Strains, sprains, and other muscle injuries can result in pain, stiffness, and muscle spasms. Muscle relaxants do not heal the injuries, but they do relax muscles and help ease 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. Examples of muscle relaxants are carisoprodol (Soma), chlorzoxazone (Parafon Forte DSC), cyclobenzaprine (Flexeril), and methocarbamol (Robaxin). Most come only in tablet form. However, methocarbamol (Robaxin) is available in both tablet and injectable forms. Some muscle relaxants are available in Canada without a prescription.

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...