Flexeril is the brand name of a drug used as a muscle relaxant. It's prescribed most often for the relief of muscle spasm and pain.
There are many types of muscle relaxants on the market. A review of studies shows different types of muscle relaxants are equally effective for acute low back pain.
According to the drug manufacturer, Flexeril is not a substitute for the physical therapy, rest, or exercise. Flexeril relieves the pain of strains and sprains, but it's not useful for other types of pain.
It should be used only for short periods (no more than three weeks). There's generally no reason to use it for a longer period since the type of injury that Flexeril treats should get better in a few weeks.