opioid agonists and agonist/antagonists comprise a heterogeneous body of compounds that can be partitioned into at least three groups on the basis of their discriminative stimulus properties in several animal species : ( 1 ) stimulus effects similar to those of morphine or fentanyl and blocked completely by low doses of antagonists , such as naloxone and naltrexone ;
C0027358
naloxone
C0027360
naltrexone