24498
Twenty healthy volunteers received single doses of methylphenidate ( 40 mg ) and placebo on separate test days according to a double - blind , cross - over study design .
 Chemical: methylphenidate
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: methylphenidate