@article{PetzkeKloseWelschetal.2020,
  author    = {Frank Petzke and Petra Klose and Patrick Welsch and Claudia Sommer and Winfried H{\"a}user},
  title     = {Opioids for chronic low back pain: An updated systematic review and meta-analysis of efficacy, tolerability and safety in randomized placebo-controlled studies of at least 4 weeks of double-blind duration},
  journal   = {European Journal of Pain},
  volume    = {24},
  number    = {3},
  pages     = {497 -- 517},
  doi       = {10.1002/ejp.1519},
  year      = {2020},
}