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Pronunciationklor zox' a zone[1]
Trade namesLorzone, Paraflex, Muscol, others
  • 5-chloro-3H-benzooxazol-2-one
Clinical data
Drug classMuscle relaxant[1]
Main usesLow back pain, muscle spasms[1]
Side effectsDizziness, sleepiness, headache, tremor[1]
  • US: N (Not classified yet)
Routes of
By mouth
Onset of actionWith 1 hr[2]
Duration of actionUp to 4 hr[2]
External links
License data
Legal status
BioavailabilityWell absorbed
Protein binding13–18%
Elimination half-life1.1 hr
ExcretionUrine (<1%)
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, sold under the brand names Lorzone among others, is a muscle relaxant used to treat low back pain and muscle spasms.[1] Benefits are moderate.[1] It is not useful for neurological problems such as cerebral palsy.[2] It is taken by mouth.[1] Effects begin within an hour and last for up to 4 hours.[2]

Common side effects include dizziness, sleepiness, headache, and tremor.[1] Other side effects may include liver problems and angioedema.[1][2] Safety in pregnancy is unclear.[2] It works at the level of the spinal cord and brain.[2]

Chlorzoxazone was approved for medical use in the United States in 1958.[1] It is available as a generic medication.[1] In the United States 60 pills of 500 mg costs about 18 USD as of 2022.[5] As of 2017 it remains widely used.[1]

Medical uses


The usual recommended dose in adults is 250 to 750 mg by mouth three to four times daily, reducing the dose to lowest effective level once a response occurs.[1] It is typically given for 1 to 4 weeks only.[1]

See also


  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 "Chlorzoxazone". Archived from the original on 8 May 2021. Retrieved 4 January 2022.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 "Chlorzoxazone Monograph for Professionals". Archived from the original on 28 November 2021. Retrieved 4 January 2022.
  3. "Parafon DSC- chlorzoxazone tablet". DailyMed. 9 February 2010. Archived from the original on 16 March 2021. Retrieved 5 November 2020.
  4. "Lorzone- chlorzoxazone tablet". DailyMed. 21 June 2019. Archived from the original on 12 November 2020. Retrieved 5 November 2020.
  5. "Chlorzoxazone Prices, Coupons & Savings Tips - GoodRx". GoodRx. Archived from the original on 5 November 2016. Retrieved 4 January 2022.

Further reading

External links

External sites: