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Study treatments were dosed incrementally over a three week period , to reach daily doses of 150 mg venlafaxine and 200mg pregabalin by the CO ( 2 ) challenge test day .
 venlafaxine, pregabalin, CO ( 2 )
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 venlafaxine, pregabalin, CO ( 2 )