Opioids are a group of analgesic agents commonly used in clinical practice. The three classical opioid receptors are MOP, DOP and KOP. The NOP (N/OFQ) receptor is considered to be a non-opioid branch of the opioid receptor family. Opioid receptors are G-protein-coupled receptors which cause cellular hyperpolarisation when bound to opioid agonists. Opioids may be classified according to their mode of synthesis into alkaloids, semi-synthetic and synthetic compounds. Opioid use disorder (OUD) is an emerging issue and important lessons can be learnt from the United States where opioid epidemic was declared as a national emergency in 2017.
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