At the most basic level, all back pain is caused by damage to the nervous system. The nerves simply produce pain in response to a harmful event (thereby alerting the brain to the problem). The pain is detected by special receptors in the body, and then transmitted, usually via the spinal cord, to the brain.

Different painkillers have their own, individual way of operating, but, in essence, they all prevent pain signals from reaching the brain. Aspirin and ibuprofen, for example, block the formation of chemicals (known as prostaglandins) that stimulate the pain receptors in the body and without this, the pain signal is not produced in the first place.

Local anaesthetics, such as Novocaine, provide pain relief by preventing the transmission of the pain signal, from the receptors to the brain the signal is produced, but it does not go anywhere.

Finally, morphine and other opiate drugs mimic the effects of naturally occurring brain chemicals (endorphins, for example) that alter our perception of pain, making it appear less noxious; in essence, the signal gets through to the brain, but it is interpreted differently.