Another approach to the control of pain relates to the activity of naturally occuring morphine-like substances called endorphins. Endorphins are produced by the body as a means of controlling pain. Pain sensitive structures respond to endorphins when the endorphins attach to specific sites on their surface called receptors. Certain parts of the brain and spinal cord are rich in endorphins and their receptors. Any technique which increases their activity reduces pain. In the spinal cord they inhibit the forward transmission of pain impulses. In the brain they reduce the appreciation of pain.

 There is some evidence to suggest that the body increases its production of endorphins just prior to labour. In addition to counterstimulation TENS may also work by stimulating the release of endorphins within the spinal cord. Opioid drugs like morphine, pethidine and fentanyl look like endorphins and so are able to fit into their receptors. In this way they mimic their effects.

 The effects of endorphins are specific to pain transmitting nerves. Unlike local anaesthetics which can ‘block’ nerves carrying normal touch and movement control, opioid drugs given in epidurals only affect pain transmitting nerves.