Are birth control pills (oral contraceptives) classified as a carcinogen?

Birth Control Pills and Carcinogen Classification

Yes, combined oral contraceptives (COCs) are classified as Group 1 carcinogens by the International Agency for Research on Cancer (IARC), though this classification must be understood in the context of their overall risk-benefit profile. 1, 2, 3, 4

Understanding the Carcinogen Classification

The IARC classification as a Group 1 carcinogen indicates that there is sufficient evidence that COCs can cause cancer in humans, specifically:

• Increased risk of breast cancer: Current COC users have a relative risk of 1.24 (95% CI, 1.15-1.33) for breast cancer, with risk returning to baseline approximately 10 years after discontinuation 5
• Increased risk of cervical cancer: Risk increases with duration of COC use, particularly with ≥5 years of use, and declines after discontinuation 5

However, this classification must be balanced against several important factors:

Cancer Risk Reduction Benefits

COCs also provide significant protective effects against certain cancers:

• Reduced risk of endometrial cancer 5, 2
• Reduced risk of ovarian cancer with protection lasting 15-20 years after discontinuation 5, 2
• Reduced risk of colorectal cancer 5, 6

Risk Stratification and Context

The absolute risk increase for most cancers is small, particularly when considering:

• Age-related factors: Breast cancer risk is highest in women <34 years when the baseline incidence is lowest 5
• Duration of use: Some cancer risks correlate with longer duration of use 5
• Time since discontinuation: Many risks diminish after stopping COCs 5

Progestin-Only Contraceptives (POCs)

POCs have a different risk profile:

• Less data is available on cancer risks compared to COCs 7
• Some evidence suggests POCs may also increase overall cancer risk, particularly for breast cancer 1
• POCs do not appear to increase the risk of venous thromboembolism 8

Clinical Decision-Making Algorithm

When considering birth control options and cancer risk:

1. Assess baseline cancer risk factors:

   • Family history of breast or reproductive cancers
   • Age (risks increase with age, particularly >35 years)
   • Smoking status (increases cardiovascular risks with COCs)

2. Consider duration of planned use:

   • Short-term use has less impact on cancer risk
   • Long-term use (≥5 years) may increase certain cancer risks

3. Evaluate alternative options:

   • For women with high baseline cancer risk, consider non-hormonal methods
   • For women with contraindications to estrogen, consider progestin-only methods

Important Caveats

• The IARC classification does not produce risk-benefit analyses for specific populations 3, 4
• The absolute risk increase for most women is small when compared to other risk factors
• Pregnancy itself carries higher risks of certain conditions (e.g., VTE risk in pregnancy is 5-20 per 10,000 woman-years compared to 3-9 per 10,000 woman-years with COCs) 5
• The WHO reports that COCs are not associated with increased risk of myocardial infarction in healthy, normotensive, nondiabetic, nonsmokers at any age 5

Conclusion

While birth control pills (specifically combined oral contraceptives) are classified as carcinogens, this classification must be interpreted within the context of their overall health impact, which includes cancer-protective effects and significant non-contraceptive benefits. The decision to use hormonal contraception should weigh these factors against individual risk factors and alternative options.