Can botox in corrugator and procerus alone cause brow to drop?

Typically an injection in the corrugator muscles will not cause the brow to drop. If Botox migrated to muscles that were not intended for Botox, you may experience a drop. Some patients report a heavy feeling in their brow for the first week or so after a Botox injection. This however is a feeling and not esthetically visible. All the Best. 

The corrugator and procerus muscles are brow depressors, meaning when they are active they pull the medial brow downward.  Treating these muscles with Botox will relax them and cause the medial brow to "lift".  Inadvertent treatment of the frontalis muscle instead of these muscles would cause the brows to droop.  

The corrugator muscle is a depressor of the brows.  Meaning that when it is contracted the brow will drop.  The frontalis is an elevator of the brow.  When contracted it raises the brow.  So Botox to the corrugator alone will not cause brow droop.  The brow will only droop if the botox is injected into the wrong muscle.

Botox injected into the middle brow can cause the brow to droop if some of the frontalis was effected.  In some people the frontalis is lower than you think and often can be mildly effected with only corrugator and procerus injection.  Especially if the lateral portion of the corrugator was injected and the botox diffuses up into the frontalis.  Nothing you can do now but wait 2-3 months for the botox to begin wearing off.  Best of luck, Dr. Emer.

In my experience with Botox, I would say treatment of the horizontal lines across the forehead is what normally can cause some brow drop.  This does not happen all of the time and it is temporary.  The closer the injection is to the brow, the more likely that there will be some dropping of the brow.  I do not believe there is any significant brow drop with only treatment of the corrugators and procerus, but this is dependent on the placement of injections.