28289
OBJECTIVE : This study examined the effect of cocaine self - administration on behavioral indices of sleep and alternatively the effect of sleep disruption on cocaine - maintained responding by rhesus monkeys .
 Chemical: cocaine; Chemical: cocaine
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: cocaine; Chemical: cocaine