A Cochrane review «Opioids compared to placebo or other treatments for chronic low‐back pain»1 «Chaparro LE, Furlan AD, Deshpande A et al. Opioids...»1 included 15 studies with a total of 5540 subjects. Tramadol was examined in five trials with 1378 participants, transdermal buprenorphine in two trials with 653 participants and strong opioids (morphine, hydromorphone, oxycodone, oxymorphone, and tapentadol) in six trials with 1887 participants.
Tramadol was found to be better than placebo for pain (SMD -0.55, 95% CI -0.66 to -0.44) and function (SMD -0.18, 95% CI -0.29 to -0.07). Transdermal buprenorphine may make little difference for pain (SMD -2.47, 95%CI -2.69 to -2.25), but no difference compared to placebo for function (SMD -0.14, 95%CI -0.53 to 0.25). Strong opioids (morphine, hydromorphone, oxycodone, oxymorphone, and tapentadol), were better than placebo for pain (SMD -0.43, 95%CI -0.52 to -0.33) and function (SMD -0.26, 95% CI -0.37 to -0.15).
Comment: The level of evidence is downgraded by study quality (inadequate intention-to-treat adherence and study duration) and limited interpretation of functional improvement.