This systematic review and meta-analysis examines how combined oral contraceptives affect testosterone levels in healthy women. The authors found that oral contraceptives reduce androgen levels by suppressing ovarian and adrenal androgen synthesis while also increasing sex hormone-binding globulin, which lowers free testosterone even further. This paper is especially relevant because it connects hormonal symptoms in younger women to a very common clinical exposure and helps explain why androgen insufficiency may be overlooked in otherwise healthy premenopausal patients. (OUP Academic)

In short: this meta-analysis is often cited because it demonstrates that combined oral contraceptives lower circulating androgen levels and increase SHBG, reducing free testosterone in healthy women.