A biased view of µ opioid receptors?

The field of biased agonism has grown substantially in recent years and the mu-opioid receptor has been one of the most intensively studied receptor targets for developing biased agonists. Yet, despite extensive research efforts, the development of analgesics with reduced adverse effects remains a significant challenge. In this review we discuss the evidence to support the prevailing hypothesis that a G protein-biased agonist at the mu-opioid receptor would be an effective analgesic without the accompanying adverse effects associated with conventional mu-opioid agonists. We also assess the current status of established and novel m-opioid-receptor ligands that are proposed to be biased ligands.