They are almost the same drug. Pristiq is Effexor with some of it cut out. That supposedly makes it have fewer side effects and be a little easier to stop taking, but that usually doesn't turn out to be all that true. The same was done with Celexa to create Lexapro. That makes the change pretty easy. But they can feel quite different in how they effect you, even though they are quite similar, so be on the alert for that.