6780
Prechronic treatment with all drugs except naltrexone ( 1 - 10 mg / kg ) produced dose - related decreases in responses rates .
 Chemical: naltrexone
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: naltrexone