Treating low back pain with commonly prescribed muscle relaxants is ‘largely ineffective’, according to a new study.

Researchers in Australia conducted a review of literature published up to February 2021 to examine the efficacy, acceptability and safety of a number of different muscle relaxants. The findings have been published today (7 July) in the BMJ.

Evidence from 31 randomised controlled trials involving more than 6,500 participants with non-specific low back pain suggested that while the drugs may successfully treat short-term pain, the effect is ‘too small to be considered clinically meaningful’.

However, the certainty of evidence overall is low and larger trials must be conducted to establish more robust clinical recommendations, the researchers said.

The study looked at the effects on acute, chronic and mixed low back pain of the following, widely used muscle relaxants:

  • non-benzodiazepine antispasmodics (carisoprodol, cyclobenzaprine, metaxalone, methocarbamol, thiocolchicoside, tizanidine, tolperisone, orphenadrine)
  • antispastics (baclofen, dantrolene)
  • benzodiazepines (diazepam)
  • miscellaneous muscle relaxants (botulinum toxin, eszopiclone).

Researchers compared the effectiveness of the drugs with placebo, usual care and no treatment in adults with non-specific low back pain. The outcomes examined were pain intensity and satisfaction with the treatment, disability, adverse events, serious adverse events, and tolerability.

They found that muscle relaxants might reduce pain intensity at two weeks or less for patients with acute low back pain, compared with controls, but that the effect is minimal and not clinically meaningful.

There was little to no effect on pain intensity at three to 13 weeks, or on disability at all follow-up time points.

Moreover, the medications might induce side effects including dizziness, drowsiness, headache and nausea, and have little to no effect on treatment discontinuation compared with controls.

The authors said that although the pain-relieving effects were modest, they ‘could still mean that some, but not all, individuals gain a worthwhile benefit’.

‘We would encourage clinicians to discuss this uncertainty in the efficacy and safety of muscle relaxants with patients, sharing information about the possibility for a worthwhile benefit in pain reduction but increased risk of experiencing a non-serious adverse event, to allow them to make informed treatment decisions,’ they said.

‘Large, high-quality, placebo-controlled trials are urgently needed to resolve uncertainties about the efficacy and safety of muscle relaxants for low back pain.’