Arnica is a plant (http://en.wikipedia.org/wiki/Arnica), which when taken in cream or tablet form, can help to reduce bruising and aid healing, especially of the muscles. However, it is an anti-coagulent too, which means it thins the blood. Unless your surgeon has specifically recommended taking Arnica, don’t take it. Especially not if you’re taking other blood thinners like aspirin, ibuprofen, or warfarin. It can cause the stitches to open up and delay healing, or if you’re pre-op it can predispose you to heamorrage. A lot of girls on here take it without understanding the risks. Ask your surgeon what he/ she recommends.
Once your scars are fully healed (around 6 weeks) you should be ok to use Arnica. It works a miracle on bruising. I have always used the cream, but you can buy cream or tablet form from boots or any chemist.