Injection therapy involves using a needle and syringe to inject anesthetic, corticosteroid, opioid or other medication into a person's body to relieve pain that does not respond to other forms of treatment. It is usually more effective in treating acute pain but may also be used to treat chronic pain.

During these treatments, medication is injected into the soft tissues, joints and other areas in and around the source of a patient's pain. Exactly how these injections exert their analgesics effects remains unclear.

The pain-relieving properties of injection therapy function in different ways depending on the site of the injection. In some cases, the injection is made into the epidural space, the area between the spinal sac and inside of the spinal canal (but not in the spinal fluid). The injected medication moves up and down the spine and coats the nerve roots and the outside lining of the spine’s facet joints (adjacent vertebrae) near the injection area. In other cases, the injection may be made directly into the facet joint, which may decrease inflammation in the joint.

Depending on the source of a patient's pain, injections also may be made into various joints. For example, injection therapy into the joint that connects the bottom of the spine with the hip (sacroiliac joint) may help to relieve back pain. Injection therapy also may be used to help relieve pain associated with arthritis, particularly in a patient's knees. Medications such as hyaluronate may act as a lubricant to the joint, which usually decreases pain. In other cases, the injection is made into trigger points (areas that are tender to pressure).

A combination of anesthetic (to relieve pain) and corticosteroid (to reduce inflammation) is used in most injection therapy treatments. In some cases, an opioid (narcotic) medication also may be used to enhance pain relief.

Controversy remains over the effectiveness of some forms of injection therapy. For example, studies have not shown injection therapy to be effective in treating many types of back or neck pain. The most recent literature indicates that many forms of blocks including epidural steroid injections have not been found to have any long- term benefits.

In addition, certain patients are not good candidates for injection therapy. This includes people prone to excessive bleeding and those taking anticoagulants (medications that decrease the clotting ability of blood). In addition, some forms of injection therapy, specifically the use of corticosteroids, are not recommended for patients whose pain results from infection or some forms of cancer. Corticosteroids can reduce immune system response, so patients who are fighting any type of serious infection should not undergo treatment with this type of medication. In addition, spinal injections increase the risk of spreading the infection into the spine, which can lead to meningitis.