The classification of birth control as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC) can be concerning. This designation, while important for scientific understanding, requires a clear explanation to avoid misinterpretations about individual risk. Understanding what this classification means in a broader context is helpful for those seeking informed health decisions.
Understanding Group 1 Carcinogen Classification
The International Agency for Research on Cancer (IARC), a part of the World Health Organization (WHO), classifies agents based on scientific evidence indicating their ability to cause cancer. A “Group 1 carcinogen” designation means there is sufficient evidence that the agent causes cancer in humans. This classification focuses on the hazard itself, indicating potential to cause cancer under some circumstances, not the level of risk or common exposure.
Many common substances and exposures are also classified as Group 1 carcinogens. Examples include alcoholic beverages, processed meat, solar radiation, and human papillomavirus (HPV). This grouping highlights that while these agents can cause cancer, the actual risk to an individual depends on factors like the level and duration of exposure. The IARC’s classification system evaluates the strength of evidence, not the magnitude of risk.
Birth Control Methods and Cancer Links
The IARC classification of combined oral contraceptives (COCs) as Group 1 carcinogens was established in 2012, building on earlier assessments. These contraceptives have been linked to an increased risk of certain cancers, including breast cancer and cervical cancer. Studies have shown that combined oral contraceptives can cause cancer of the breast, as well as in situ and invasive cancer of the uterine cervix. There is also some evidence suggesting a link to liver cancer, though recent studies have provided less support for this connection, potentially due to differences in populations studied, such as those in areas with endemic hepatitis. While the classification primarily focuses on combined oral contraceptives, some recent literature also suggests that progestin-only contraceptives, such as implants and vaginal rings, may also increase the risk of breast and cervical cancer.
Magnitude of Cancer Risk
While combined oral contraceptives are classified as Group 1 carcinogens, it is important to understand the actual magnitude of the increased cancer risk. For breast cancer, women currently using or who have recently stopped using combined oral contraceptives experience a modest increase in risk, approximately 20% compared to those who have never used them. This increase can range from 0% to 60% depending on the specific type of combined oral contraceptive. This increased risk of breast cancer generally declines after discontinuing use, returning to baseline levels within about 10 years.
For cervical cancer, women who have used oral contraceptives for five or more years face a higher risk than non-users. One study found a 10% increased risk for less than five years of use, a 60% increase for five to nine years of use, and a doubling of risk with 10 or more years of use. The link between the combined pill and cervical cancer may be influenced by the duration of use and typically diminishes within 10 years after stopping.
Balancing Risks with Protective Effects and Benefits
Hormonal birth control, particularly combined oral contraceptives, offers significant protective effects against other types of cancer. These methods are associated with a reduced risk of ovarian cancer and endometrial (womb) cancer. The protective effect against ovarian cancer can be substantial, with the risk decreasing by approximately 20% for every five years of use and around 50% for 15 years of use. This protection can last for decades after discontinuing use, even up to 30 years.
Similarly, combined oral contraceptives can significantly lower the risk of endometrial cancer, with a risk reduction of about 30% to 40% in broad epidemiological studies. This protective effect can persist for many years after stopping the pill, potentially for over 30 years. Beyond cancer protection, hormonal birth control offers numerous non-contraceptive health benefits:
Regulating menstrual periods
Treating irregular or heavy periods
Alleviating painful periods associated with endometriosis
Managing symptoms of polycystic ovary syndrome (PCOS)
Improving acne
Reducing hirsutism by affecting hormone levels