OverviewDosageSide EffectsInteractionsHalf-Life

Generic Name: Cyclobenzaprine
Brand Names: Amrix, Fexmid, Flexeril
Drug Class: Muscle relaxant
Availability: Prescription needed
Molecular Formula: C20H21N
UNII: 69O5WQQ5TI

What is Cyclobenzaprine?

Cyclobenzaprine is a prescription-only muscle relaxant sometimes sold under the brand names Amrix, Flexeril, and Fexmid.

What is Cyclobenzaprine Used For?

Cyclobenzaprine is a muscle relaxant, or a medication that relaxes the muscles, designed for short-term use. Specifically, it works to relieve discomfort from muscle spasms. This drug is particularly popular because it is designed to work without interfering with muscular function.

How Does Cyclobeznaprine Work?

Experts aren’t currently 100% sure how cyclobenzaprine works. That being said, it is believed to work by acting upon the brain stem to affect certain neurons, thereby disrupting discomfort-signalling messages to the brain.

Importantly, this drug is a tricyclic antidepressant derivative and may result in potentially life-threatening serotonin syndrome when taken simultaneously with other drugs that increase serotonin levels, such as monoamine oxidase (MAO) inhibitors.

How Long Does it Take for Cyclobenzaprine to Work?

Most patients typically feel the effects of cyclobenzaprine within an hour of taking it, and the effects can last anywhere from 4 to 6 hours or longer depending on patient-specific factors.

Do Not Use Cyclobenzaprine If:

There may be some cases where the use of this drug is not recommended or its usage needs to be adjusted and/or closely monitored. These cases include:

  • Those who are allergic or otherwise hypersensitive to this drug of any of its components
  • People currently taking MAO inhibitors
  • People who stopped taking MOA inhibitors less than 14 days prior to planned cyclobenzaprine use
  • People with hyperthyroidism/overactive thyroid
  • Those with heart problems, including but not limited to arrhythmias, those recovering from a recent heart attack and heart block
  • People with liver issues
  • Patients with urinary retention
  • Patients who are on other medications that may interact with cyclobenzaprine
  • Patients of elderly age

Note that this list may not be complete.

Disclaimer: this article does not constitute or replace medical advice. If you have an emergency or a serious medical question, please contact a medical professional or call 911 immediately. To see our full medical disclaimer, visit our Terms of Use page.


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