My pdoc told me SSRI antidepressants (such as Lexapro) can cause rapid cycling. I've experienced that before. I know it is difficult to tell situational reactions vs. rapid cycling sometimes though. In my case, when I was on different SSRIs, my rapid cycling could not be mistaken as situational.....it was out of control. I learned the hard way I cannot take SSRIs. I agree this is a good question to your pdoc to help figure it out though.