Usually the Lexapro takes awhile . I have taken Klonopin for 16 years - no side effects after the initial drowsieness, and NO panic since it got into my system and started working. If you could take the short acting benzo (Ativan), I think you would be perfectly safe taking the longer acting benzo (Klonopin). No use suffering waiting for the Lexapro to kick in ! Good luck with taking the Klonopin AS NEEDED tho - its not meant to work that way - it needs to build up in your system and stay at a constant level. I dont understand any Doc giving it as needed, but have read on the board some do. I would read up on it, or talk to your PDoc on WHY they gave it as needed. Good luck !