Study identification

We searched MEDLINE and EMBASE online databases using a combination of keywords, MeSH headings, and words commonly used to describe LTOT, such as persistent or chronic use of opioids. The search strategy was undertaken after consultation with the information specialist of UNSW Sydney library in July 2018 and updated in August 2019 (see Supplementary Appendix A). We also conducted a manual search of the references of included studies and published systematic reviews for any additional articles not captured by our search strategy.