It appears to involve more primitive aspects of the brain, activating deep structures that may block pain at a spinal level — similar to how opioidanalgesics work.
Methods: Using three ladders pain analgesic WHO introduced, that is the first ladder giving NSAIDs. The second weak opioid 'analgesics, the third strong opioidanalgesics.
The use of opioidanalgesics has a long history in clinical Settings, although the functions of opioid receptors, especially their role in the brain, are not well understood yet.