Chlorzoxazone is a centrally acting muscle relaxant

Muscle relaxant

A muscle relaxant is a drug which affects skeletal muscle function and decreases the muscle tone. It may be used to alleviate symptoms such as muscle spasms, pain, and hyperreflexia. The term "muscle relaxant" is used to refer to two major therapeutic groups: neuromuscular blockers and spasmolytics...

 used to treat muscle spasm

Spasm

In medicine a spasm is a sudden, involuntary contraction of a muscle, a group of muscles, or a hollow organ, or a similarly sudden contraction of an orifice. It is sometimes accompanied by a sudden burst of pain, but is usually harmless and ceases after a few minutes...

 and the resulting pain or discomfort. It acts on the spinal cord by depressing reflexes. It is sold as Muscol or Parafon Forte, a combination of chlorzoxazone and acetaminophen (Paracetamol). Possible side effects include dizziness

Dizziness

Dizziness refers to an impairment in spatial perception and stability. The term is somewhat imprecise. It can be used to mean vertigo, presyncope, disequilibrium, or a non-specific feeling such as giddiness or foolishness....

, lightheadedness

Lightheadedness

Light-headedness is a common and often unpleasant sensation of dizziness and/or feeling that one may be about to faint, which may be transient, recurrent, or occasionally chronic. In some cases, the individual may feel as though his or her head is weightless. The individual may also feel as...

, malaise

Malaise

Malaise is a feeling of general discomfort or uneasiness, of being "out of sorts", often the first indication of an infection or other disease. Malaise is often defined in medicinal research as a "general feeling of being unwell"...

, nausea

Nausea

Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...

, vomiting

Vomiting

Vomiting is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose...

, and liver dysfunction. Used with acetaminophen it has added risk of hepatoxicity, which is why the combination is not recommended.
For a more in depth look at Chlorzoxazone visit http://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=15262.

Chemistry

Chlorzoxazone, 5-chloro-2-benzoxazolione, is synthesized by a hetercyclization reaction of 2-amino-4-chlorphenol with phosgene

Phosgene

Phosgene is the chemical compound with the formula COCl2. This colorless gas gained infamy as a chemical weapon during World War I. It is also a valued industrial reagent and building block in synthesis of pharmaceuticals and other organic compounds. In low concentrations, its odor resembles...

.

• D.F. Marsh, (1959).