An increase in estrogen/progesterone causes a subsequent increase in breast size.
If you are planning on taking birth control pills be advised that there are other side effects than simple breast growth.
If you smoke you shouldn't take the pill, if you have circulation problems or high blood pressure, you shouldn't take the pill. There are many contraindications and considerations involved with this.
Please see your OBGYN for more information and a complete exam before you take any type of hormonal supplement.