There are no pills or “injections” that you can safely use to increase your breast size. The size of a woman’s breasts can vary from person to person and they can also change throughout a woman’s lifetime. If you lose a significant amount of weight, your breasts may become smaller and if you gain weight, your breasts may become larger. A woman’s breasts may also become larger during pregnancy and while breast feeding, and sometimes girls who are on birth control pills notice a slight increase in breast size. Although some women have plastic surgery to increase their breast size, there are many risks that should be carefully considered before going that route.