How long will it take for birth control to clear up acne?

I have mild acne on mainly just my forehead. Will birth control clear that up quickly?How long will it take for birth control to clear up acne?
not at all. I'm on my third pack, and I never had that bad of acne before. Only an occasional 1 pimple a week or even a month.. Then BAM! I have at least five pimples every morning, not even regular pimples.. but painful cystic pimples. So, in a way it is gradually fading...i have to stick it till the end of july, and if it continues to give me acne, i will have to switch. But doctors said that they have to get worse before they get better. It may take you a week , even up to 6 months. And it depends on the birth control pill. I take lessina, yaz and yasmin treats acne well from what I heard.. My cheap *** doctor prescribed me lessina.