22691
Several characteristics of these compounds suggest a classic " opioid " mechanism of action : nanomolar affinity for opioid receptors , competitive interaction with the opioid receptor antagonist naloxone , and two - way analgesic cross - tolerance with morphine .
 Chemical: naloxone; Chemical: morphine
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: naloxone; Chemical: morphine