Uses, Types, and Side Effects

Uses, Types, and Side Effects

Muscle relaxers are a group of medications that relax and reduce muscle tension (spasms). They also help decrease the pain associated with stiff and rigid muscles (spasticity). Muscle relaxers are useful for managing medical conditions that cause muscle stiffness and preventing the movement of muscles during surgery. 

Muscle relaxers are prescription medications available in oral or injectable forms. While the relaxers are typically tolerable for most people, their use may require strict medical supervision due to the associated possible risks.

There are two ways muscle relaxers can relax muscles. Some muscle relaxers block the transmission of nerve signals in the brain or spinal cord so the signals can’t be sent to the muscle. Other muscle relaxers target the muscle fibers directly so that the muscles relax.

Muscle relaxers can relax either smooth muscles or skeletal muscles: 

  • Smooth muscle relaxers: Act on smooth muscles— muscles you can’t voluntarily control that are found in internal organs like your intestines as well as in blood vessels
  • Skeletal muscle relaxers: Act on skeletal muscles—muscles you use to move, such as the muscles in your legs and arms

Healthcare providers such as primary care physicians, neurologists, and pain specialists may prescribe muscle relaxers to treat various conditions that cause muscle stiffness and pain. These conditions can include musculoskeletal disorders (injuries or disorders that can affect your muscles) and neurological conditions (conditions that affect your nervous system, including your brain, spinal cord, and nerves).

In musculoskeletal disorders, like muscle spasms and lower back pain, muscle relaxers act directly on the muscles or in the brain to reduce muscle stiffness and pain.

In neurological conditions that can cause muscle stiffness, such as cerebral palsy, multiple sclerosis, and spinal cord injuries, muscle relaxers act in the brain to decrease muscle rigidity.

There are two major classes of muscle relaxers: antispastics and antispasmodics. The two differ based on how they work.


Antispastics are muscle relaxers that act directly on the spinal cord or skeletal muscles. Healthcare providers typically prescribe antispastics for brain and spinal cord injuries that cause muscle spasms or stiffness (spasticity).

These types of injuries can cause muscles to lose their interaction between the brain and spinal cord. The lost interaction causes some nerves to become hyperstimulated, leading to muscle rigidity. Muscle relaxers that act on the spinal cord block or inhibit the effects of these hyperstimulated nerves. The drugs reduce muscle tension and stiffness, which relaxes muscles and decreases pain associated with muscular rigidity and tightness.

Common antispastics include Lioresal (baclofen) and Dantrium (dantrolene). Lioresal can reduce muscle pain, stiffness, and tightness from multiple sclerosis, spinal cord injuries, or other spinal cord diseases. Dantrium can reduce muscle stiffness, tightness, and spasms associated with spinal cord injuries, stroke, multiple sclerosis, or cerebral palsy.

The drugs may not be suitable for everyone. For example, since using dantrolene may pose a higher risk of liver damage in some people, providers may choose to limit its use in people at higher risk for liver disease.


Antispasmodics work in the brain, altering the transmission of nerve signals between brain neurons. These altered nerve signals block the nerve signals from the brain to the muscles, managing muscle spasms.

There are two types of antispasmodics: benzodiazepines and non-benzodiazepines. 

Benzodiazepines block the activity of a specific brain neurotransmitter called gamma-aminobutyric acid (GABA). They may help with acute lower back pain. 

A common benzodiazepine is Valium (diazepam). Valium can help if you are unable to move parts of your body (paraplegia) or have abnormal muscle contractions (athetosis). The muscle relaxant can also help manage stiff-person syndrome, cerebral palsy, and other neurological disorders that cause muscle rigidity. Besides its muscle-relaxing effects, Valium might also be prescribed to manage anxiety disorders and seizures.

Non-benzodiazepines can act on both the brain and spinal cord. They are used in the short term—along with rest and physical therapy—for strains, sprains, and other muscle injuries. Non-benzodiazepines include:

  • Soma (carisoprodol)
  • Flexeril (cyclobenzaprine)
  • Skelaxin (metaxalone)
  • Robaxin (methocarbamol)
  • Norflex (orphenadrine) 

Muscle relaxers come in different forms. They are available as tablets, capsules, liquid solutions, or injections. The injections can be administered intravenously (through a vein) or intramuscularly (through a muscle).

For instance, carisoprodol, cyclobenzaprine, and metaxalone are commonly available in oral forms, while diazepam is available in both oral and injection formulations.

The severity of the symptoms or medical condition and individual preferences can influence the form you take. Healthcare providers typically prescribe oral tablets or capsules because they are easier to administer. However, injections are preferable for severe cases. 

How long it takes for muscle relaxers to work can vary depending on factors such as the type of muscle relaxant and whether it was taken as an oral or injectable.

Generally, muscle relaxers can cause the following side effects:

  • Drowsiness
  • Fatigue
  • Dry mouth
  • Dizziness
  • Nausea
  • Headache 

The specific side effects may vary based on each type of muscle relaxer. For example, here are some side effects that have been linked to certain types of muscle relaxers:


This muscle relaxant acts in the brain and spinal cord. Its common side effects include:

  • Weakness
  • Dizziness
  • Drowsiness
  • Vertigo
  • Insomnia


This is an antispasmodic that acts in the brain. Common side effects include dizziness, drowsiness, nausea, and vomiting. Rare but serious effects include:

  • Hemolytic anemia (low red blood cell count because the cells are destroyed faster than they can be replaced)
  • Low white cell count
  • Jaundice (yellowing of the skin and eyes) 


This is both an antispasmodic and antispastic muscle relaxer. Side effects include:

  • Drowsiness
  • Fatigue
  • Ataxia (lack of muscle coordination)


This is another antispasmodic muscle relaxer. Its potential side effects include:

  • Drowsiness
  • Dizziness
  • Headaches
  • Excessive sleepiness
  • Seizure

When taking muscle relaxers, consider their risks. For example, prolonged use of some muscle relaxers, such as carisoprodol and diazepam, increases the risk of dependence and abuse.

You should especially speak to your healthcare provider about the potential risks of muscle relaxers if any of the following pertains to you:

  • You take other medications: Some medications might interact with muscle relaxers. This includes opioids, which slow brain activity. Because muscle relaxers like diazepam can also slow brain functions, especially at higher doses, taking the two medications together could cause serious complications like central nervous system depression (when your brain and spinal cord activity slows down too much). 
  • You have a chronic medical condition: Intake of muscle relaxers in people with pre-existing chronic medical conditions, such as chronic liver and kidney diseases, requires caution. These chronic disorders can increase the risk of developing adverse drug effects.
  • You are pregnant or older: Certain muscle relaxers may be unsafe for these groups, or the safety risk may be unknown. If you need a muscle relaxer, discuss your safest options with your healthcare provider.

You should also take precautions when using muscle relaxers. The dizzying or sedative effects of most muscle relaxers can affect your level of mental alertness. Therefore, performing certain tasks after use may not be feasible for some people. Instead, you’ll want to wait to perform those tasks until the drug’s effect has worn off.

When taking muscle relaxers, contact your healthcare provider with any concerns or if you notice any of the following:

  • Worsening side effects
  • Persistent muscle spasms or pains
  • Risk of multidrug interactions
  • Presence of allergic reactions such as rash, itching, or facial swelling

Some allergic reactions are life-threatening and may warrant emergency care. Thus, seeking immediate, proper medical attention when you notice them is important.

Muscle relaxers are a group of medications that can help manage muscle spasms and spasticity and their associated symptoms, like pain. The medications can be used to treat conditions that affect muscles, such as cerebral palsy, spinal cord injuries, and lower back pain.

There are different types of muscle relaxers. Antispastics act on the spinal cord or directly on muscles, while antispasmodics influence nerve signals in the brain. Depending on the type, the relaxers are available in oral or injectable forms. 

Common side effects of muscle relaxers include drowsiness, fatigue, dry mouth, dizziness, nausea, and headache. If prescribed muscle relaxers, follow your provider’s instructions and seek medical assistance if you notice any significant changes.

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