Contraceptive pills may affect women's brains, impairing the part that regulates fear, a study has found.

The study found that the ventromedial prefrontal cortex (vmPFC), the part of the brain associated with emotion regulation, including fear and anxiety extinction, was thinner in women who used combined oral contraceptives compared to men.

Combined oral contraceptives are birth control pills that contain estrogen and progestin. The pills work by preventing ovulation and changing mucus in the cervix and uterus lining, thereby preventing the fusion of sperm with the egg. Apart from preventing pregnancies, these types of pills are used in the treatment of dysmenorrhea (painful periods), irregular or heavy periods and endometriosis.

The findings of the latest study were published in the Frontiers in Endocrinology.

Researchers believe the effect on the brain area is reversible once the birth control pills are stopped, as the changes in brain morphology were not evident in those who had used them in the past. However, more research is required to confirm how long the effect lasts.

"In our study, we show that healthy women currently using COCs had a thinner ventromedial prefrontal cortex than men. This part of the prefrontal cortex is thought to sustain emotion regulation, such as decreasing fear signals in the context of a safe situation. Our result may represent a mechanism by which COCs could impair emotion regulation in women," study first author Alexandra Brouillard, from Université du Québec à Montréal, Canada, said in a news release.

Studies have shown that women are more susceptible to experiencing anxiety and stress-related disorders than men. To determine the impact of exogenous hormones (found in contraceptive pills) and endogenous hormones (naturally occurring in the body) on fear-related brain morphology, the team evaluated women who currently use the birth control pills, those who used them previously, and who have never used any form of hormonal contraception, and compared it with men.

"As we report reduced cortical thickness of the ventromedial prefrontal cortex in COC users compared to men, our result suggests that COCs may confer a risk factor for emotion regulation deficits during their current use," Brouillard said.

The study has not established a causative link between pill usage and changes in brain morphology. Researchers say the behavioral and psychological impact of the pills cannot be established based on the anatomical findings.

"The objective of our work is not to counter the use of COCs, but it is important to be aware that the pill can have an effect on the brain. Our aim is to increase scientific interest in women's health and raise awareness about early prescription of COCs and brain development, a highly unknown topic," Brouillard added.