> For a number of Key Questions, we identified no studies meeting inclusion criteria. Where studies were available, the strength of evidence was rated no higher

> For a number of Key Questions, we identified no studies meeting inclusion criteria. Where studies were available, the strength of evidence was rated no higher than low, due to imprecision and methodological shortcomings, with the exception of buccal or intranasal fentanyl[...]. No study evaluated effects of long-term opioid therapy versus no opioid therapy. > No study evaluated the effectiveness of risk mitigation strategies on outcomes related to overdose, addiction, abuse, or misuse. Evidence was insufficient to evaluate benefits and harms of long-term opioid therapy in high-risk patients or in other subgroups. > CONCLUSIONS: Evidence on long-term opioid therapy for chronic pain is very limited but suggests an increased risk of serious harms that appears to be dose-dependent. More research is needed to understand long-term benefits, risk of abuse and related outcomes, and effectiveness of different opioid prescribing methods and risk mitigation strategies. This doesn't show they aren't effective.