3997
Thus , caffeine ( 3 . 3 mg / kg ) versus placebo was tested in 48 healthy men ( aged 20 to 35 years ) selected after screening on 2 separate occasions .
 Chemical: caffeine
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Disease, Chemical 
Text: {0} 
Answer:
 Chemical: caffeine