The dilemma of opioid-induced hyperalgesia and tolerance in chronic opioid therapy.

Opioids have been used for decades and continue to be used to treat severe, acute, chronic non-cancer and cancer pain.1,2 They work mainly by inhibiting spinal cord neuronal transduction and the ascending pain signals at midbrain nuclei, and through the modulation of limbic system pain perception.3 The main opioids receptors are mu and kappa receptors.1–3 The use of opioids can be challenging and not without severe or life-threatening side-effects.1,2 The World Health Organization (WHO) has recommended the adoption of a three-step analgesic ladder to meet the therapeutic challenges of administering opioids and to reduce the incidence of these side-effects. This can be achieved by starting with non-opioid analgesics followed by weak opioids with adjuvants, reserving strong opioids for cases of severe pain.2,3