respectively. Those subjects randomized to placebo will be directly switched from active drug to placebo for the duration of the study. All subjects will maintain their pre-study doses of analgesic medication for pain control throughout the study. No further dose adjustments will be allowed during Week 4 onward. 