There is no doubt that narcotics are effective in patients with acute pain or cancer related pain. The same does not, however, apply to chronic pain not associated with a malignancy.
There are no good quality studies in the world literature to show that narcotic pain medications work in the long term for musculoskeletal pain. (I define long term here as over nine months.)
There are studies to indicate that narcotic pain medications can be effective in the short to mid term for bone and joint pain. Such an indication might be for three months of pain control while awaiting a knee replacement.
Research studies show that patients on chronic opiate therapy have increased depression, reduced function and decreased activity.