I am in the process of switching from Effexor to Pristiq. Is there anyway of knowing whether the side effects (headache base of skull) is related to stopping the Effexor or starting the Pristiq.?? (started out as migraine) Was on Effexor 150mg and Dr ordered Pristiq 50mg. Felt worse on one Pristiq so I either take 2 tabs/day and alternate with one tab Pristiq and one Effexor the next day to control withdrawal. Have done this for 2 wks. Thanks...Carol G