Cyclobenzaprine

Cyclobenzaprine, sold under several brand names including, historically, Flexeril, is a muscle relaxer used for muscle spasms from musculoskeletal conditions of sudden onset. It is not useful in cerebral palsy. It is taken by mouth. Common side effects include headache, tiredness, dizziness, and dry mouth. Serious side effects may include an irregular heartbeat. There is no evidence of harm in pregnancy, but it has not been well studied in this population. It should not be used together with MAOIs. How it works is unclear. In any case, it is known to inhibit serotonin and norepinephrine reuptake and to block serotonin, adrenergic, histamine, and muscarinic acetylcholine receptors. Chemically, it is very similar to tricyclic antidepressants like amitriptyline. Cyclobenzaprine was approved for medical use in the United States in 1977. It is available by prescription as a generic medication. In 2023, it was the 47th most commonly prescribed medication in the United States, with more than 13 million prescriptions. It was not available in the United Kingdom as of 2012.