Clinical data
Trade namesLorzone, Paraflex, Muscol
License data
Routes of
By mouth
Drug classSkeletal muscle relaxants
ATC code
Legal status
Legal status
Pharmacokinetic data
BioavailabilityWell absorbed
Protein binding13–18%
Elimination half-life1.1 hours
Duration of action3–4 hours
Excretionurine (<1%)
  • 5-chloro-3H-benzooxazol-2-one
CAS Number
PubChem CID
CompTox Dashboard (EPA)
ECHA InfoCard100.002.186 Edit this at Wikidata
Chemical and physical data
Molar mass169.56 g·mol−1
3D model (JSmol)
  • Clc2cc1c(OC(=O)N1)cc2
  • InChI=1S/C7H4ClNO2/c8-4-1-2-6-5(3-4)9-7(10)11-6/h1-3H,(H,9,10) checkY

Chlorzoxazone (INN) is a centrally acting muscle relaxant used to treat muscle spasm and the resulting pain or discomfort. It can also be administered for acute pain in general and for tension headache (muscle contraction headache). It acts on the spinal cord by depressing reflexes. It is sold under the brand names Lorzone, Paraflex and Muscol and in combination form as Parafon Forte, a combination of chlorzoxazone and acetaminophen (paracetamol). Possible side effects include dizziness, lightheadedness, malaise, nausea, vomiting, and liver dysfunction. When used with acetaminophen it has added risk of hepatotoxicity.[medical citation needed]

It is available as a generic medication.[3]

Like metaxalone, its mechanism of action is still in question. It is believed that metaxalone works by altering serotonin levels and acting as a mild MAO inhibitor.[medical citation needed] The mechanism of action of chlorzoxazone is thought[by whom?] to act on GABAA and GABAB receptors and voltage-gated calcium channels to a degree.[medical citation needed] General central nervous system depression is the only currently accepted aspect to its medical benefits.[medical citation needed] Elucidation of the exact mechanism of action is ongoing but there is limited study due to the existence of more effective, safe muscle relaxants (e.g., diazepam, cyclobenzaprine, tizanidine), greatly limiting the potential benefit of identifying novel compounds which share chlorzoxazone's mechanism of action.

See also


  1. ^ "Parafon DSC- chlorzoxazone tablet". DailyMed. 9 February 2010. Retrieved 5 November 2020.
  2. ^ "Lorzone- chlorzoxazone tablet". DailyMed. 21 June 2019. Retrieved 5 November 2020.
  3. ^ "Competitive Generic Therapy Approvals". U.S. Food and Drug Administration (FDA). 29 June 2023. Archived from the original on 29 June 2023. Retrieved 29 June 2023.

Further reading