Clinical Question

Do muscle relaxants provide relief for nonspecific lower back pain?

Bottom Line

Nonsteroidal anti-inflammatory drugs are a better choice for the treatment of low back pain. Despite benzodiazepine and nonbenzodiazepine muscle relaxants being used for almost 50 years to treat low back pain, the supporting evidence is of low certainty. None of the treatments will produce a clinically important difference over placebo. (Level of Evidence = 1a-)

Synopsis

The researchers searched eight databases, including the Cochrane Library, as well as conference abstracts and trial registries, identifying 49 trials (N = 6,505) that evaluated efficacy and acceptability. The authors included randomized clinical trials published in English, Italian, Portuguese, Spanish, German, and Dutch that compared a benzodiazepine or nonbenzodiazepine muscle relaxant with placebo, usual care, waiting list, or no treatment. In 16 trials, participants taking a nonbenzodiazepine muscle relaxant (n = 4,546) reported a pain intensity that was an average of 7.7 points lower (on a 100-point scale; 95% CI, 3.3 to 12.1) at two weeks than the average pain intensity reported by participants in a control group (a difference of less than 10 points is not clinically important). When examining only published studies, the difference in pain relief increased to an average of 10.2 points (95% CI, 4.7 to 15.6).

Analyzing studies with a low risk of bias or with a placebo control resulted in no difference in pain relief. In 22 trials that examined 3,404 patients for safety and tolerability, nonbenzodiazepine antispasmodics were more likely to cause an adverse event (relative risk = 1.6; 95% CI, 1.2 to 2.0) compared with control treatment, but were not less likely to be discontinued (relative risk = 1.5; 95% CI, 0.6 to 3.5). Antispasmodics and benzodiazepines produced no differences in pain intensity within two weeks or at weeks 3 through 13. There was significant heterogeneity among trial results for antispasmodics, with most of the benefit occurring in studies of the muscle relaxant thiocolchicoside, which is not marketed in the United States. There was no evidence of publication bias.

Study design: Meta-analysis (randomized controlled trials)

Funding source: Self-funded or unfunded

Setting: Various (meta-analysis)

Reference: Cashin AG, Folly T, Bagg MK, et al. Efficacy, acceptability, and safety of muscle relaxants for adults with non-specific low back pain: systematic review and meta-analysis. BMJ. 2021;374:n1446.

Editor's Note: Dr. Shaughnessy is an assistant medical editor for AFP.