15.06.2 Contraception

Most oral contraceptives contain an oestrogen-like drug (oestrogen) and a progestogen combined in various doses to mimic the 28-day menstrual cycle. The oestrogen alone will inhibit ovulation, but often leads to ‘break-through’ bleeding, which can be prevented by adding a progestogen. The progestogen also decreases the production of luteinizing hormone to prevent ovulation and fertilisation.

There are many combined oral contraceptive formulations available, but the most commonly used oestrogen is ethinyl-oestradiol. Progesterone itself is not used as a contraceptive as it is not active after oral administration. Oral active progestogens commonly used in combined oral contraceptives formulations are low dose levonorgestrel and norethisterone. Probably, the most serious adverse effects associated with combined oral contraceptives in an increased risk of thrombosis and myocardial infarction especially in smokers and women aged over 25 years of age. This increased risk is related to the oestrogen rather than progestogen part of the combined oral contraceptive.

The ‘minipill’ is a progestogen-only oral contraceptive, which was designed for women with a history or thromboembolic disorders or who spoke. These progestogen-only contraceptives contain low dose levonorgestrel or norethisterone. Without the oestrogen, there is a higher risk of ‘break-through’ bleeding.