Patient-friendly summary
If you read nothing else
Bottom line
Long-term muscle relaxant use appears beneficial only for a small subset of pain conditions (cramps, spasms, neck pain); for fibromyalgia, low back pain, and headaches it did not appear better than placebo, and clinicians should weigh side effects and consider deprescribing if pain goals are not met.
Moderate evidencePublished
Evidence hierarchy
Study participants
Adults with chronic pain (3 months or longer) treated with a skeletal muscle relaxant for at least 4 weeks, across low back pain, fibromyalgia, headaches/trigeminal neuralgia, painful cramps or spasticity, and other syndromes
Study Summary
This systematic review evaluated the effectiveness and safety of long-term (4 weeks or longer) use of skeletal muscle relaxants (SMRs) for chronic pain, pooling 44 studies (30 randomized clinical trials and 14 cohort studies) with 2482 total participants and 9 unique medications. Evidence was strongest for SMRs used for trigeminal neuralgia, neck pain, and painful muscle cramps or spasms, where they may be more beneficial than placebo; for fibromyalgia, low back pain, headaches, and other syndromes, SMRs did not appear to be more beneficial than placebo. Most included studies were short (4-6 weeks), and the most common adverse effects were sedation and dry mouth. The authors conclude that clinicians should be vigilant for adverse effects and consider deprescribing when pain-related goals are not met.
Key Findings
| Finding | Detail | Impact |
|---|---|---|
| Muscle relaxants may help certain pain syndromes but not others | Evidence for effectiveness was strongest for SMRs used for trigeminal neuralgia, neck pain, and painful muscle cramps or spasms; evidence suggested SMRs for fibromyalgia, low back pain, headaches, and other syndromes were not more beneficial than placebo. | High |
| Most studies were short-term, limiting conclusions about true long-term use | Despite the focus on long-term use (4 weeks or longer), studies were primarily short-term (4-6 weeks). The authors note this short duration may bias toward higher apparent efficacy and lower observed adverse effects, since some pharmacologic pain treatments lose efficacy and accrue harms over time. | High |
| Sedation and dry mouth were the most common adverse effects | The most common adverse effects across studies were sedation and other central nervous system effects (including dizziness) and dry mouth. In one tizanidine study, 25% of participants dropped out due to adverse effects. | Medium |
| Nine muscle relaxants were studied, led by baclofen, tizanidine, and cyclobenzaprine | Eleven studies (25%) examined baclofen, 8 (18%) examined tizanidine, and 7 (16%) examined cyclobenzaprine; others examined eperisone, quinine, carisoprodol, orphenadrine, chlormezanone, and methocarbamol. | Medium |
| For fibromyalgia, cyclobenzaprine improved sleep but not other outcomes | In RCTs, cyclobenzaprine was associated with improvement in sleep disturbance but showed no difference from placebo on other outcomes; in one RCT comparing cyclobenzaprine with amitriptyline, both groups improved over 6 months with no difference between them. | Medium |
| Authors recommend considering deprescribing | Given limited evidence of long-term efficacy alongside growing prescriptions and known risks (including increased opioid-related overdose risk when combined with opioids), the authors suggest clinicians consider shared decision-making about deprescribing SMRs if pain-related goals are not met, especially in older patients. | High |
Evidence for effectiveness was strongest for SMRs used for trigeminal neuralgia, neck pain, and painful muscle cramps or spasms; evidence suggested SMRs for fibromyalgia, low back pain, headaches, and other syndromes were not more beneficial than placebo.
Despite the focus on long-term use (4 weeks or longer), studies were primarily short-term (4-6 weeks). The authors note this short duration may bias toward higher apparent efficacy and lower observed adverse effects, since some pharmacologic pain treatments lose efficacy and accrue harms over time.
The most common adverse effects across studies were sedation and other central nervous system effects (including dizziness) and dry mouth. In one tizanidine study, 25% of participants dropped out due to adverse effects.
Eleven studies (25%) examined baclofen, 8 (18%) examined tizanidine, and 7 (16%) examined cyclobenzaprine; others examined eperisone, quinine, carisoprodol, orphenadrine, chlormezanone, and methocarbamol.
In RCTs, cyclobenzaprine was associated with improvement in sleep disturbance but showed no difference from placebo on other outcomes; in one RCT comparing cyclobenzaprine with amitriptyline, both groups improved over 6 months with no difference between them.
Given limited evidence of long-term efficacy alongside growing prescriptions and known risks (including increased opioid-related overdose risk when combined with opioids), the authors suggest clinicians consider shared decision-making about deprescribing SMRs if pain-related goals are not met, especially in older patients.
Strengths
- Comprehensive search of five major databases (Ovid MEDLINE, Embase, Web of Science, CINAHL, Cochrane) through December 2023, plus grey literature, with no date restriction
- Broader scope than prior reviews, spanning multiple chronic pain syndromes and 9 medications rather than a single drug or condition
- Dual independent screening, data abstraction, and risk-of-bias assessment using validated tools (Cochrane Risk of Bias; Newcastle-Ottawa)
- PRISMA-guided and PROSPERO-registered with an a priori protocol
- RCTs had low to moderate risk of bias and cohort studies were of fair to good quality
Limitations
- Most included studies were short-term (4-6 weeks), so true long-term effectiveness and harms remain poorly characterized
- Heterogeneity in clinical settings, pain definitions, medications, and treatment durations precluded meta-analysis; only a narrative synthesis was possible
- Limited to studies published in English, Spanish, or Italian, potentially excluding research from low- and middle-income countries
- Only quantitative studies were included, omitting qualitative evidence on patient experiences
- No studies measured misuse of muscle relaxants, and many compared SMRs only with placebo or historical controls rather than active effective therapies
Key Takeaways for Patients
What This Means for You
- 01Muscle relaxants taken long-term may help with painful muscle cramps or spasms and with neck pain, but the evidence did not show a clear benefit for fibromyalgia, low back pain, or headaches.
- 02Most of the studies reviewed lasted only about a month, so there is little solid evidence on what happens when these medicines are taken for much longer.
- 03The most common side effects were feeling sleepy or drowsy, dizziness, and dry mouth.
- 04If you have been taking a muscle relaxant for a long time and your pain goals are not being met, it is worth discussing with your clinician whether to gradually stop it.
- 05For some conditions like low back pain and fibromyalgia, other treatments such as exercise, rehabilitation, and certain non-opioid medications have stronger evidence and may be better options to discuss.