Cyclobenzaprine hcl is a long-acting skeletal muscle relaxant which relieves muscle spasms and improves signs and symptoms such as pain, tenderness, limitation of motion, and restriction in activities of daily living. It is closely related to the first-generation tricyclic antidepressants.

The principal side effects of cyclobenzaprine are drowsiness, dry mouth or tongue, dizziness and bad taste.


Cyclobenzaprine after its synthesis in 1961 was found to have limited antidepressant action with no significant advantage over other tricyclics. However it was found to act as a centrally acting muscle relaxant and has been widely used ever since.

Cyclobenzaprine was approved by the U.S. Food and Drug Administration in 1977 for the treatment of acute muscle spasms of local origin. Cyclobenzaprine is sold as a hydrochloride salt in a 10 mg non-scored tablet under the trade name Flexeril (Merck and Co.) or as a generic (Genera, Warner-Chilcott, Duramed, Mylan, Endogenerics, and Watson).

Once-a-day extended release formulation, Amrix, has been approved by the FDA in 2007 and is available in 15 and 30 mg capsules.

FDA approved uses
  • Adjunct to rest and physical therapy for relief of muscle spasm associated with acute, painful musculoskeletal conditions

A muscle spasm is an uncontrollable contraction of a muscle. Cyclobenzaprine only works to relieve muscle spasms caused by problems in the muscles. It is ineffective in muscle spasm due to central nervous system disease.

Off-label & Investigational uses
  • Fibromyalgia1, 3
    Cyclobenzaprine may be helpful for sleep and pain control in fibromyalgia.
    The usual starting dose is 5-10 mg taken at bedtime. The dose may be increased to 20-30 mg, taken either at night or in divided doses during the day. Compared with amitriptyline, cyclobenzaprine is associated with better patient acceptance due to fewer side effects and more rapid onset of relief.
    Cyclobenzaprine has been studied in the treatment of fibromyalgia. In a study of 120 fibromyalgia patients, those receiving Cyclobenzaprine (10 to 40 mg) over a 12 week period had significantly improved quality of sleep and pain score. Interestingly, there was also a reduction in the total number of tender points and muscle tightness.
    A meta-analysis of cyclobenzaprine showed that it was superior to placebo for treating fibromyalgia but that it was not as effective as antidepressants.
  • Tension headaches2
    In a 1972 double-blind study, 10 of 20 patients receiving cyclobenzaprine experienced a 50% or greater improvement in tension-type headache, compared with only 5 of 20 patients receiving placebo. The usual dose of cyclobenzaprine is 10 mg at bedtime.
  • Insomnia
  • Migraine
  • Levator ani syndrome
  • Tinnitus 4
    Cyclobenzaprine may attenuate some forms of tinnitus, e.g. noise-induced tinnitus.

Cyclobenzaprine "pros" and "cons"


  • Effective. Quick and lasting symptoms relief (back pain, neck pain, muscle spasms)
  • The best-studied muscle relaxant in the treatment of musculoskeletal conditions
  • No potential for abuse and dependence.
  • May be useful in patients with insomnia because of severe muscle spasms.
  • Pregnancy category B. Cyclobenzaprine is considered to be safe during pregnancy.

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