4000
Participants were then tested on 2 occasions after 12 - hour abstinence from caffeine in each of 2 protocols ; this required a total of 4 laboratory visits .
 Chemical: caffeine
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Disease, Chemical 
Text: {0} 
 Entities: caffeine 
Answer:
 Chemical: caffeine