Yes that is what the studies have shown.

Pristiq will not show improvement of effect with increasing the dosage like Effexor does.

Pristq is Effexor - supercharged - a chemical alteration of Effexor. However , the studies have shown that increasing dosages of Effexor will show increasing effects for the patient , while increasing the dose of Pristiq will not.

You can find more info in this Pristiq link. < This guy is constantly updating his information, and his resources, so you can always recheck the info.

Sorry for the late edit: If Pristiq is working for you, Great, Im not saying it isn't a good drug; as the link shows. And further studies may eventually gather enough to finally give it the ok on increasing dosage vs. effect, we can hope, for those on it.