An epidural steroid injection for back pain is a common treatment to try to relieve the inflammation and irritation of the nerve root in the spine. The medication that is injected is a corticosteroid that is used in medicine to help relieve inflammation. By injecting it directly into the right area of the spine, the medication can work directly on the problem.
Usually, there is a type of local anesthetic also in the injection, along with the steroid.
Steroids can be dangerous if given for the wrong reason or taken incorrectly. However, this type of steroid does not go through your system (from swallowing it, for example) so is generally not a dangerous procedure. Of course, you should always discuss all the risks involved in a procedure like this before giving your consent.