n. a drug used for the treatment of acute skeletal muscle spasm (see muscle relaxant). Structurally related to the tricyclic antidepressants, it has many features in common with them, including sedation and significant anticholinergic effects. Low doses are moderately effective in treating fibromyalgia. Because of its resemblance to the tricyclic drugs, cyclobenzaprine should not be taken concurrently with monoamine oxidase inhibitors. U.S. trade name: Flexeril.