What is Flexeril? Flexeril (cyclobenzaprine) is a muscle relaxant. Flexeril works by blocking nerve impulses (pain sensations) sent to your brain. Flexeril is a medicine commonly used for muscle spasms from musculoskeletal conditions of sudden onset. Order Flexeril online overnight to relax your muscles after strenuous exercise. Flexeril is not helpful in cerebral palsy. OneRead More