I use Regumate (prescribed by vet) to stop a really stroppy mare from being really stroppy! It has made such a difference to her. She would come into season and would be 'winking' at any horse the second she came into contact (irrespective of whether they were mare or gelding). At shows, she would be vile, lose her manners and call to anything that moved. She had been a brood mare prior to my owning her (she's now 10).
She is much, much calmer and although I still get some of the behaviours, they are now considerably reduced and manageable. She is now more of a pleasure to own and my only anxiety is that I can't imagine taking her off the drug.
I also know of two other mares who are also on Regumate for the same reason.