A nerve block is the injection of medication onto or near the nerves. It involves the use of a tiny needle attached to a syringe containing medication to decrease or stop passage of nerve impulses that may carry pain signals to the brain or spinal cord. Nerve blocks are an alternative treatment to drugs or other ineffective treatments used to control pain. Nerve blocks are effective for many headache conditions, including migraine and cluster headache. The medications injected include a local anesthetic and sometimes a steroid.