sentences:  Nalmefene acts as an inverse agonist of the μ-opioid receptor (MOR) (Ki = 0.24 nM) and as a weak partial agonist (Ki = 0.083 nM; Emax = 20–30%) of the κ-opioid receptor (KOR), with similar affinity for these two receptors but a several-fold preference for the KOR.