SAG and Respiratory insufficiency due to muscle weakness: While the current dogma is that, for μ receptor agonists, respiratory depression results from activation of arrestin signalling (see Chan et al., 2017; Madariaga‐Mazón et al.,2017; Roth et al.,2017; Smith et al.,2018), there is evidence that signalling through Gi/Go is also involved in mediating this behaviour.