Combined Oral Contraceptive Pills
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Direct answer
Combined oral contraceptive pills contain an oestrogen, usually ethinyl estradiol, and a progestin that together suppress FSH and LH to prevent ovulation. They also thicken cervical mucus and thin the endometrium, and their main serious risk is venous thromboembolism, which limits use in women with migraine with aura and other absolute contraindications.
What you must remember
- Formulations: Monophasic, biphasic and triphasic packs, with ethinyl estradiol in the range of 20 to 35 micrograms in most products.
- Progestins: Levonorgestrel, norethisterone, desogestrel, drospirenone and cyproterone acetate, each with a different androgenic or anti-androgenic profile.
- Mechanism: Suppression of FSH and LH prevents follicular development, while cervical mucus thickens.
- Non-contraceptive benefits: Regular, lighter menses, less dysmenorrhoea, fewer functional ovarian cysts, and reduced acne or hirsutism in PCOS with appropriate progestins.
- Cancer protection: Long-term use lowers ovarian and endometrial cancer risk, and this protection persists for years after stopping.
- Serious risk: Venous thromboembolism, increased by smoking, obesity, age above 35 and a personal history of thrombosis.
- Absolute contraindications: Migraine with aura, past deep vein thrombosis or pulmonary embolism, known thrombogenic mutation, current breast cancer, heavy smoking after age 35 and uncontrolled hypertension.
Comparing the progestins
Choosing a formulation depends on the clinical goal, and the progestin largely determines the androgenic profile.
| Progestin | Androgenic effect | Typical use |
|---|---|---|
| Levonorgestrel | Relatively androgenic | Standard monophasic packs |
| Norethisterone | Relatively androgenic | Common lower-cost packs |
| Desogestrel | Low androgenic | Users prone to acne or hirsutism |
| Drospirenone | Anti-mineralocorticoid and anti-androgenic | PCOS-related acne or hirsutism |
| Cyproterone acetate | Anti-androgenic | Hirsutism and acne with ethinyl estradiol |
The table shows general tendencies rather than strict rules. The oestrogen dose and the venous thromboembolism risk apply to all formulations, so the progestin does not remove the need for screening.
Screening before prescribing is a checklist of age, smoking, blood pressure, migraine history, family history of clots and breast cancer history. These checks decide between a combined pill and a progestin-only alternative, and they are repeated at follow-up.
A woman with a family history of clots should be assessed for inherited thrombophilia before a combined pill is started, because the risks add together.
Where the exam tries to catch you
Combined pill questions usually turn on a single absolute contraindication, and the trap is often a patient who seems otherwise healthy.
- Trap: Continuing the pill after migraine with aura develops. Correct: Migraine with aura is an absolute contraindication because it raises ischaemic stroke risk, so progestin-only methods are preferred.
- Trap: Assuming the pill is safe in a smoker aged 35 or older. Correct: Heavy smoking after age 35 is an absolute contraindication due to cardiovascular risk.
- Trap: Starting an oestrogen-containing pill in the early postpartum period. Correct: Oestrogen is avoided early after delivery because venous thrombosis risk is high in that window.
Frequently asked questions
Which hormones are present in combined oral contraceptive pills?
Combined oral contraceptive pills contain an oestrogen, usually ethinyl estradiol, and a progestin such as levonorgestrel, norethisterone, desogestrel, drospirenone or cyproterone acetate. The progestin largely determines the androgenic profile and side effect pattern.
Is migraine without aura a contraindication to combined oral contraceptives?
Migraine without aura is generally not a contraindication to combined oral contraceptive pills. Migraine with aura, however, is an absolute contraindication because the oestrogen component raises the risk of ischaemic stroke, and progestin-only methods can be considered instead.
Why do combined oral contraceptives reduce ovarian cancer risk?
Combined oral contraceptives reduce ovarian and endometrial cancer risk, largely by suppressing ovulation over prolonged use. The protective effect persists for years after stopping, which is one of the recognised non-contraceptive benefits.
What is the main serious risk of combined oral contraceptive pills?
The main serious risk of combined oral contraceptive pills is venous thromboembolism, which the oestrogen component increases. Smoking, obesity, age above 35 and a history of thrombosis raise the risk, so these factors are screened before prescribing.