As to your question about
Pristiq, well, this is a pharmaceutical issue.
Pristiq is to Effexor as Lexapro is to Celexa, meaning it's quite similar to Effexor but missing some of the elements so a new patent could be had. Theoretically, Lexapro was thought to be easier to tolerate than Celexa when the same thing was done with those two meds, but whether that's true or not is unclear.