Muscle relaxants (also called skeletal muscle relaxants) are a diverse group of medicines that have the ability to relax or reduce tension in muscle. Some (such as baclofen, methocarbamol, and tizanidine) work in the brain or spinal cord to block over-excited neuronal (nerve) pathways. Others (such as dantrolene and botulinum toxin) act directly on muscle. Cannabis extract is thought to have a dual effect.
Muscle relaxants treat two main conditions: spasticity (stiff, rigid muscles) caused by conditions such as cerebral palsy, multiple sclerosis, and stroke; or muscle spasms which are typically temporary and associated with conditions such as tension headache, low back pain, or fibromyalgia.
Only three muscle relaxants – baclofen, dantrolene, and tizanidine are FDA approved to treat spasticity; however, six (carisoprodol, chlorzoxazone, cyclobenzaprine, metaxalone, methocarbamol, and orphenadrine) are approved to treat muscle spasm. Botulinum toxin is only approved to treat spasticity in certain muscle groups of the upper and lower limbs. Many other medications are also used to treat spasticity or muscle spasm although most are not approved for this indication.
Evidence supporting the effectiveness of skeletal muscle relaxants for muscle spasm is sparse; most trials are old and not of good quality. For this reason, skeletal muscle relaxants should only be used to treat muscle spasm if other treatments fail.
