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Overview: Chlorzoxazone is used short-term to relieve muscle, bone, and joint pain. It seems to relax muscles by affecting nerve activity in the spinal cord. Common side effects include dizziness and drowsiness. Do not drive or do other activities that require alertness or coordination until you know how chlorzoxazone affects you.

Uses

What is chlorzoxazone used for?

Chlorzoxazone is commonly used for discomfort related to short-term, painful musculoskeletal conditions. These are conditions that affect the muscles, bones, and joints of your body.

Chlorzoxazone may also be used for other conditions as determined by your healthcare provider.

How does chlorzoxazone work (mechanism of action)?

Chlorzoxazone works by reducing nerve activity in the spinal cord. This helps to relax the muscles and reduce muscle spasms.

How is chlorzoxazone supplied (dosage forms)?

Dosage forms and strengths

  • 250 mg, 375 mg, 500 mg, 750 mg oral tablets

How should I store chlorzoxazone?

Chlorzoxazone should be stored at room temperature, between 68 F to 77 F (20 C to 25 C). It can be exposed to temperatures between 59 F to 86 F (15 C to 30 C) for shorter periods of time, such as when transporting it. Store in a cool, dry place.

Side Effects

What are the most common side effects of chlorzoxazone?

The most common side effects of chlorzoxazone are listed below. Tell your healthcare provider if you have any of these side effects that bother you.

  • Stomach discomfort 
  • Drowsiness and dizziness
  • Lightheadedness
  • A general feeling of being unwell, tired, or not having your usual energy 

There may be other side effects of chlorzoxazone that are not listed here. Contact your healthcare provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088. In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of chlorzoxazone?

While less common, the most serious side effects of chlorzoxazone are described below, along with what to do if they happen.

Severe Allergic Reactions. Chlorzoxazone may cause allergic reactions, which can be serious. Stop taking chlorzoxazone and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Liver Damage. Liver damage, also called hepatotoxicity, can happen when taking chlorzoxazone. Call your healthcare provider right away if you have any of the following symptoms of liver damage.

  • Nausea or vomiting
  • Stomach or belly pain
  • Fever
  • Weakness or unusual tiredness
  • Itching
  • Loss of appetite
  • Light-colored poop
  • Dark-colored urine (pee)
  • Your skin or the whites of your eyes turning yellowish in color (also called jaundice) 

Stomach or Intestinal Bleeding. Chlorzoxazone can increase your risk of bleeding in your stomach and intestines. Call your healthcare provider right away if you have any of the following signs of bleeding while taking chlorzoxazone.

  • Nausea and vomiting
  • Vomit with blood that looks like coffee grounds
  • Coughing up blood or blood clots
  • Black or tarry poop
  • Stomach pain

Warnings & Precautions

Who should not use chlorzoxazone?

Allergies to Ingredients. People who are allergic to any of the following should not take chlorzoxazone.

  • Chlorzoxazone
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific chlorzoxazone products they stock.

What should I know about chlorzoxazone before using it?

Do not take chlorzoxazone unless it has been prescribed to you by a healthcare provider. Take it as prescribed.

Do not share chlorzoxazone with other people, even if they have the same condition as you. It may harm them.

Keep chlorzoxazone out of the reach of children.

Chlorzoxazone can affect your alertness or coordination. Do not drive or do other activities that require alertness or coordination until you know how chlorzoxazone affects you.

Chlorzoxazone is usually used with rest, physical therapy, or other measures to help with discomfort related to painful musculoskeletal conditions.

People who are 65 years and older can be at greater risk for some side effects of chlorzoxazone. Talk to your healthcare provider about your risks if you are in this age group.

What should I tell my healthcare provider before using chlorzoxazone?

Tell your healthcare provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them determine if chlorzoxazone is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions. Tell your healthcare provider if you have any of the following.

  • Liver problems
  • History of allergic reactions

Other Medicines and Supplements. Chlorzoxazone may interact with other medicines and supplements. Before taking chlorzoxazone, tell your healthcare provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. It is not known if or how chlorzoxazone could affect pregnancy or harm an unborn baby. Tell your healthcare provider if you are or plan to become pregnant.

Breastfeeding. It is not known if chlorzoxazone passes into breast milk. Tell your healthcare provider if you are breastfeeding or plan to breastfeed.

Interactions

Does chlorzoxazone interact with foods or drinks?

There are no known interactions between chlorzoxazone and foods or drinks.

The risk of drowsiness and dizziness may be increased if you drink alcohol while taking chlorzoxazone.

Does chlorzoxazone interact with other medicines (drug interactions)?

Always tell your healthcare provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following medicines before taking chlorzoxazone.

  • A muscle relaxant, such as carisoprodol (Soma), cyclobenzaprine, metaxalone, or tizanidine (Zanaflex)
  • Any other medicine that causes dizziness and sleepiness, such as prescription pain medicines, sleep medicines, and medicines for anxiety

This may not be a complete list of medicines that can interact with chlorzoxazone. Always check with your healthcare provider.

Does Chlorzoxazone (Paraflex, Parafon Forte) interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much chlorzoxazone?

If you or someone else has taken too much chlorzoxazone, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of chlorzoxazone?

If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses.