They have claimed that oral contraceptives reduce the risk of all sorts of cancers in women, but the fact is that we just don't know that for sure, and probably never will. Even the pill's most optimistic advocates admit that any reduction in ovarian cancer risk, for example, occurs only if the pill is taken for five or more years. Any advantage in preventing ovarian cancer might be offset by the increased incidence of breast cancer associated with prolonged contraceptive use. The American Cancer Society warns that the risk of developing breast cancer increases after birth-control pills are used, and the increased risk persists for 10 years after they are stopped. Perhaps that is why we have witnessed a such a sharp increase in the incidence of breast cancer in women over age 50 in the past 25 years.
Conclusions drawn from retrospective studies are notoriously unreliable and open to manipulation.
The only conclusion to be made regarding the health benefits of oral contraceptives is that none can be made with confidence. The naturally derived, high-dose contraceptives of the early years were better at preventing pregnancy, but there was a high price to pay, and the real debt may still be outstanding. Within the past year, several studies warned against an increased risk of cardiovascular problems in women taking these new substances. They also happen to be about half as effective in preventing pregnancy. And try as we may to correct past mistakes, we often end up making a bad situation even worse.