Chlorzoxazone has not been shown to be any more effective than...
Chlorzoxazone was first sold in the United States in August 1958. The drug is approved by the FDA in addition to rest, physical therapy, and other measures for the relief of discomfort associated with acute, painful musculoskeletal conditions. The way chlorzoxazone works has not been clearly identified but may be related to its sedative properties. Chlorzoxazone does not directly relax tense skeletal muscles in people.
Chlorzoxazone has not been shown to be any more effective than painkillers or anti-inflammatory drugs such as aspirin for relieving the pain of local muscle spasm.
Some people taking chlorzoxazone have experienced drowsiness, headache, upset stomach, nausea, vomiting, heartburn, constipation, diarrhea, and loss of appetite as side effects.
Serious, sometimes fatal, liver toxicity has been reported in patients taking chlorzoxazone. The way chlorzoxazone causes liver toxicity is unknown but appears to be idiosyncratic and unpredictable. You should stop taking chlorzoxazone and contact your physician immediately if you develop the symptoms of liver toxicity, such as fever, rash, loss of appetite, nausea, vomiting, fatigue, abdominal pain, dark urine, or jaundice (yellowing of the skin or eyes).
The use of chlorzoxazone together with alcohol or other central nervous system depressants may have an additive sedative effect.