What Is Cyclobenzaprine (Flexeril and Amrix)?

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Cyclobenzaprine, the generic form of the brand-name drugs Flexeril and Amrix, is a muscle relaxer that relieves pain and discomfort caused by strains, sprains, and other muscle injuries.

It's also available under the brand names Fexmid and FusePaq Tabradol.

This medication is often part of an overall recovery plan that includes rest and physical therapy. Cyclobenzaprine is also prescribed off-label to treat fibromyalgia.

Cyclobenzaprine works on the central nervous system, blocking nerve impulses (or pain sensations) that are sent from sore muscles to your brain. Cyclobenzaprine is chemically related to a class of antidepressants called tricyclic antidepressants.

Cyclobenzaprine was first approved by the Food and Drug Administration (FDA) in 1977 under the brand name Flexeril, which is currently manufactured by PD-RX Pharmaceuticals.

Cyclobenzaprine Warnings

Don't take cyclobenzaprine if you've taken a monoamine oxidase inhibitor (MAOI) in the last two weeks. MAOIs, used to treat depression and Parkinson's disease, include:

  • Isocarboxazid (Marplan)
  • Linezolid (Zyvox)
  • Phenelzine (Nardil)
  • Rasagiline (Azilect)
  • Selegiline (Emsam)
  • Tranylcypromine (Parnate)


Do not take this drug if you have a history of heart problems, including a previous heart attack, heart rhythm problems, blockages, or congestive heart failure.

People who are 65 years and older should not take this drug because the side effects can be more extreme. There are other medications that can be used to treat your condition that are safer and more effective if you are in this age group.

Patients with hepatic impairment (liver failure) are generally more susceptible to drugs with potentially sedating effects like cyclobenzaprine.

Tell your doctor if you are on any medication for depression, seizures, allergies, coughs, or colds, or if you take sedatives, sleeping pills, tranquilizers, or vitamins.

Before prescribing this medication, your healthcare provider should also know if you've ever been diagnosed with overactive thyroid, glaucoma, or if you've ever had difficulty urinating.

You should always tell your healthcare professional about all prescription, non-prescription, over-the-counter, illegal and recreational drugs, herbal remedies, nutritional and dietary supplements, and any other drugs and treatments.

Cyclobenzaprine “High” and Abuse

Numerous online and anecdotal reports suggest that some people abuse cyclobenzaprine for a narcotic-like "high" because it can cause drowsiness.

Cyclobenzaprine can induce moderate to severe anticholinergic effects — meaning, it may disrupt the activity of certain neurotransmitters in your brain — at higher doses. This can lead to physical and mental impairment.

At even higher doses, cyclobenzaprine may cause severe ataxia, a neurologic condition in which you lose control of your muscle movements.

According to the Los Angeles coroner's office, singer Whitney Houston had five drugs in her system when she drowned in her hotel bathtub in 2012, including cyclobenzaprine.

Take cyclobenzaprine only as directed by your doctor, and keep this and all other drugs away from children, teenagers, and anyone for whom the drug was not prescribed.

Pregnancy and Cyclobenzaprine

Discuss a current or planned pregnancy with your doctor before taking cyclobenzaprine.

This drug should only be taken during pregnancy if the benefits outweigh the risks. Your doctor can help you decide if it's right for you.

Also tell your physician if you're breastfeeding or plan to in the future. It's not known if cyclobenzaprine passes into breast milk, but studies show it has happened with similar drugs.

Cyclobenzaprine Side Effects

Common side effects of cyclobenzaprine include:


Serious side effects of cycolobenzaprine include:

  • Fast or irregular heartbeat
  • Mood or mental changes (like confusion or hallucinations)
  • Trouble urinating
  • Chest pain
  • Fever
  • Seizures


  • Rash
  • Itching
  • Swelling (especially in the face, tongue, or throat)
  • Severe dizziness
  • Trouble breathing


  • Confusion
  • Agitation or restlessness
  • Dilated pupils
  • Headache
  • Changes in blood pressure
  • Changes in body temperature
  • Nausea or vomiting
  • Severe diarrhea
  • Rapid heart rate
  • Loss of muscle coordination or twitching
  • Shivering or goosebumps
  • Heavy sweating

Cyclobenzaprine Interactions

Taking cyclobenzaprine with a MAOI can cause a life-threatening reaction.

In at least one clinical study, the risk of serotonin syndrome (excessive serotonin in the brain leading to a potentially fatal combination of symptoms) occurred in patients that mixed cyclobenzaprine with serotonergic drugs like duloxetine (Cymbalta).

Cyclobenzaprine can also interact with central nervous system (CNS) depressants like opioids, benzodiazepines, nonbenzodiazepines, phenothiazines, certain chemotherapies, and barbiturates.

Tricyclic antidepressants, like amitriptyline (Elavil) and imipramine (Tofranil), combined with cyclobenzaprine can also increase the chance of side effects.

Alcohol and Cyclobenzaprine

This medication can make you drowsy. Drinking alcohol could increase this effect.

For your safety, avoid drinking alcohol while taking cyclobenzaprine.

Cyclobenzaprine Dosage

Cyclobenzaprine is taken by mouth. It comes as a tablet and an extended-release capsule.

Your doctor is likely to start you on 5 milligrams of the regular release tablet, three times a day.

The extended-release tablet is dosed once a day. This dose could be increased if you aren't getting relief from pain.

This drug is not meant to be taken long-term. Studies show it decreases pain for the first two weeks, peaking in the first few days but has no proven benefit after that.

Don't take this drug for more than three weeks without talking to your physician.

Patients with liver problems or who are over 65 years old may start at lower doses.

Always take cyclobenzaprine with a full glass of water and always swallow the medication whole.

Cyclobenzaprine Overdose

Symptoms of cyclobenzaprine overdose include:

  • Chest pain
  • Convulsions
  • Hallucinations
  • Vomiting
  • Rapid heartbeat
  • Drowsiness
  • Slurred speech

If you suspect an overdose, seek emergency medical attention or call a poison-control help line at 1-800-222-1222.

Missed Dose of Cyclobenzaprine

Take the missed dose of cyclobenzaprine as soon as you remember.


Don't "double up" on this medication to make up for a missed dose.

Cyclobenzaprine Pictures

Cyclobenzaprine 10 mg-SCH, white, round, film coated
Cyclobenzaprine 10 mg-WAT, white, round, film coated
Flexeril 5 mg, peach, pentagonal, film coated
Cyclobenzaprine 5 mg-WAT, white, round, film coated
Cyclobenzaprine 10 mg-AMN, yellow, round,
Flexeril 10 mg, yellow, pentagonal,
Cyclobenzaprine 10 mg-MYL, orange, round, film coated
Cyclobenzaprine 10 mg-MUT, white, round, film coated
Cyclobenzaprine 10 mg-TEV, yellow, round, film coated
Cyclobenzaprine 5 mg-MYL, blue, round, film coated
Cyclobenzaprine 10 mg-GG, yellow, round,

Cyclobenzaprine FAQ

Q: I am unable to get a cyclobenzaprine 10 mg prescription filled for a week, and I am out of this medication. I can't seem to reach my doctor. Is there an equal over-the-counter medication to replace it?

A: Cyclobenzaprine (Flexeril) is a muscle relaxer which works by blocking nerve impulses (or pain sensations) that are sent to your brain. There are no muscle relaxers available over-the-counter in the United States. To help with skeletal pain until you get a prescription from your doctor, you may try patches such as Thera-Patch over the counter.