A muscle relaxant is a type of drug that causes muscle contraction to cease. Muscle relaxants act on the brain to cause an overall sedative effect on the body rather than acting directly on the muscle.
The drug works by blocking the effect of a chemical neurotransmitter at the neuromuscular junction. Muscle relaxants are typically prescribed early in a course of back pain, on a short-term basis, to relieve low back pain associated with muscle spasms.