CYCLOBENZAPRINE  treats muscle spasms. It works by relaxing your muscles, which reduces muscle stiffness. It belongs to a group of medications called muscle relaxants.   Research indicates that it primarily acts within the central nervous system in the brain stem. Cyclobenzaprine does not work directly on skeletal muscle or the neuromuscular junction, although an overlapping action on the spinal cord may contribute to its overall skeletal muscle relaxant activity