Muscle relaxants are drugs that relax certain muscles in the body.
Strains, sprains, and other muscle injuries can result in pain, stiffness, and muscle spasms. Muscle relaxants do not heal the injuries, but they do help ease the discomfort and stop muscle spasms. The muscle relaxant cyclobenzaprine (Flexeril) is also sometimes used to treat fibromyalgia, a condition that involves aches, stiffness, and fatigue.
Muscle relaxants work by acting on the central nervous system. In the United States, they are available only with a physician's prescription. Some muscle relaxants are available in Canada without a prescription. Most come only in tablet form. However, methocarbamol (Robaxin) is available in both tablet and injectable forms. Examples of muscle relaxants are carisoprodol (Soma), chlorzoxazone (Parafon Forte DSC), cyclobenzaprine (Flexeril), and methocarbamol (Robaxin).
Recommended dosage depends on the patient and the type of drug. Check with the physician who prescribed the drug or the pharmacist who filled the prescription for the correct dosage. Always take muscle relaxants exactly as directed by your physician. Never take larger or more frequent doses, and do not take the drug for longer than directed.
Muscle relaxants are usually prescribed along with rest, exercise, physical therapy, or other treatments. Although the drugs may provide relief, they should never be considered a substitute for these other forms of treatment. The drugs may make the injury feel so much better that one is tempted to go back to normal activity, but doing too much too soon can actually make the injury worse.
These drugs work quite well for relieving muscle pain due to injuries, but are not effective for other types of pain. They should not be used for any other purpose other than for what they were prescribed.
Some people feel drowsy, dizzy, confused, lightheaded, or less alert when using these drugs. The drugs may also cause blurred vision, clumsiness, or unsteadiness. For these reasons, anyone who takes these drugs should not drive, operate machinery, or do anything else that might be dangerous until they have found out how the drugs affect them.
Because muscle relaxants work on the central nervous system, they may add to the effects of alcohol and other drugs that slow down the central nervous system, such as antihistamines, cold medicine, allergy medicine, sleep aids, medicine for seizures, tranquilizers, some pain relievers, and other muscle relaxants. They may also add to the effects of anesthetics, including those used for dental procedures. Anyone taking muscle relaxants should check with his or her physician before taking any of the above.
Persons with diabetes should be aware that the metaxalone (Skelaxin) may cause false test results on one type of test for sugar in the urine.
People with certain medical conditions or who are taking certain other medicines can have problems if they take muscle relaxants. Before taking these drugs, be sure to let the physician know about any of these conditions:
Anyone who has had unusual reactions to muscle relaxants in the past should let his or her physician know before taking the drugs again. The physician should also be told about any allergies to foods, dyes, preservatives, or other substances.
One muscle relaxant, carisoprodol (Soma), passes into breast milk and may make nursing babies drowsy or upset their stomachs. Whether other muscle relaxants pass into breast milk is unknown, but no evidence exists that they cause problems in nursing babies whose mothers take them. However, the physician should know whether any woman is pregnant or planning to get pregnant before she receives a prescription for this class of drugs.
Other medical conditions
Before using muscle relaxants, people with any of these medical problems should make sure their physicians are aware of their conditions:
- Kidney disease
- Heart or blood vessel disease or recent heart attack
- Irregular heartbeat
- Overactive thyroid gland
- Hepatitis or other liver disease
- Current or past alcohol or drug abuse
- Current or past blood disease caused by an allergy or a reaction to another drug
- Problems with urination.
In addition, people with epilepsy should be aware that taking the muscle relaxant methocarbamol may increase the likelihood of seizures.
Use of certain medicines
Taking muscle relaxants with certain other drugs may affect the way the drugs work or may increase the chance of side effects.
The most common side effects are vision changes, such as double vision or blurred vision; dizziness; lightheadedness; drowsiness; and dry mouth. These problems usually go away as the body adjusts to the drug and do not require medical treatment. If dry mouth is bothersome, suck on sugarless hard candy or ice chips, chew sugarless gum, or use saliva substitutes, which come in liquid and tablet forms. Less common side effects, such as stomach cramps or pain, nausea and vomiting, constipation, diarrhea, hiccups, clumsiness or unsteadiness, confusion, nervousness, restlessness, irritability, flushed or red face, headache, heartburn, weakness, trembling, and sleep problems, also may occur and do not need medical attention unless they do not go away or they interfere with normal activities.
Methocarbamol and chlorzoxazone may cause harmless color changes in urine --orange or reddish-purple with chlorzoxazone and purple, brown, or green with methocarbamol. The urine will return to its normal color when the patient stops taking the medicine.
More serious side effects are not common, but may occur. If any of the following side effects occur, check with the physician who prescribed the medicine as soon as possible:
- Breathing problems
- Swelling of the face
- Unusually fast or unusually slow heartbeat
- Tightness in the chest
- Rash, itching, hives, or redness
- Burning, stinging, red, or bloodshot eyes
- Stuffy nose
- Unusual thoughts or dreams.
The muscle relaxant chlorzoxazone (Parafon Forte DSC) has caused serious, life-threatening liver problems in some people. The reaction is rare, but anyone taking the drug should stop taking it and notify his or her physician immediately if any of these symptoms occur:
- Loss of appetite
- Pain in the upper right part of the abdomen
- Dark urine
- Yellow skin or eyes.
Additional, rare side effects may occur with any muscle relaxants. Anyone who has unusual symptoms after taking these drugs should get in touch with his or her physician.
Muscle relaxants may interact with some other medicines. When this happens, the effects of one or both of the drugs may change or the risk of side effects may be greater. Anyone who plans to take muscle relaxants should let the physician know all other medicines he or she is taking. Among the drugs that may interact with muscle relaxants are:
- Central nervous system (CNS) depressants, such as antihistamines, tranquilizers, sedatives, sleep aids, some pain relievers, cold medicines, allergy medicines, and medicines for seizures.
- Tricyclic antidepressants, such as amitriptyline (Elavil), imipramine (Tofranil), and desipramine (Norpramin).
- Monoamine oxidase inhibitors (MAO), such as phenelzine (Nardil) or tranylcypromine (Parnate). Serious, life-threatening reactions are possible in patients who take the muscle relaxant cyclobenzaprine (Flexeril) within two weeks of taking MAO inhibitors.
- Antispasmodic drugs, such as belladonna alkaloids and phenobarbital (Donnatal) or dicyclomine (Bentyl)
- Barbiturates, such as phenobarbital
- High blood pressure drugs, that contain guanethidine such as Esimil or Ismelin.
- Medicine that causes a loss of feeling, especially pain. Some anesthetics also cause a loss of consciousness.
- Medicine that prevents or relieves allergy symptoms
- Central nervous system
- The brain and spinal cord
- Medicine used to treat nervousness or restlessness
- Sudden, involuntary tensing of a muscle or a group of muscles
- Medicine that has a calming effect and is used to treat anxiety and mental tension
Gale Encyclopedia of Medicine. Gale Research, 1999.