whats the best medicine to become my boobs smaller?

There is no medicine which will reduce the size of your breasts.  I suggest consulting with a Board Certified
Plastic Surgeon where you can be examined and advised of your surgical
options.  Together you can decide what
options are available to you in order for you to receive the results you are
looking to achieve.  Ask to view before
and after photos.

If there is a  problem with the breast size, there are no medications unfortunately to make difference in the size, in either direction.  If one is comfortable with the idea of surgery, there are very good surgical options.  If one is not comfortable with the idea of surgery, one will have to learn to make do with various bras and clothing options to make the breasts "seem" smaller or larger, as desired.

No, despite what you may hear/read about, there is no effective medication or lotion to help reduce breast size. If your breast size is a concern, seek consultation with board certified plastic surgeons.  Ask to see lots of examples of their work and communicate your goals clearly.Best wishes.