Large study: Certain birth control significantly increases breast cancer risk

Newly released results of a large-scale study reveal that certain progestin-only hormonal contraception can significantly increase the risk of developing breast cancer.

Key Takeaways:

• The study followed more than 2 million women from 2006 to 2019.

• It found an increased risk of breast cancer for women who took progestin-only hormonal birth control, specifically those containing Desogestrel, a synthetic progesterone.

• This is the second large study published this year that points to risks of hormonal birth control.

• Research shows that teen girls and women are not always made aware of the risks.

The Details:

The large study, published in Jama Oncology, followed more than 2 million women in Sweden from 2006 to 2019. Researchers investigated any potential association between different types of hormonal birth control and an increased risk of developing breast cancer.

The important findings revealed that certain hormonal contraceptives, especially those only containing desogestrel, a synthetic form of progesterone, can significantly increase the risk of breast cancer. Progestin-only products are more widely used in Sweden compared to other countries.

Desogestrel, often referred to as the "minipill,"works by thinning the uterine lining and thickening cervical mucus, in an attempt to prevent fertilization and implantation. It is often prescribed for those who cannot have birth control containing estradiol (synthetic estrogen) and is seen as a safe option. However, this study showed that it has serious risks associated with it.

The results of the study showed that “Oral formulations containing desogestrel were associated with a higher number of additional cases per 100 000 person-years compared to those containing levonorgestrel.” The researchers found that there is an increased risk even after less than one year of use.

“The finding that desogestrel may increase breast cancer risk more than other progestins is a novel finding that, to our knowledge, has not been previously reported," the researchers stated.

Most studies about hormonal birth control have focused on those forms that contain both estradiol and progestin-combination pills. There has also been a focus on the risks associated with synthetic estrogen, and many women choose progestin-only birth control for this reason. It is known that synthetic estrogen can increase the risk of blood clots and deep vein thrombosis.

Now, this study confirms that every form of hormonal birth control carries serious risks, which is why more women are choosing to discontinue the use of hormonal birth control.

This is the second Swedish study this year to reveal serious risks of hormonal contraception. A study published on February 12, 2025, in the British Medical Journal found that current hormonal contraceptive use doubled — and even tripled — heart attack and stroke risk. Researchers reviewed 25 years’ worth of medical records (1996-2021) from over 2 million women and found that the most popular forms of hormonal contraception, except the progestin-only (Levonorgestrel-IUD or LNG-IUD) raised ischemic stroke risk, and all but the LNG-IUD and the arm patch raised heart attack (myocardial infarction) risk. 

Why It Matters:

Research shows that teen girls and women deserve to be fully informed about the potential risks to their health when they are prescribed hormonal birth control. In addition to breast cancer, research has pointed to risks such as depression, suicidal ideation, heart attack, stroke, cervical cancer, infertility, and blood clots, depending on which hormone or hormones the woman is taking.