Growing up with three older sisters who were more than ten years older than me, I became fascinated with the connection I saw between women’s hormones and their mood. One of my sisters had such severe mood swings around her period that just asking her where she wanted to eat could send her into a hurling spiral of anger and meanness. As an adult, I was intrigued to learn that taking birth control pills could reduce period-related mood swings and that it had other beneficial effects on mental health, like decreased likelihood for depression. I found that women and their doctors were already clued in to these and its other beneficial side effects, like treating acne or reducing painful periods; for decades, women have commonly taken the pill, sometimes even exclusively, for reasons other than to prevent pregnancy.

Despite the connection I noticed with my sister’s mood swings and her relationships, I was surprised to discover that no studies had examined whether the pill and its mood stabilizing effect had an impact on women’s relationships. So, I wondered, could higher relationship satisfaction be an additional, albeit unexpected, side effect of taking the pill?

Monthly fluctuations in reproductive hormones are associated with changes in mood as well as various mood and anxiety disorders. For instance, decreased estrogen levels are associated with negative mood and depression, and increases are associated with mood enhancement. Birth control pills work to prevent pregnancy essentially by blocking these fluctuations. Though still unclear, scientists largely believe this stabilization of hormones is responsible for the positive effects to women’s mental health.

I surveyed hundreds of women across the United States and asked them if they used birth control pills, how frequently and severely they experienced mood swings, and how satisfied they were with their romantic relationship. Consistent with my predictions, I found that women using the pill had: (1) fewer and less intense mood swings and (2) higher satisfaction with their relationship than women who did not use the pill. To understand this relationship better, I used a complex statistical procedure to test whether pill user’s higher relationship satisfaction was due to their reduction in mood swings. Indeed, my tests revealed that pill users were significantly more satisfied with their relationships than non-users because of the reduction in mood swings due to pill use. This means that the pill—one of the most commonly taken prescription medications—has the potential to affect not only how the user is feeling, but also how others feel around them. Though additional research is required to verify this, our findings suggest that the pill may be a particularly useful treatment option for women who struggle with mood swing symptoms and interpersonal problems around their period.