BPR is a semi-synthetic derivative of thebaine, one of the most chemically reactive morphine alkaloids. Compared with morphine, the usefulness of BPR is 20–40 times higher than that of morphine because morphine is a full μ-opioid agonist but BPR is a partial μ-opioid agonist that indicates high affinity and slowdissociation from the μ-opioid receptor.