A Cochrane review included 30 studies with a total of 2 849 subjects. Twenty-three trials were of high quality, 24 trials were on acute low back pain. Four trials studied benzodiazepines, 11 non-benzodiazepines and two antispasticity muscle relaxants in comparison with placebo. Results showed that there is strong evidence that any of these muscle relaxants are more effective than placebo for patients with acute LBP on short-term pain relief. The pooled RR for non-benzodiazepines versus placebo after two to four days was 0.80 (95% CI 0.71 to 0.89) for pain relief and 0.49 (95% CI 0.25 to 0.95) for global efficacy. Adverse events, however, with a relative risk of 1.50 (95% CI 1.14 to 1.98) were significantly more prevalent in patients receiving muscle relaxants and especially the central nervous system adverse effects (RR 2.04; 95% CI 1.23 to 3.37). The various muscle relaxants were found to be similar in performance.