The personality traits of women who use contraceptive pills do not differ from those who don’t, according to a new study published in Psychoendocrinology. The findings strengthen previous research on the cognitive and emotional effects of hormonal contraceptives by ruling out personality as a confounding factor.

“Oral contraceptive (OC) use is an under-utilized ‘natural experiment’ for studying links between sex hormones and the human brain and behavior,” explained study author Adriene M. Beltz, an assistant professor and head of the Methods, Sex differences, and Development Lab at the University of Michigan.

“By comparing women who do and do not use ‘the pill,’ we can infer the effects progesterone, estrogen, and even androgen have on cognition and affect — as long as we use appropriate controls (e.g., for hormone-related medications and medical history). The problem is that women are not randomly assigned to pill use, so women who choose to use the pill might differ from women who do not in key ways that are also related to cognition and affect. This is a confound.”

“In fact, previous studies have specifically mentioned that differences between OC users and non-users might be due to personality characteristics instead of to neuroendocrinological processes. For this reason, we set out to examine whether women who do and do not use the pill differ in personality,” Beltz said.

The study of 632 women (ages 18-38) found no significant differences between women who were using oral contraceptives and women who were not using oral contraceptives. In addition, women who used different types of oral contraceptive pills did not differ from each other in personality.

“Women who do and do not use OCs have similar personalities, as assessed by the traditional Big Five factors of Neuroticism, Extraversion, Openness, Agreeableness, and Conscientiousness,” Beltz told PsyPost.

“Findings were replicated in two large samples, each with 6-to-10 times the number of OC users in the average OC study. Findings also strengthen the neuroendocrinological implications that can be drawn from previous work on the neural and behavioral correlates of OC use, because personality differences between users and non-users is now an unlikely alternative explanation for detected effects.”

“In other words, with personality differences ruled out, previously detected cognitive and affective differences between OC users and non-users are likely related to sex hormones,” Beltz explained.

The study — like all research — includes some limitations.

“Although our samples are representative of those commonly employed in OC research (i.e., young women from university communities), it is important for future work to examine the extent to which findings hold for more diverse samples. For instance, there is evidence that personality changes with age, so we need to examine whether OC users and non-users in middle adulthood also have similar personalities.”

The study, “No personality differences between oral contraceptive users and naturally cycling women: Implications for research on sex hormones“, was authored by Adriene M. Beltz, Amy M. Loviska, and Dominic Kelly.