sentences:  It is thought that the KOR activation of nalmefene might produce dysphoria and anxiety.In addition to MOR and KOR binding, nalmefene also possesses some, albeit far lower affinity for the δ-opioid receptor (DOR) (Ki = 16 nM), where it behaves as an antagonist.Nalmefene is structurally related to naltrexone and differs from it by substitution of the ketone group at the 6-position of naltrexone with a methylene group (CH2).