Using nuclear magnetic resonance imaging, which makes three-dimensional pictures of the brain, the scientists were able to demonstrate that the birth control pill is able to change the size of parts of the brain - but only by a few percent.
However, even these minimal changes were shown to have an impact. The part of the brain responsible for facial recognition increased in size in some of the women who took part in the study. Neuropsychologist Belinda Pletzer found that some of the women taking the contraceptive pill were able to remember unfamiliar faces better than women who didn't take the pill.
Taking the pill could also have more long-term consequences on women's choices. "Women seem to choose different partners if they are taking the pill compared to if they weren't taking the pill,” Pletzer said.
However, she said this didn't necessarily mean that women were making better or worse choices. She said that her research made it clear that hormonal contraceptives had a measurable impact on a woman's brain and behaviour.
She plans to do further research to find out how the pill affects a woman's behaviour and development as she ages.