Is morphine safe for dying patients?

Opioids bind to specific opioid receptors in the central nervous system and in other tissues. There are at least four major classes of opioid receptors: μ, κ, δ and possibly σ. In addition, there are two subtypes of μ receptor: μ1 and μ2.These are all G-protein coupled receptors acting on GABAergic neurotransmission. The pharmacodynamic response to an opioid depends on which receptor it binds, its affinity for that receptor, and whether the opioid is an agonist or an antagonist. For example, the supraspinal analgesic properties of the opioid agonist morphine are mediated by activation of the μ1 receptor, respiratory depression and physical dependence (dependency) by the μ2 receptor, and sedation and spinal analgesia by the κ receptor.