Researchers sought to determine if Skeletal muscle relaxants (SMR) efficacy was related to age, gender, or baseline Low back pain (LBP) severity for a study. Planned data analysis from 4 randomized studies of patients with acute nonradicular LBP was conducted. Patients were enrolled in the study during an emergency room visit and followed up a week later. The Roland-Morris Disability Questionnaire (RMDQ) scores improved between the emergency rooms (ED) discharge and the 1-week follow-up. The effects of placebo, baclofen, metaxalone, tizanidine, diazepam, orphenadrine, methocarbamol, and cyclobenzaprine on RMDQ were compared. A nonsteroidal anti-inflammatory medicine was also given to all of the patients. Investigators used analysis of variance to determine whether there were any statistically significant differences across medications and linear regression to see if age, sex, and baseline severity affected the immediate result. The mean improvement in RMDQ was 10.5 (95% CI 9.5–11.5) for placebo, 10.6 (95% CI 8.6–12.7) for baclofen, 10.3 (95% CI 8.1–12.4) for metaxalone, 11.5 (95% CI 9.5–13.4) for tizanidine, 11.1 (95% CI 9–13.2) for diazepam, orphenadrine 9.5 (95% CI The differences between groups were not statistically significant. Regardless of age, gender, or baseline severity, the results were similar. Greater clinical improvement was associated with a higher baseline RMDQ (B coefficient 5.7, p<0.01). Cyclobenzaprine was associated with greater adverse drug effects than placebo (p<0.01). SMRs did not enhance outcomes more than placebo in patients in the ED with acute LBP treated with a nonsteroidal anti-inflammatory medication. The outcomes were unaffected by age, gender, or baseline disability.