19919
The global DNA methylation status in the brain and liver of mice chronically treated with cocaine or heroin remains unaffected , but this finding cannot exclude the existence of anatomical region or gene - specific methylation differences .
 Chemical: cocaine; Chemical: heroin
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: heroin