Flexeril (Cyclobenzaprine HCl)

  • Generic name: Cyclobenzaprine hydrochloride
  • Brand names:
    Flexeril (tablets 5 mg, 10 mg)
    Fexmid (tablets 7.5 mg)
    Amrix (extended-release capsules 15 mg, 30 mg)
  • Drug class: Skeletal muscle relaxant

What is Cyclobenzaprine used for?

Cyclobenzaprine hydrochloride (Flexeril), along with physical therapy, is used to relieve pain, cramping, and tightness associated with strains, sprains, spasms or other muscle injuries. It relieves muscle spasms of local origin, but is not effective in spasms which originate from diseases in the brain or spinal cord.

Off-label uses include fibromyalgia (a condition that involves aches, stiffness, and fatigue), neck or back pain, and headaches.

Cyclobenzaprine is used short-term, usually for 2 to 3 weeks. It provides quick and lasting symptom relief.

Strict contraindications

  • Concomitant or recent (within 14 days) use of MAO inhibitor
  • Hyperthyroidism
  • Congestive heart failure, arrhythmias, heart block or conduction disturbances, acute recovery phase of MI

How long does it take for Cyclobenzaprine to work?

It takes from 30 minutes to 1 hour for muscle relaxation to be achieved.

How long does Cyclobenzaprine last?

The duration of action ranges from 12 to 24 hours. The half-life of cyclobenzaprine is about 18 hours, so it is eliminated quite slowly. It usually takes 4-5 days to leave the system.

Is Cyclobenzaprine addictive?

Cyclobenzaprine is not classified as a controlled substance in the United States, and is therefore considered non-addictive.

Further reading


  • 1. Flexeril PDR Physicians' desk reference. 52nd ed. Oradell, NJ: Medical Economics Company, 1998; p.1656-7.

Last updated: February, 2015

Advanced Consumer Info

flexeril 10mg

  • Pregnancy category: B
  • Breastfeeding: It is unknown if cyclobenzaprine is excreted into human milk.
  • Mechanism of action: Cyclobenzaprine relieves muscle spasms through a central action, at the level of the brain stem, with no direct effect on the neuromuscular junction or the muscles.
  • Elimination half-life:ranges from 1 to 3 days.
  • Advantages:
    Cyclobenzaprine is not habit forming.
  • Disadvantages:
    As cyclobenzaprine hcl is closely related to the tricyclic antidepressants it may have some toxicity in overdose and in combination with other drugs.