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Chlorzoxazone

Paraflex · ATC code M03BB03

Also known as: Chlorzoxazon, Klorzoksazon

Key facts
Active substance
Chlorzoxazone
Drug class
Muscle relaxant
ATC code
M03BB03
Authorisation
authorised nationally; no central EU authorisation
Information as of
2026-10-29

Key facts

Chlorzoxazone is, per the US prescribing information, a centrally acting agent used as an adjunct to rest and physical therapy for acute, painful musculoskeletal conditions.

What it is used for

  • Adjunct to rest, physical therapy and other measures for the relief of discomfort associated with acute, painful musculoskeletal conditions.
  • Its mode of action is not clearly identified but may be related to its sedative properties; it does not directly relax tense skeletal muscles.

Dosing

  • Usual adult dosage: one tablet (250 mg) three or four times daily.
  • Initial dosage for painful musculoskeletal conditions: two tablets (500 mg) three or four times daily; if the response is inadequate, up to three tablets (750 mg) three or four times daily.
  • As improvement occurs, the dosage can usually be reduced.

Contraindications

  • Known intolerance to the drug.

Important warnings

  • Serious (including fatal) hepatocellular toxicity has been reported rarely; the mechanism is unknown and unpredictable.
  • Stop immediately at early signs of liver injury (fever, rash, anorexia, nausea, vomiting, fatigue, right upper quadrant pain, dark urine, jaundice) or if liver enzymes become abnormal.
  • Caution in patients with known allergies; stop if a sensitivity reaction such as urticaria, redness or itching occurs.
  • Alcohol and other CNS depressants may have an additive effect.

Side effects

  • Occasional gastrointestinal disturbances; in rare instances possibly gastrointestinal bleeding.
  • Occasional drowsiness, dizziness, lightheadedness, malaise or overstimulation.
  • Rarely allergic skin rashes, petechiae or ecchymoses; angioneurotic edema or anaphylactic reactions are extremely rare.
  • Rarely discoloration of the urine from a metabolite, of no known clinical significance.

Interactions

  • Alcohol and other central nervous system depressants: possible additive effect.

Pregnancy and breastfeeding

  • Safe use with respect to fetal development has not been established; in women of childbearing potential use only when the potential benefits outweigh the possible risks.

Summary of the official product information, written with AI on 2026-10-29. Every number was checked automatically against the original text. Not reviewed by a physician – the full official text is authoritative.

Full official text →

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For patients

Patient information (US)

This product has no separate US patient information.

Authorisation and brand names by country

Medicines with exactly this active-substance composition, as listed in the national registers – alphabetical and without ranking. Whether a product is currently available is not shown here.

Turkey

  • ParaflexGÜREL İLAÇ TİC. A.Ş. · 4 register entries

Source: TİTCK – Ruhsatlı Beşeri Tıbbi Ürünler Listesi, as of 2026-10-16

Brand names in 5 more European countries
Bulgaria
Миоксазон
Denmark
Klorzoxazon Dak, Klorzoxazon Evolan
Hungary
Myoflexin
Romania
Clorzoxazonă Arena, Clorzoxazonă Richter
Sweden
Klorzoxazon Evolan, Klorzoxazon Orifarm, Paraflex

EMA – Article 57 product data (EU/EEA), 2026-10-29

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Sources

  1. U.S. Food and Drug Administration. CHLORZOXAZONE (Happy Robin, LLC) – Prescribing Information, 2025-10-08. DailyMed (NLM), 2026-10-29. https://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=3f90c7bc-118f-4371-e063-6394a90a279a
  2. TİTCK – Ruhsatlı Beşeri Tıbbi Ürünler Listesi, 2026-10-16. https://www.titck.gov.tr/dinamikmodul/85
  3. Wikidata (CC0): ATC M03BB.

Editorial: Medelix editorial team · last updated 2026-10-29 · How these pages are made · Report an error

Source: U.S. Food and Drug Administration (FDA), prescribing information, via DailyMed (NLM); public domain. Not advertising, not a treatment recommendation. For questions about your own treatment, ask your doctor or pharmacist.