Millions of women around the world have used the combined oestrogen and progestogen oral contraceptive pill to protect themselves from pregnancy for more than fifty years. The overall risk of reproductive-aged women developing cancer is low, but debate continues as to whether using the pill could increase this risk.
In fact, fear of cancer has been identified as a major reason for women not using reliable contraceptive methods.
Women’s risk of developing cancer depends on a large number of factors, including family history, cigarette smoking, weight, diet and physical activity and whether you’ve had children (and at what age), among other things.
The pill works by effectively switching off a woman’s natural production of ovarian oestrogen and progesterone and replacing this with a synthetic version of both hormones.
A change in cancer risk associated with the pill could potentially be related to the synthetic hormones within the pill. But it could also be due to the fact that the ovaries have been “shut down” for a period of time. It’s likely a range of determinants are involved.
Researchers’ attempts to assess any link between the pill and cancer are complicated by a number of factors.
Firstly, women have access to a wide variety of contraceptive pills, which have different oestrogen and progestogen components, doses of hormones, and schedules of delivery. Some pills have a stable dose; others vary throughout the cycle. The original contraceptive pill also had much higher doses of hormones than the modern pill. So there’s no standard “pill” researchers can use to generalise cancer risk.
Secondly, many women have taken a variety of contraceptive pills throughout their lifetime. This makes recalling the type of pill – and the duration of the prescription – difficult. And this creates some uncertainties in the research.
So what does the research say?
Despite concerns that the pill increases the risk of cancer, systematic studies have found the incidence of some cancers is actually reduced in women taking the pill.
Numerous studies confirm that taking the pill is associated with a [reduced risk of ovarian cancer](http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(08)60167-1/fulltext ). This protective effect is greater the longer one uses the pill, and extends for several years after use is ceased.
Multiple studies have also found a 50% reduction in the risk of endometrial cancer for women taking the pill, which is still apparent for ten to 20 years after use has ceased.
A study of more than 300,000 European women reported a decrease in colorectal cancer in women who had ever used the pill, but the effect was only significant amongst postmenopausal women.
The studies for breast cancer and the pill report conflicting findings. Most [researchers](http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(96)90806-5/abstract) have concluded there is no significant link between previous or current use of the pill and breast cancer risk. But some studies suggest a slightly increased risk for current pill users, which disappears five to ten years after a woman stops taking the pill.
Using an oral contraceptive for more than five years has also been linked to an [increased incidence of cervical cancer](http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(07)61684-5/fulltext). Again, this additional risk decreases with time after a woman stops taking the pill and has disappeared within ten years of cessation.
So, what does this all mean for women taking the pill?
Be reassured that if you’re at low risk of cancer, the pill is unlikely to place you at higher risk – and may even protect you against some cancers after your reproductive years end.
But every woman’s risk profile is different. When you discuss your contraceptive choices with your doctor, be sure to ask about your specific risks and benefits associated with the pill.