Good Afternoon,
It is worth noting that Wyeth Pharmaceuticals currently has a
patent for Effexor XR. While there is a
generic extended release version of venlafaxine available, it is not exactly the same as the brand name (Because of the patent). The headaches you are experiencing may be caused by some of the inert ingredients in the generic brand. Knowing this, I would take the samples back to your Dr. and continue using the brand name since you already know it works for you.