1 Mild analgesics pose particular problems in evaluation because of difficulty in getting suitable patients, the frequent use of oral administration and their long-term use. 2 Despite their limitations it is possible to quantify both pain severity and pain relief using either 'pain scores' or 'visual analogues'. 3 A trained observer can add information in addition to the patient's interpretatio...

The discovery of the opioid receptors began in the 1970s and three (μ, δ and κ) are now recognised. Most current opioid analgesics interact preferentially with μ receptors, although some have actions at δ and κ receptors. The revelation that opioid receptors are present on peripheral sensory neurones and immune system cells, has led to the realisation that the opioid system is involved in a hos...