Botox is basically a balancing act between competing muscle groups, in addition to the usual relaxation of areas that are hyperdynamic or form too many wrinkles.
If you haven't already had this done, it is a nice solution for the drooping brow problem.
The most common cause for a drooping brow is Botox to the frontalis, or up and down oriented muscle of the forehead, causing it to relax and the brows to descend. So while the across the forehead wrinkles are reduced, the brow position must also be considered.
Once you have found a doctor you are comfortable with, you and he or she will be able to micromanage your very individual muscle groups.