The best over-the-counter medicine for back pain is Oxycodone, which is a narcotic that is an opioid agonist. It works by mimicking the actions of endorphins and enkephalins, which are naturally produced by the body in response to injury or disease. The drug acts on the brain's opioid receptors, which are located in the spinal cord and brain stem.

Oxycodone belongs to a class of drugs known as opiates. Opioids work by binding to specific receptors found on cells throughout the body (including those in the brain). When these receptors are activated, they cause changes in the way that cells function. These changes include dilation of blood vessels, reduction in blood pressure, stimulation of certain glands and inhibition of nerves that control pain sensation.