1. Pharmacology of estrogens and progestogens: influence of different routes of administration
2. Faculty of Sexual and Reproductive Healthcare of the Royal College of Obstetrics and Gynaecology UK medical eligibility criteria for contraceptive use. 2016 (amended 2019), https://www.fsrh.org/documents/ukmec-2016/ (accessed 4 Oct 2021).
3. Faculty of Sexual and Reproductive Healthcare of the Royal College of Obstetrics and Gynaecology.). Progestogen only pills, 2015 (amended 2019). https://www.fsrh.org/standards-and-guidance/documents/cecceu-guidance-pop-mar-2015/ (accessed 4 Oct 2021).
4. 20 µg versus >20 µg estrogen combined oral contraceptives for contraception
5. UpToDate (2021) Combined estrogen–progestin oral contraceptives: patient selection, counselling and use, https://www.uptodate.com/contents/combined-estrogen-progestin-oralcontraceptives-patient-selection-counselingand-use (accessed 4 Oct 2021).