Common Risks and Side Effects of Muscle Relaxants

Muscle relaxants can be helpful in alleviating acute back pain, but patients should be aware of certain potential problems. For example, both carisoprodol and diazepam are classified by the U.S. Drug Enforcement Administration as Schedule IV controlled substances based on their potential for abuse and addiction.

See Lower Back Pain Symptoms and Diagnosis

To minimize risk, the doctor should be informed of any history of seizures, liver disease, myasthenia gravis, or epilepsy, and any other medical conditions or concerns. Women should inform their doctors if they are pregnant, plan to become pregnant, or are breast-feeding.

  • Potential for abuse
    Muscle relaxants are typically prescribed early in a course of back pain, on a short-term basis. One reason for the short time frame is the potential for dependence or abuse. Muscle relaxants should be kept in a place where visitors and children will not find them. It is illegal to share these medications with anyone else.
  • Interactions with antihistamines
    Combining muscle relaxants and antihistamines should be avoided. The combination has been linked to an increase in emergency room visits for older adults.1
  • Interactions with alcohol
    Drinking alcohol can be especially dangerous when taking muscle relaxants. The sedative effect of the medication is intensified with alcohol use, and combining the two can be fatal.
  • See Alcohol Avoidance

  • Allergic reactions
    No medication should be taken if the patient has had an allergic reaction to it in the past, even if the reaction seemed mild. Symptoms of an allergic reaction include swelling in the throat or extremities, trouble breathing, hives, and chest tightness.
  • Sleepiness
    Because muscle relaxers are a total body relaxant, they typically induce grogginess or sleepiness. As a result, it is not safe to drive or make important decisions while taking muscle relaxants. Muscle relaxants are often suggested for evening use due to their sedative effect. Timing is a consideration in taking muscle relaxants. If a muscle relaxant designed to last 12 hours is taken at 10 p.m., driving to work at 7 a.m. would not be advised. A more short-acting muscle relaxer may be better in certain situations.
  • Tapering off
    Stopping a muscle relaxant abruptly can be harmful. Instead, the doctor will prescribe a gradual reduction in dosage.

Other serious side effects include problems breathing, light-headedness or fainting, blurred vision, confusion, nausea, and urinary retention. The doctor should be notified immediately of any serious side effects.

Article continues below

Considerations During Pregnancy

The U.S. Food and Drug Administration has rated medications for safety during pregnancy on a scale of A through X for decades. This rating is being gradually replaced with more detailed information, but the ranking is still helpful as a quick reference for many existing medications.

See Management of Back Pain in Pregnancy

In This Article:

These are the categories:

  • A: Controlled human studies show no fetal risks; these drugs are the safest.
  • B: Animal studies show no risk to the fetus, but no controlled human studies have been conducted, or animal studies show a risk to the fetus, but well-controlled human studies do not.
  • C: No adequate animal or human studies have been conducted, or adverse fetal effects have been shown in animals, but no human data are available.
  • D: Evidence of human fetal risk exists, but benefits may outweigh risks in certain situations (e.g., life-threatening disorders, serious disorders for which safer drugs cannot be used or are ineffective).
  • X: Proven fetal risks outweigh any possible benefit.

The above is not a complete list of potential risks, complications and side effects; patients are advised to speak with their doctor and pharmacist regarding their individual prescription and health.


  1. Alvarez CA, Mortensen EM, Makris UE, et al. Association of skeletal muscle relaxers and antihistamines on mortality, hospitalizations, and emergency department visits in elderly patients: a nationwide retrospective cohort study. BMC Geriatrics. 2015;15:2. doi:10.1186/1471-2318-15-2.