Generic name: cyclobenzaprine [ sye-kloe-BEN-za-preen ]
Brand names: Amrix, Comfort Pac with Cyclobenzaprine, Fexmid, Flexeril
Drug class: Skeletal muscle relaxants

Medically reviewed by Kaci Durbin, MD. Last updated on Aug 15, 2023.

What is cyclobenzaprine?

Cyclobenzaprine is a muscle relaxant. It works by blocking nerve impulses (or pain sensations) that are sent to your brain. Cyclobenzaprine is used together with rest and physical therapy to treat skeletal muscle conditions such as pain or injury.

Cyclobenzaprine may also be used for purposes not listed in this medication guide.

Warnings

You should not use cyclobenzaprine if you have an allergy to the medication, a certain type of thyroid disorder (hyperthyroidism), heart block, congestive heart failure, a heart rhythm disorder, or you have recently had a heart attack.

Do not use cyclobenzaprine if you have taken an MAO inhibitor in the past 14 days, such as isocarboxazid, linezolid, phenelzine, rasagiline, selegiline, or tranylcypromine.

Before taking this medicine

You should not use cyclobenzaprine if you are allergic to it, or if you have:

• hyperthyroidism;

• heart block, heart rhythm disorder, congestive heart failure; or

• if you have recently had a heart attack.

Cyclobenzaprine is not approved for use by anyone younger than 15 years old.

Do not use cyclobenzaprine if you have taken an MAO inhibitor in the past 14 days. A dangerous drug interaction could occur. MAO inhibitors include isocarboxazid, linezolid, phenelzine, rasagiline, selegiline, and tranylcypromine.

Some medicines can interact with cyclobenzaprine and cause a serious condition called serotonin syndrome. Be sure your doctor knows if you also take stimulant medicine, opioid medicine, herbal products, or medicine for depression, mental illness, Parkinson's disease, migraine headaches, serious infections, or prevention of nausea and vomiting. Ask your doctor before making any changes in how or when you take your medications.

To make sure cyclobenzaprine is safe for you, tell your doctor if you have:

• thyroid disease;

• liver disease;

• glaucoma;

• enlarged prostate; or

• problems with urination.

It is not known whether cyclobenzaprine will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant.

It may not be safe to breast-feed while using this medicine. Ask your doctor about any risk.

Older adults may be more sensitive to the effects of this medicine.

How should I take cyclobenzaprine?

Cyclobenzaprine is usually taken taken for up to 2 or 3 weeks. Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose.

Follow your doctor's dosing instructions very carefully.

Swallow the capsule whole and do not crush, chew, break, or open it.

Call your doctor if your symptoms do not improve after 3 weeks, or if they get worse.

Store at room temperature away from moisture, heat, and light.

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of cyclobenzaprine can be fatal.

Overdose symptoms may include severe drowsiness, vomiting, fast heartbeats, tremors, agitation, or hallucinations.

What to avoid

Avoid driving or hazardous activity until you know how this medicine will affect you. Your reactions could be impaired.

Avoid drinking alcohol. Dangerous side effects could occur.

Cyclobenzaprine side effects

Get emergency medical help if you have signs of an allergic reaction to cyclobenzaprine: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Stop using this medicine and call your doctor at once if you have:

• fast or irregular heartbeats;

• chest pain or pressure, pain spreading to your jaw or shoulder; or

• sudden numbness or weakness (especially on one side of the body), slurred speech, balance problems.

Seek medical attention right away if you have symptoms of serotonin syndrome, such as: agitation, hallucinations, fever, sweating, shivering, fast heart rate, muscle stiffness, twitching, loss of coordination, nausea, vomiting, or diarrhea.

Serious side effects may be more likely in older adults.

Common cyclobenzaprine side effects may include:

• drowsiness, tiredness;

• headache, dizziness;

• dry mouth; or

• upset stomach, nausea, constipation.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Related/similar drugs

What other drugs will affect cyclobenzaprine?

Using cyclobenzaprine with other drugs that make you drowsy can worsen this effect. Ask your doctor before using opioid medication, a sleeping pill, a muscle relaxer, or medicine for anxiety or seizures.

Tell your doctor about all your other medicines, especially:

• MAO inhibitors, such as isocarboxazid, linezolid, phenelzine, rasagiline, selegiline, or tranylcypromine;

• Any antidepressant or anxiety medications;

• bupropion (Zyban, for smoking cessation or Wellbutrin, for depression);

• meperidine;

• tramadol;

• verapamil;

• cold or allergy medicine that contains an antihistamine (Benadryl and others);

• medicine to treat Parkinson's disease;

• medicine to treat excess stomach acid, stomach ulcer, motion sickness, or irritable bowel syndrome;

• medicine to treat overactive bladder; or

• bronchodilator asthma medication.

This list is not complete. Other drugs may interact with cyclobenzaprine, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

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Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use cyclobenzaprine only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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