Research suggests a relative increase in risk, but experts say the effect is small
Epidemiological studies have been investigating for some years the possible relationship between the use of hormonal IUDs (intrauterine devices) and the risk of breast cancer — a topic that often raises questions among patients in offices and on social media. Although analyzes of large population bases indicate a statistical association between the levonorgestrel-releasing IUD and an increased risk of the disease, experts urge caution when interpreting these results.
One of the most cited studies, published in 2024 in was conducted in Denmark and analyzed data from more than 150,000 women, half of whom were hormonal IUD users. After statistical adjustments, the researchers observed a relative increase of 40% in the risk of breast cancer associated with the use of the method.
More recent work, carried out in South Korea and published in 2025 in the journal followed women aged 30 to 49 years and diagnosed pathologies that could benefit from the use of levonorgestrel. The research identified a 38% higher risk of developing breast cancer among hormonal IUD users.
However, these findings must be interpreted with caution. “Despite the relative increase demonstrated in some studies, the absolute increase is low, and these values are similar to those observed with the use of oral contraceptives or due to obesity and consumption of alcoholic beverages”analyzes oncologist Diogo Sales, from Einstein Hospital Israelita in Goiânia.
High effectiveness and long lasting
The IUD is a long-acting contraceptive method inserted into the uterus and available in two main versions: copper and hormonal. In the first case, the device releases copper ions that cause a local inflammatory reaction that is toxic to sperm, reducing their mobility and viability. The hormonal IUD releases levonorgestrel, a progestogen — a synthetic hormone with an action similar to that of progesterone — which thickens cervical mucus and alters the endometrium, making fertilization and embryo implantation difficult.
Both have high contraceptive efficacy, with a failure rate of less than 1%, and can remain in the body for several years: 3 to 5 years in the case of the hormonal IUD and up to 10 years in the copper IUD. However, the use of these devices is still relatively low in Brazil. Data from of 2019 indicate that the method was used by around 3.8% of Brazilian women, while the contraceptive pill appeared as the most common method, used by 34.1%.
Access is also limited in the public system: recent survey of showed that only 19.7% of UBS insert the device, which contributes to the low use of the method in the country.
In addition to contraception, the hormonal IUD is also used to treat gynecological conditions, especially increased uterine bleeding. It reduces the thickening of the endometrium and can avoid interventions such as surgery to remove the uterus.
Risk factors
The possible link between hormonal contraceptives and breast cancer is related to the role of sex hormones in the growth of breast cells. This is because breast tissue is sensitive to estrogen and progesterone, which regulate cell proliferation.
“Prolonged exposure to these substances throughout life can increase the likelihood of DNA duplication and, therefore, the emergence of cancer cells”explains Sales. Factors that increase the time of hormonal exposure include early menarche, late menopause or not having children.
But he is also susceptible to alcohol consumption and obesity, for example, in addition to genetics. “The risk of contraceptives is of similar magnitude to other known factors”points out the oncologist. “Based on family history, regardless of the genetic component, if you have a first-degree relative who had breast cancer, your risk increases twice. If you have two first-degree relatives who had the disease, your risk is 3 times greater than that of the general population.”
Many observational studies cannot fully control for other factors that influence the risk of developing the disease. Therefore, these percentages need to be interpreted in the context of the absolute risk of the disease. And, even in studies that looked at this context, the absolute impact was small. In the case of Denmark, between 1 and 14 additional cases of breast cancer for every 10,000 women who use the IUD.
“It can be difficult to refine the studies to the point of reaching the conclusion that the cases could have another association. So, it is worth reinforcing lifestyle changes to reduce the risk of breast cancer. This is the most important thing”advises Ilza Maria Urbano Monteiro, president of the National Specialized Commission on Contraception of FEBRASGO (Brazilian Federation of Gynecology and Obstetrics Associations).
Benefits and contraindications
The treatment dimension also needs to be included in the risk and benefit assessment of the contraceptive method. The hormonal IUD is associated with protection against endometrial cancer, for example. “There are more cases of breast cancer, but proportionally women have received worse care when it comes to endometrial cancer”reports Monteiro.
In practice, the choice must align the patient’s objectives with possible risks and contraindications, such as oncological history. In the case of the hormonal IUD, it is contraindicated for those who have already had breast cancer, as the hormone can also have systemic effects on the body. “All medication, even simple things like vitamins, have beneficial and side effects”ponders Diogo Sales. “The important thing is that people are well advised before using, question possible adverse effects and understand potential associated risks.”
This text was originally published by on March 30, 2026. The content is free for republication, the source is cited, and has been adapted to the standard of Poder360.
