The next time you think of popping a birth control pill think again as a new study reveals that the long-term use of hormonal contraceptives heightens the risk of brain tumors.

Researchers from Denmark observed Danish women aged between 15 to 49 years and reveal that taking hormonal contraceptives for nearly five years increases the probability of women developing glioma of the brain, a type of rare brain tumor. The use of such contraceptives doubles the risk of brain tumor per the study.

Any form of hormonal contraceptive contains female sex hormones. While little is known as to what causes glioma, there is evidence to support the belief that female sex hormones could heighten the risk of certain types of cancers. On the other hand, there is also proof that the use of contraceptives may decrease the risk of cancer in some age groups.

Prompted by these factors, the researchers led by Dr. David Gaist (of Odense University Hospital and University of Southern Denmark) looked to evaluate whether the use of hormonal contraceptives played a role in increasing the risk of gliomas in women of a certain age who used them.

For the purpose of the study, the researchers observed data from the national administrative and health registries in Denmark. They identified 317 women who had been diagnosed for glioma between 2000 and 2009. Each of these women was compared with eight other women in the same age bracket who did not suffer from glioma.

So what did the researchers find?

"A nearly two-fold increased risk of glioma was observed among long term users of hormonal contraceptives," wrote the authors in the study.

The researchers also found a "moderately increased risk of glioma" in women who were younger and had deployed hormonal contraceptives. The researchers also revealed that Progestogen-only contraceptives were linked with a higher risk of glioma - nearly three-fold.

"In a population of women in the reproductive age, including those who use hormonal contraceptives, you would anticipate seeing 5 in 100,000 people develop a glioma annually, according to the nationwide Danish Cancer Registry," notes Dr. Gaist.

The findings have been published in the British Journal of Clinical Pharmacology.