Baclofen is a muscle relaxant used for treating spasm of skeletal muscles, muscle clonus, rigidity, and pain caused by multiple sclerosis. It is also injected into the spinal cord to treat severe spasticity, spinal cord injuries, and other spinal cord diseases.A generic version is available.aclofen is a muscle relaxant used for treating spasm of skeletal muscles, muscle clonus, rigidity, and pain caused by multiple sclerosis. It is also injected into the spinal cord to treat severe spasticity, spinal cord injuries, and other spinal cord diseases.