Randomized Controlled Double Blind Trial of Short vs Long Acting Dihydrocodeine in Chronic Non-malignant Pain

"Group 1: 2\* 60 mg dihydrocodeine long acting + up to four placebo short action~Group 2: 3\* 60 mg dihydrocodeine long acting + up to six placebo short action~Group 3: 4\* 60 mg dihydrocodeine long acting + up to eight placebo short action~Group 4: 2 placebo for long acting + up to 4\*30 mg dihydrocodeine short acting~Group 5: 3 placebo for long acting + up to 6\*30 mg dihydrocodeine short acting~Group 6: 3 placebo for long acting + up to 8\*30 mg dihydrocodeine short acting"