Researchers in Australia found that muscle relaxants might reduce pain in the short term, but the effect is too small to be clinically meaningful, and there is a risk of adverse effects.
Reporting the findings of their meta-analysis in the BMJ, the researchers say that the certainty of evidence is low and large trials are needed to resolve uncertainties around the use of these drugs for back pain.
The team investigated the effectiveness, acceptability, and safety of muscle relaxants compared with placebo, usual care, or no treatment in adults with non-specific low back pain. Their analysis included data from 31 randomised controlled trials involving 6505 participants, published up to February 2021.
Very low certainty evidence showed that non-benzodiazepine antispasmodic drugs might reduce pain intensity at two weeks or less for patients with acute low back pain compared with controls. But this effect amounted to less than 8 points on a 0-100 point scale - less than the 10-point threshold considered to be clinically meaningful.
Non-benzodiazepine antispasmodics had little or no effect on pain intensity at 3-13 weeks or on disability at all follow-up time points.
Low and very low certainty evidence also showed that non-benzodiazepine antispasmodics might increase the risk of adverse events (such as dizziness, drowsiness, headache and nausea) and might have little to no effect on treatment discontinuation compared with controls.
No trials evaluated the effect of muscle relaxants on long-term outcomes.
The researchers acknowledge the modest overall effect they found could still mean that some individuals gain a worthwhile benefit from the drugs. However, they emphasise that the low to very low certainty of evidence does not allow any firm recommendations.
'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 say.
'Large, high quality, placebo controlled trials are urgently needed to resolve uncertainties about the efficacy and safety of muscle relaxants for low back pain,' they add.