According to an article in the journal Clinical Therapeutics, the duration of action of cyclobenzaprine hydrochloride is four to six hours. The medication relaxes muscles and is used in treating muscle spasms and extending the range of motion for patients with acute musculoskeletal conditions.
The Clinical Therapeutics article states that cyclobenzaprine is also effective at minimizing local tenderness and pain in the affected area. The typical dosage of the medication can result in sedation, which is the most frequently observed adverse side effect of the drug.
Drugs.com states that patients with thyroid disorders, congestive heart failure or heart rhythm disorders are among those for whom cyclobenzaprine is contraindicated. Anyone who has recently taken a monoamine oxidase inhibitor is also advised to avoid the drug.