403
No significant treatment effects were found , although there were trends towards a reduction in feeling tense and nervous by both drugs compared with placebo during the 7 . 5 % CO ( 2 ) challenge , and a reduction in alertness generally in the venlafaxine group compared with the pregabalin group .
 CO ( 2 ), venlafaxine, pregabalin
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 CO ( 2 ), venlafaxine, pregabalin