Muscle Relaxers

Cyclobenzaprine HCL (Flexeril)

  • Generic name: Cyclobenzaprine hydrochloride
  • Brand names: Flexeril, Fexmid, Amrix
  • Dosages: 5 mg, 10 mg tablets
  • Pharmacologic category: Skeletal muscle relaxant
  • FDA approved: August 26, 1977
  • Habit forming? Possibly
  • Pregnancy risk factor: B
Medical uses

Cyclobenzaprine is a centrally acting muscle relaxant, intended for short-term use in the treatment of pain, tenderness, and limitation of motion caused by muscle spasms.

The most common side effects are drowsiness, dry mouth, fatigue and headache.

Cyclobenzaprine for Fibromyalgia

Cyclobenzaprine 10 mg (Flexeril) may be prescribed to treat the pain, stiffness, and sleep problems that occur with fibromyalgia. This is currently an unlabeled use of the drug.

For use in treating fibromyalgia, the usual starting dosage is 5 to 10 mg at bedtime.

How well Cyclobenzaprine works
People with fibromyalgia who take cyclobenzaprine seem to notice an overall improvement in their symptoms, and they especially note improved sleep1. The medicine's effects may decrease over time2.

Experts do not know exactly how this drug works to improve fibromyalgia. Cyclobenzaprine is chemically similar to amitriptyline, a tricyclic antidepressant, so researchers believe that the two drugs may work in similar ways.

Pharmacological characteristics
  • Elimination half-life: eliminated quite slowly, with an effective half-life of 18 hours (range 8-37 hours.
  • Metabolism: Hepatic via CYP3A4, 1A2, and 2D6; may undergo enterohepatic recirculation.
  • Excretion: Excreted primarily via kidneys.
  • Quick and lasting relief of back pain, neck pain and muscle spasms
  • If taken at bedtime may help with insomnia due to the pain and spasms
  • Poorly tolerated: sedation and other CNS side effects are very common
  • Morning "hangover"
  • Range of toxicity is similar to tricyclic antidepressant overdose. Anticholinergic symptoms predominate, extreme cases may manifest with cardiac dysrhytmias and seizures.
Unlabeled uses
  • Fibromyalgia. Cyclobenzaprine have been used with some success to treat some fibromyalgia patients. It is administered to fibromyalgia patients typically in a dosage range of 5 to 30 mg per day.
    Data generally support its use in treating sleep and pain, and there are some data suggesting synergism when cyclobenzaprine is used with fluoxetine.
  • Tension headache3
  • Insomnia
Mechanism of action

Cyclobenzaprine is a centrally-acting skeletal muscle relaxant pharmacologically related to tricyclic antidepressants. It relieves skeletal muscle spasms of local origin without interfering with muscle function by acting within CNS at brain stem (reduces tonic somatic motor activity influencing both alpha and gamma motor neurons).

Reviews, Discussions Boards & Forums
  • 1. Tofferi JK, et al. (2004). Treatment of fibromyalgia with cyclobenzaprine: A meta-analysis. Arthritis and Rheumatism, 2004 Feb 15;51(1):9-13. PubMed
  • 2. Moldofsky H. Management of unrefreshing sleep in fibromyalgia. Rheum Dis Clin North Am. 2002 May;28(2):353-65. PubMed
  • 3. Lance JW, Anthony M. Cyclobenzaprine in chronic tension headache. Med J Aust 1972; 2:14091411

Last updated: February 10, 2015

Interesting facts


  • Cyclobenzaprine is structurally and pharmacologically related to tricyclic antidepressants.
  • Cyclobenzaprine does not fall within most governmental guidelines as a controlled substance.

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