2.1  Understanding pain

Pain has traditionally been perceived as a subjective experience and is usually indicative of some underlying condition, injury or trauma. It is an experience that is crucial for survival since it induces the sufferer to avoid risk of injury and promote well-being. The experience of pain is the single most common reason why people attend surgeries or take self-medication. It is also, in its chronic form, the third greatest problem in human health after cardiovascular disease and cancer, causing a huge economic burden in absence from work, lost productivity and healthcare costs. Until fairly recently, the mechanisms by which pain was perceived were poorly understood. Its treatment was by means of empirically-derived medicines or by attempting to relieve the underlying cause of the pain with surgery. One visible clinical manifestation that often accompanies pain is inflammation and efforts to reduce this frequently result in a reduction of accompanying symptoms.

Historically, neither inflammation nor pain has been managed using rationally-designed drugs. The agents that were discovered empirically usually provided the starting point for greater understanding. Within the last 20 years an increasing understanding of the mechanisms by which pain itself is experienced has arisen, especially chronic neuropathic pain (that which is not accompanied by visible symptoms) and this has enabled usable models to be set up for testing hypotheses and developing new treatments. It is evident that the immune system plays a central role, eliciting reactions both in the peripheral and central nervous system as well as mediating the classical inflammatory response.