The longer that women take hormonal contraceptives, the higher the chance they will develop glioma — a tumor. The risk tends to be small though, mostly because the brain tumors are exceedingly rare. It has been found that in order for a woman to have an increased chance of developing this type of tumor, she must have used hormonal contraceptives for over five years.
Hormonal contraceptives include the patch, birth control pills and intrauterine devices (IUDs) All of these types of birth control contain estrogen, which is the female sex hormone, and progestin, or both.
A study was completed on Danish women who were between 15- to 49-years-old, all of whom had been diagnosed with deadly tumors between the years of 2000 and 2009. The study showed that the women who had taken hormonal contraceptives for an extended period of time — five years or longer — were 50 percent more likely to have tumors compared to those who didn’t take the contraceptives.
Gliomas are very rare. So rare that even when the risk for the development of these tumors is doubled, the risk is still not very high. In the population of women who are at a reproductive age, including women who used hormonal contraceptive, you will find that five in 100,000 of them develop a glioma yearly.
The study performed on Danish women also showed a statistically significant association in glioma and hormonal contraceptive risk, although the benefits outweigh the risk. Such as, women who take birth control pills show a decrease in uterine and ovarian cancers.
Previous research had shown the sex hormones in birth control may actually ward off gliomas, but the research was performed on women who were past menopause.
It should also be noted that obese women who took progesterone-only pills showed a higher risk for the development of gliomas. Because of this, it is advised that estrogen-only pills not be given to women who are obese.