A systematic review examined the long-term use of skeletal muscle relaxants for chronic pain, finding limited evidence of benefit for most conditions.
In the review, published in JAMA Network Open, investigators examined 44 studies: 30 randomized clinical trials (RCTs) with 1,314 participants and 14 cohort studies with 1,168 participants, totaling 2,482 participants. They evaluated nine different skeletal muscle relaxants (SMRs) used for at least 1 month to treat various chronic pain syndromes.
Evidence was strongest for SMR efficacy in treating muscle spasms, painful cramps, and neck pain. SMRs showed little to no benefit compared with placebo for fibromyalgia, low back pain, and headaches.
For fibromyalgia, five studies examined cyclobenzaprine, three examined tizanidine, and one each examined chlormezanone, eperisone, and carisoprodol. Cyclobenzaprine improved sleep disturbance but not other outcomes compared with placebo. Tizanidine showed improvements in pain intensity from baseline in cohort studies.
In osteoarthritis studies, chlormezanone reduced sleep disturbances in neck osteoarthritis but not in other joints. Eperisone improved neck pain compared with placebo at 6 weeks.
The investigators systematically searched Ovid MEDLINE, Embase, Web of Science, CINAHL, and Cochrane databases through December 4, 2023. They included articles published in English, Spanish, and Italian, focusing on studies examining SMR use for at least 1 month for chronic pain.
The studies were categorized by pain syndrome: low back pain (5 studies), fibromyalgia (11 studies), headaches/trigeminal neuralgia (10 studies), painful cramps/spasticity (10 studies), and other syndromes (8 studies).
The most commonly studied SMRs were baclofen (11 studies, 25%), tizanidine (8 studies, 18%), and cyclobenzaprine (7 studies, 16%). Other medications included eperisone, quinine, carisoprodol, orphenadrine, chlormezanone, and methocarbamol.
Of the studies, 30% lasted 4 weeks, 56% lasted 4 to 12 weeks, and 16% lasted more than 12 weeks.
Quality assessment revealed a low to moderate risk of bias for RCTs and fair to good quality for cohort studies. Common issues included a lack of blinding in RCTs and low comparability of cohorts in observational studies.
The review noted that SMR prescribing doubled between 2005 and 2016, with physician visits for continuing SMR prescriptions tripling during the same period. Approximately 30% of the patients using opioids were also prescribed SMRs, increasing the risk of opioid-related overdose, particularly with longer use.
Limitations included restricting the review to English, Spanish, and Italian publications and the inability to conduct meta-analyses because of study heterogeneity.
The authors declared no competing interests.
