Abstract: Opioids can activate the pro-nociceptive channel by which the sensitivity to pain has been increased, which is called opioids induced hyperalgesia (OIH). The mechanism of OIH has not been identified, but it is possibly involved in the increased activity of central glutamatergic system, changed function of opioid receptors, roles of peripheral receptors, effects of endogenous neuropeptides, decreased function of inhibitory neurotransmission system, and changed elements in signal transduction pathway, etc.

Key words: opioids, hyperalgesia, molecular biology, review