An epidural is a potent steroid injection that helps decrease the inflammation of compressed spinal nerves to relieve pain in the back, neck, arms or legs. Cortisone is injected directly into the spinal canal for pain relief from conditions such as herniated disks, spinal stenosis, or radiculopathy. Some patients may need only one injection, but it usually takes two or three injections, given two weeks apart, to provide significant pain relief.