Lots of groundwork, but if its seriously not working try out chill
Groundwork d patience is your best bet!! Fixing the aggressiveness is better then buying a temporary solution to the problem!
For a mare mare magic or smart calm pellets from smart pack
Groundwork is your friend. There's no product that be applied to fix an aggressive horse, and even if there was it would most likely be a tool to force the horse into submission rather than treating the root cause of the problem. If your horse is aggressive, building a solid foundation on the ground is SO important as it will create a trust between the two of you and will give you a much better insight into your horse. Horses are not naturally aggressive animals and they are usually aggressive for a reason. Make sure that your horse isn't in any pain, checking saddle fit, teeth, bit, shoeing/trimming ect... I've found through experience that aggressive horses often tent to be very intelligent horses and they need to be stimulated mentally as well as physically. Obstacles and quick moving tasks on the ground to keep them thinking are great things to do. But also never forcing them to do these things, aggressively horses do not react well to aggression and being forceful will only push the horses further into this state, so just remember to always be patient and know that the horse is never intentionally bad he only acts this way as a result of how he has been raised and taught in his past. (: