Hi Doctor, I have been taking 300 mg. Wellbutrin XL and 150 mg. Effexor XR for several years. I have recently increased Effexor by another 37.5 mg. but constipation has become almost unmanageable. Would it help to switch the Effexor to Pristiq and if so, what dose of Pristiq would be comparable to 150+ mg. Effexor? Also, can I expect a further decrease in libido from Pristiq? Thank you. Katie