OPRM1 and Respiratory insufficiency due to muscle weakness: During an overdose, there is a sustained effect on the brainstem and cortical centres regulating respiratory rate, resulting in respiratory depression and potentially death.146 Initial management should focus on protecting the airway and maintaining breathing and circulation as in any emergency situation.147, –149 Naloxone is a competitive mu-opioid receptor antagonist, which reverses central and peripheral opioid effects rapidly.