How Birth Control Can Impact Your Breast Size

Some forms of birth control will change your breast size, and others won't.

Medications often have side effects, and the birth control pill is no exception.

There are two general categories of birth control pills: combination pills and progestin-only pills. Combination pills contain the hormones estrogen and progesterone, which combine to prevent ovulation (a.k.a. the process of your ovaries releasing an egg). Progestin-only pills don’t contain any estrogen, and they don’t prevent ovulation. Instead, they slow down the process of ovulation by thickening cervical mucus, which prevents sperm from reaching an egg, and thinning the lining of your uterus, which prevents a fertilized egg from attaching.

With both pills, the hormones you’re ingesting can cause a wide range of side effects, including bloating, mood swings, nausea, spotting and more.

If you’re a new user of the birth control pill and you’ve recently noticed that your bras don’t fit anymore, it’s possible that these two things are linked. We spoke with Canadian experts to find out why.

(Related: Does Melatonin Affect Birth Control? What Experts Want You to Know

Why birth control can change breasts size

Changes in breast size, specifically an increase in breast size, is a known side effect of combined birth control pills, explains Dr. Marjorie Dixon, CEO and medical director at Anova Fertility and Reproductive Health in Toronto.

“The hormones in a combined birth control pill, estrogen and progestin, act on the body in several ways,” she says. Namely, both hormones can effect the fat distribution in your body, especially in the hips and chest. “Estrogen also increases water retention, which can cause swelling throughout the body from the increased fluid,” Dixon says. “Both effects can contribute to increased breast size.”

Dr. Constance Nasello, an ob-gyn in Chatham, Ontario, also points to estrogen as the culprit for breast swelling and breast tenderness, which may lead to an increase in breast size. Although buying new bras may be inconvenient, both doctors say a change in breast size is nothing to be worried about from a health standpoint.

(Related: 9 Comfortable Wireless Bras Available in Canada

What to do if you don’t want your breasts to change size

The good news: there are other forms of birth control that won’t change your breast size.

“This effect is usually only seen when taking a combination pill,” Dixon says. “Long-acting reversible contraception (LARC) methods like the IUD [intrauterine device] or implant are great options for those who would like to avoid this effect on breast size.”

Next: What’s the Best Way to Switch Birth Control Pills?