Muscle relaxants for SMA

Last updated Jan. 21, 2025, by Andrea Lobo, PhD
Fact-checked by José Lopes, PhD

Muscle relaxants are medications that work to reduce muscle tension, stiffness, and spasms, thus easing pain and discomfort.

These medications may work in different ways, from acting on the central nervous system (brain and spinal cord) and slowing down activity to prevent the nerves from sending pain signals, to targeting the spinal cord or muscles to ease muscle tightness and involuntary spasms.

Muscle relaxants can be divided into two major categories: antispastics and antispasmodics. Antispastics address spasticity, an unusual tightness or stiffness of muscles, whereas antispasmodics are used to treat pain, particularly lower back pain, and muscle spasms.

Medications are available that can help people diagnosed with spinal muscular atrophy (SMA), and may be prescribed by a patient’s healthcare team as part of the individual’s care strategy.

How SMA affects muscles

SMA is mainly caused by mutations in the SMN1 gene, which provides instructions to produce the survival motor neuron, or SMN, protein. As this protein is key for the function and survival of motor neurons, the nerve cells that control voluntary movement, SMA results in their progressive degeneration and loss.

For muscles to move, nerve signals are sent from motor neurons in the brain and spinal cord to muscle cells. In SMA, as motor neurons die off, messages sent from the brain to the muscles are lost. Without signals from nerves, muscles of SMA patients weaken and shrink from inactivity.

SMA symptoms include muscle weakness and wasting, as well as spasticity — which can cause pain or discomfort and involuntary muscle contractions. Spasticity, which usually is caused by damage to nerve pathways controlling movement and stretch reflexes, can affect movement, as muscles remain contracted and resist being stretched.

Muscle relaxants in SMA

Muscle relaxants may be part of SMA treatment, as they can help decrease muscle spasms and spasticity. Examples include:

• Baclofen (sold as Lyvispah, Gablofen, among others; generics are available)
• Botulinum toxin A (including Botox, Xeomin, and Dysport)
• Tizanidine (sold as Ontralfy and Zanaflex; generics are available)
• Benzodiazepines (including alprazolam, diazepam, clonazepam, triazolam, and lorazepam).

Baclofen

Baclofen is approved by the U.S. Food and Drug Administration to treat spasticity and associated pain and rigidity in people with multiple sclerosis, spinal cord injury, or other spinal cord diseases.

This therapy is an analog (a similar molecule) of gamma-aminobutyric acid (GABA), a chemical messenger that decreases nerve cells’ likelihood of receiving, creating, or sending nerve signals. By binding to the GABA-B receptor protein, baclofen is able to treat muscle spasms and spasticity.

It can be taken orally or via direct injection into the spinal canal.

Botulinum toxin A

Botulinum toxin A products are used for therapeutic and cosmetic purposes. Although approved indications are specific to each therapy, they may include treatment of spasticity, overactive bladder and urinary incontinence, as well as headache in adults with chronic migraine.

This type of therapy contains a neurotoxin obtained from a bacterium called Clostridium botulinum, which prevents the release of a messenger called acetylcholine into the connections between nerves and muscle cells. Acetylcholine normally triggers muscle contraction and sweat secretion. As a result, botulinum toxin A helps relax muscles and provides pain relief.

These medications are injected locally into muscles.

Tizanidine

Tizanidine is a short-acting muscle relaxant approved to treat spasticity.

The medication works by activating alpha-2 adrenoceptors to inhibit the activity of motor neurons. This reduces the release of chemical messengers that make nerve cells more likely to fire electric impulses and drive the onset of muscle spasms.

As the therapy has a short-duration therapeutic effect, it should be reserved for daily activities or periods when spasticity relief is most important. It is given orally.

Benzodiazepines

Benzodiazepines are approved in the U.S. for several indications, including the treatment of anxiety, muscle spasms, seizures, and panic disorder (anxiety disorder characterized by sudden attacks of panic or fear). Different therapies may have different approved indications.

These therapies work to enhance the inhibitory effect of GABA to slow down activity in the brain and nervous system, making them effective for relieving anxiety, aiding with sleep, and easing spasms and spasticity due to their muscle-relaxing properties.

Benzodiazepines may be given orally, by injection, or as a rectal gel (to treat seizures).

Common side effects of muscle relaxants

The most common side effects of muscle relaxants reported in people treated for spasticity, but not due to SMA specifically, include:

• runny nose, sore throat
• upper respiratory infection
• fatigue, lack of energy
• spasticity
• dizziness
• drowsiness
• excessive drooling
• confusion
• depression
• gastrointestinal symptoms (nausea, vomiting, diarrhea, constipation)
• dry mouth
• amblyopia (lazy eye), blurred vision, and eyelid swelling
• abnormal blood pressure
• urinary tract infection, urinary incontinence, and urinary retention
• sleep problems (insomnia, somnolence)
• problems swallowing
• back pain, neck pain, pain in an extremity
• headache
• skin reactions
• nervousness
• speech disorder
• dyskinesia (involuntary, erratic, writhing movements)
• problems with coordination.

SMA News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.