Chlorzoxazone is a medication prescribed to relieve pain and stiffness resulting from muscle strains and sprains. MedlinePlus states that chlorzoxazone is commonly used in conjunction with pain relievers, rest and physical therapy.
Chlorzoxazone can cause side effects, including purple or red urine, upset stomach, dizziness, drowsiness, weakness and lightheadedness. MedlinePlus advises reporting these side effects to a physician only if they are severe or unrelieved. It is best for patients taking chlorzoxazone to avoid driving or operating heavy machinery until they know how the medication affects them. Serious side effects, including skin rash, itching, stomach pain and yellowing of the skin or eyes, should be reported to a doctor immediately.