Abstract
Several studies have reported that heterosexual women's preferences for male faces vary with hormonal fluctuations over the menstrual cycle and that women tend to prefer more masculine faces during ovulation or when not using hormonal contraceptives. While this has been tested using observational data, we provide the first double-blind randomized controlled study testing if oral contraceptives reduce preferences for facial masculinity and symmetry. Three hundred and forty women were randomized to either oral contraceptives or placebo and their facial preferences were measured at baseline and after 3 months. All analyses follow a pre-registered pre-analysis plan. No statistically significant effect of oral contraceptives on preferences for facial masculinity or facial symmetry was found. In pre-registered exploratory analyses, we further find no statistically significant associations between menstrual cycle phase or hormone levels and facial preferences. These results provide evidence against a causal effect of oral contraceptives on women's preferences for masculine and symmetric faces, although our results should be interpreted cautiously as we only find strong evidence against effect sizes larger than about 0.4 Cohen's d units.