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Synthetic hormones used for birth control may slow brain maturation and disrupt the development of an area of the brain responsible for impulsivity, according to new research.

Adolescents commonly use hormonal contraceptives despite the unknown effects on brain and behavioral maturation, prompting scientists at Ohio State University to explore how common synthetic hormones used for birth control affect the prefrontal cortex โ€” an area of the brain essential to regulating emotional behaviors and executive function.

In the study, presented during a Nov. 12, 2023, poster session at an annual meeting of the Society for Neuroscience, researchers gave a combination of synthetic estrogen and progesterone in hormone-based contraceptives to female rats from early to late adolescence and compared their behavior and brain tissue to untreated rats.

Because synthetic hormones found in contraceptives decrease the ovaries' production of natural progesterone and estrogen to prevent ovulation, researchers looked at how the brain is affected by these hormonal differences when it is still developing.

The study concentrated on myelination and microglia โ€” immune cells that โ€‹โ€‹regulate brain development, maintenance of neuronal networks, and injury repair โ€” because both play essential roles in prefrontal cortex development. Myelination plays a role in the development of the prefrontal cortex and involves the formation of a protective coating called the myelin sheath around nerves to improve conduction.

Myelination in the human central nervous system begins one to two months before birth and persists into the third decade of life โ€” consistent with the time it takes for cognitive function in children and adolescents to develop. According to the study, myelination is mediated by the same hormones that hormonal contraceptives target.

Since synaptic development and myelination during the adolescent window are sensitive to the onset of hormones during puberty, the authors theorized that disrupting hormonal activity during puberty could "potentially shift the trajectory of some of those developmental processes," co-senior author Kathryn Lenz, associate professor of psychology at Ohio State, said in a news release.

"When it comes to nervous system communication, keeping it steady is key โ€” too much or too little can lead to dysfunction that affects the mood and behavior," she said.

The study found myelination increased and microglia decreased when the rats were given hormonal contraception, indicative of disrupted communication. In behavioral threat appraisal tests, rats given hormonal contraceptives were found to be more likely to engage in risk-taking behaviors, such as remaining in elevated wide-open spaces and sampling treats in unfamiliar settings.

Lab tests confirmed that the synthetic ethinyl estradiol and levonorgestrel given to the treated rats were present in brain tissue. However, researchers were unable to determine if the effects were due to how synthetic hormones shut down natural hormone production or if they were directly impacting the brain.

The study provides some of the first evidence showing that hormonal contraceptives given during the vulnerable developmental period of adolescence may influence the development of the prefrontal cortex, contributing to altered risk-assessment behavior.