Cyclobenzaprine is a centrally-acting muscle relaxant which boosts levels of norepinephrine and binds to serotonin receptors in the brain to reduce spasm. Cytochromes P-450 3A4, 1A2, and, to a lesser extent, 2D6, mediate N-demethylation, one of the oxidative pathways for cyclobenzaprine. Cyclobenzaprine relieves skeletal muscle spasm of local origin without interfering with muscle function. Drowsiness, fatigue and sedation (up to 40%) is the most common side effect of Cyclobenzaprine. It may have life-threatening interactions with monoamine oxidase (MAO) inhibitors. Postmarketing cases of serotonin syndrome have been reported during combined use of cyclobenzaprine and other drugs such as selective serotonin reuptake inhibitors (SSRIs), serotonin norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants (TCAs), tramadol, bupropion, meperidine, verapamil, or MAO inhibitors.

Norcyclobenzaprine (aka desmethylcyclobenzaprine) is one of the major metabolites of cyclobenzaprine which is a muscle relaxant marketed under the brand name Flexeril. Both cyclobenzaprine and norcyclobenzaprine are known to be potent antagonists of the serotonin 2a receptor.