Moreover, a report examining co-administration of the KOR agonist nalfurafine with the MOR agonist oxycodone noted the reduction of both self-administration as well as respiratory depression, further suggesting that mixed action MOR/KOR ligands (Townsend et al., 2017) may have a superior safety profile over either classical or biased ligands at a single subtype, similar to the action ascribed presently to MP1207 and MP1208. Here, OPRK1 is linked to respiratory depression.