Britty is right - the LAST thing a woman wants to do is pump herself full of hormones... the chances of getting breasts cancer are a lot better than any temporary breast growth and the benefits are massively outweighed by any potential gains.
That said - I had a friend who went on birth control and swelled substantially... but that's a lottery... for a lot of girls, it might do nothing and even if one works for a girl, another might not... not exactly reliable... but I suppose it stops you getting children accidentally.
I forgot to post this before... but as this thread is active again, I shall post it... It may be nothing you hadn't heard before but have a look.
Macrolane not exactly going to make a girl burst out of her top but still.