I have taken Xanax, Klonopin and Ativan, and of the three, Klonopin is the slowest the act, but lasts the longets as far as calming effect. Ativan is middle-of the road; takes about 45 min to kick in, then its lights out. Xanax had a very quick reaction time for me (10-15 min) but its effects wore off after 3-4 hours.

I battle with panic attacks, so I have been on a lot of different dosages of all three meds, but Ativan is the newest one. I have to say, even tho it may take its time, Klonopin does the trick if the attack isn't too severe.

Jenn