Women who take birth control pills have a smaller hypothalamus, a region of the brain associated with mood and sex drive, compared to non-users, according to preliminary research.
The findings are based on brain scans of 50 healthy women, including 21 women who were taking oral contraceptives.
But the researchers say having a smaller hypothalamus did not affect cognitive performance or behaviour.
Dr Michael Lipton, professor of radiology at Albert Einstein College of Medicine in New York, said: “We found a dramatic difference in the size of the brain structures between women who were taking oral contraceptives and those who were not.
“This initial study shows a strong association and should motivate further investigation into the effects of oral contraceptives on brain structure and their potential impact on brain function.”
The researchers said they also found a “strong correlation” between smaller hypothalamic volume and greater anger and depressive symptoms.
The results were presented at the Radiological Society of North America’s annual meeting and have not been published in an academic journal.
But experts say these findings should be presented with caution.
Commenting on the research, Christopher Petkov, a professor of comparative neuropsychology at Newcastle University, said: “I would be very careful about concluding that oral contraceptive use is associated with smaller hypothalamic volumes from this preliminary work being presented at a scientific meeting for the authors to discuss with the scientific community as they work towards completing their study.”
Derek Hill, a professor of medical imaging at University College London, added: “Results like this are intriguing but must be treated with caution.
“In order for these results to be more conclusive, it would be necessary to undertake further research on more women, including looking at the same women before and after they take the pill, and after they come off the pill, to look for some evidence of whether the change is caused by the medicine, and whether or not it is reversible.”