Cancer remains one of the leading causes of death worldwide, and in women, breast cancer is the most commonly diagnosed form. Its risk can be influenced by a range of factors including genetics, lifestyle, obesity, delayed childbirth, and prolonged hormone exposure. Over the past few decades, doctors have observed a steady rise in breast cancer cases, prompting scientists to look more closely at the potential role of medications that affect hormone levels, including the oral contraceptive pill, used daily by millions of women across the globe.Now, a massive study of more than two million women has confirmed a “statistically significant” link between hormonal contraceptive use and an increased risk of developing breast cancer. Published inJAMA Oncology, the research found that women who used progestin-only pills, containing the hormone desogestrel, faced a 21% higher risk of breast cancer, while those on combination pills with both estrogen and progesterone showed a 12% increase.

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These contraceptive pills are primarily used to prevent pregnancy by stopping ovulation, thickening cervical mucus, and thinning the uterine lining to make it harder for sperm to reach or fertilise an egg. In addition, many women take hormonal birth control to regulate menstrual cycles, reduce acne, and manage conditions such as endometriosis and polycystic ovary syndrome (PCOS).

What the study found about breast cancer and contraceptive pills

Researchers analysed data from more than two million women across multiple countries, making it one of the largest investigations of its kind.

The findings revealed that progestin-only pills, often known as the minipill, showed a stronger association with breast cancer risk compared to combination contraceptives.“The finding that desogestrel may increase breast cancer risk more than other progestins is novel,” the study authors wrote, adding that estrogen might actually reduce some of the harmful effects of progestin. This may explain why combination pills appear to carry a smaller relative risk.

How hormonal contraceptives work

The minipill prevents pregnancy by thickening cervical mucus to block sperm, suppressing ovulation, and thinning the uterine lining to prevent implantation. Combination pills achieve the same results but include estrogen, which helps regulate menstrual cycles and may offset some of the progestin’s biological effects.Women are often prescribed the minipill if they cannot take estrogen, such as those who are breastfeeding or have cardiovascular risks. The study’s authors noted that these women may need more targeted counselling about their contraceptive options, given the findings.

Experts urge balance and informed choice

Despite the confirmed link, researchers emphasised that the absolute risk remains small. For most women, the increased risk translates to a few additional cases per 100,000 each year. The authors urged women not to stop using birth control without consulting their doctors.They also highlighted the well-documented benefits of hormonal contraceptives, which include reduced risks of ovarian and endometrial cancers and effective prevention of unintended pregnancies, a major factor in lowering maternal mortality.The study concluded that women should discuss their individual health profiles with medical professionals before making contraceptive choices. “These findings should be considered in the broader context of the pill’s benefits,” the authors wrote, adding that informed, personalised counselling remains the key to safe and effective reproductive health decisions.