Cyclobenzaprine: Action Mechanism, Warnings, Abuse, Side Effects, Interactions and Dosing

This medication is often part of a general recovery plan that includes rest and physical therapy.

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

It is also available under the Fexmid and FusePaq brands.

Cyclobenzaprine is also prescribed off-label to treat fibromyalgia .

Mechanism of action

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

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


Do not take cyclobenzaprine if you have 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).
  • Rasagilina (Azilect).
  • Selegilina (Emsam).
  • Tranylcypromine (Parnate).

The combination of an MAOI with cyclobenzaprine can cause very serious and life-threatening side effects.

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

People over 65 should not take this medicine because the side effects may 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 are generally more susceptible to drugs with potentially sedating effects such as cyclobenzaprine.

Tell your doctor if you are taking 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 have ever been diagnosed with an overactive thyroid , glaucoma, or if you have ever had difficulty urinating.

You should always inform your health professional about all prescription, non-prescription, illegal and recreational medicines, herbal remedies, dietary and nutritional supplements, and any other drugs and treatments.

“High” cyclobenzaprine and abuse

Numerous online and anecdotal reports suggest that some people abuse cyclobenzaprine for a “high” narcotic effect because it can cause drowsiness.

Cyclobenzaprine can induce moderate to severe anticholinergic effects, that is, it can alter the activity of certain neurotransmitters in the brain at higher doses. This can lead to physical and mental deterioration.

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

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

Take cyclobenzaprine only as directed by your doctor, and keep this and all other medications away from children, adolescents and anyone for whom the medication has not been prescribed.


Discuss a current or planned pregnancy with your doctor before taking cyclobenzaprine. This medicine should only be taken during pregnancy if the benefits outweigh the risks. Your doctor can help you decide if it is right for you.

Also tell your doctor if you are breast-feeding or plan to do so in the future. It is not known if cyclobenzaprine passes into breast milk, but studies show that it has happened with similar medications.

Side effects of cyclobenzaprine

Common side effects of cyclobenzaprine include:

  • Drowsiness.
  • Dizziness.
  • Dry mouth.
  • Constipation .
  • Fatigue.

Tell your doctor if any of these side effects persist or worsen.

Serious side effects of cyclobenzaprine include:

  • Rapid or irregular heartbeat.
  • Mood or mental changes (such as confusion or hallucinations)
  • Problems urinating.
  • Chest pain.
  • Fever.
  • Convulsions

A very serious allergic reaction is rare, but seek immediate medical attention if you develop any of the following:

  • Eruption.
  • Itch.
  • Swelling (especially on the face, tongue or throat)
  • Severe dizziness
  • Difficulty breathing.

The combination of this medication with some antidepressant medications could cause serotonin syndrome and can be fatal. Symptoms of serotonin syndrome include:

  • 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 spasms.
  • Trembling or chills.
  • Heavy sweating


Taking cyclobenzaprine with an 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 who mixed cyclobenzaprine with serotonergic drugs such as duloxetine (Cymbalta).

Cyclobenzaprine may also interact with central nervous system (CNS) depressants such as opioids, benzodiazepines, non-benzodiazepines, phenothiazines, certain chemotherapies, and barbiturates.

Tricyclic antidepressants, such as amitriptyline (Elavil) and imipramine (Tofranil), combined with cyclobenzaprine may also increase the possibility of side effects.

Alcohol and cyclobenzaprine:

This medicine may cause drowsiness. Drinking alcohol may increase this effect. For your safety, avoid drinking alcohol while taking cyclobenzaprine.


Cyclobenzaprine is taken orally. It is presented as a tablet and a prolonged-release capsule. Your doctor may prescribe 5 milligrams of the regular-release tablet three times a day. The extended-release tablet is dosed once a day. This dose may increase if you are not receiving pain relief.

This medicine should not be taken long term. Studies show that pain decreases during the first two weeks, peaking in the first few days, but has no proven benefit after that.

Do not take this medication for more than three weeks without consulting your doctor. Patients with liver problems or those older than 65 may start with lower doses. Always take cyclobenzaprine with a full glass of water and always swallow all the medication.

Cyclobenzaprine overdose

Symptoms of cyclobenzaprine overdose include:

  • Chest pain.
  • Convulsions
  • Hallucinations
  • He retched.
  • Fast beats
  • Drowsiness.