Oral Contraceptives & Cancer Risk Reduction

Combined hormonal contraception moves cancer risk in two directions at once. It lowers the risk of some cancers a lot, and for a long time. It raises the risk of others a little, and only for a while. Anyone telling you the pill simply causes cancer has dropped half the evidence. So has anyone telling you it simply prevents it.

What follows is both halves, with the absolute numbers where they exist.

Ovarian cancer. Users have a 30 to 50 percent lower risk than non-users. The protection grows the longer you use it. It carries on for up to 30 years after stopping. This is one of the largest and most lasting protective effects known for any widely used medication.

Endometrial cancer. Risk drops by at least 30 percent. Again, longer use means a bigger drop, and the protection lasts for many years after stopping.

Colorectal cancer. Use is linked to 15 to 20 percent lower risk.

These are not small or short-lived findings. They are also the part most often left out of news coverage.

Breast cancer. Across all users, risk is about 7 percent higher. Among current users it is about 24 percent higher, and that figure does not shift much with how long you have used it. Risk falls after stopping. NCI states that no increase is evident by 10 years after use has ended. A large Danish study found a roughly 20 percent increase for current and recent users. Depending on the exact formulation, that ranged from none at all up to 60 percent.

The absolute version is the one to hold onto. ACOG translates the Danish findings into one extra invasive breast cancer for every 7,690 women using hormonal contraception for a year. For women under 35 it is about one per 50,000, because baseline breast cancer risk at younger ages is very low.

Cervical cancer. Risk rises with how long you use it. It is about 10 percent higher with less than 5 years of use. It is about 60 percent higher with 5 to 9 years. With 10 or more years it is roughly doubled. Risk falls after stopping. Here is the essential context: persistent high-risk HPV infection is the necessary cause of cervical cancer. So HPV vaccination and keeping up with cervical screening do far more than any contraceptive decision.

IARC classifies combined oestrogen-progestogen contraceptives in Group 1. It is worth knowing exactly what that means, because out of context it looks alarming.

Group 1 answers one narrow question. Is the evidence strong that this can cause cancer in people? For combined oral contraceptives, the answer is yes — based, IARC says, on raised risk of breast cancer among current and recent users only, of cervical cancer, and of liver cancer in populations at low risk of hepatitis B. That is all the label asserts. It is a statement about scientific certainty, not about how much risk anyone carries. And it makes no attempt to weigh that against the protection the same monograph records: IARC states there is convincing evidence these agents protect against cancer of the endometrium and ovary.

That is why a Group 1 classification should never be read as a recommendation for or against using something.

This is a conversation with a clinician who knows your history. It is not a decision to make from a fact sheet. Nothing here is a reason to start or stop a medication on your own.

Bring the things that shift the balance. Your family history of breast and ovarian cancer. Whether you carry a known cancer predisposition variant. Your age. Whether you smoke. Your cervical screening and HPV vaccination status. And which method you are actually considering, since most of this evidence comes from combined oral contraceptives rather than from IUDs, implants or progestogen-only methods.

Bring the non-cancer side too, because it is part of the same decision. That means how well the method prevents pregnancy, clot risk, bleeding, cycle control, and endometriosis or PCOS symptoms. It also means the health risks of an unintended pregnancy, which ACOG notes are greater than the breast cancer risk described here.

ACOG's overall framing is worth ending on. Hormonal contraceptives protect against ovarian, endometrial and colon cancers. So overall cancer risk may be slightly lower in users than in non-users. That does not make the breast and cervical findings unimportant. It makes them one part of a balance you get to weigh with someone who knows your situation.

• ACOG — Practice Advisory: Hormonal Contraception and Risk of Breast Cancer
• IARC Monographs — Combined Estrogen–Progestogen Contraceptives (Volume 100A)
• IARC — Agents Classified by the IARC Monographs