Hormonal Contraception

Hormonal contraception uses synthetic oestrogens and progestogens to prevent pregnancy, principally by suppressing ovulation and altering the cervical mucus and endometrium. It includes combined and progestogen-only pills, injectables, patches, vaginal rings, and subdermal implants, ranging from short-acting daily methods to long-acting reversible options.

Definition

Hormonal contraception is the prevention of pregnancy through exogenous steroid hormones (oestrogens and/or progestogens) delivered orally, transdermally, vaginally, by injection, or by implant, which act mainly by inhibiting ovulation and modifying the cervical mucus and endometrium.

Scope

This entry covers the hormonal mechanisms of contraception, the distinction between combined oestrogen-progestogen and progestogen-only methods, the spectrum from daily pills to long-acting implants, and the principal safety consideration of venous thromboembolism risk with oestrogen-containing methods. It is a reference overview of how these methods work and how their effectiveness and risks are studied, not prescribing guidance.

Core questions

• How do combined and progestogen-only methods differ in mechanism and eligibility?
• Why does the route and duration of delivery affect typical-use effectiveness?
• How is the venous thromboembolism risk of oestrogen-containing methods weighed against benefits?

Key concepts

• Combined oral contraceptive (oestrogen plus progestogen)
• Progestogen-only pill
• Ovulation suppression
• Cervical mucus thickening
• Subdermal implant
• Venous thromboembolism risk
• Typical-use versus perfect-use failure

Mechanisms

Combined methods deliver an oestrogen and a progestogen that suppress pituitary gonadotropin secretion, preventing the mid-cycle luteinizing-hormone surge and thereby inhibiting ovulation; the progestogen component additionally thickens cervical mucus to impede sperm and renders the endometrium less receptive. Progestogen-only methods rely more on cervical-mucus and endometrial effects with variable ovulation suppression depending on the agent and dose. Long-acting implants release progestogen steadily for years, achieving very low failure rates because effectiveness does not depend on daily adherence, as documented by Winner and colleagues (2012). Oestrogen-containing methods carry a modestly increased risk of venous thromboembolism, reviewed by Morimont and colleagues (2021) and quantified in the cohort study of Lidegaard and colleagues (2009).

Clinical relevance

Hormonal methods are among the most widely used reversible contraceptives, and clinicians match them to individual health profiles using frameworks such as the World Health Organization medical eligibility criteria, which flag conditions where oestrogen-containing methods may be inadvisable. This entry explains the mechanisms and the evidence on effectiveness and risk at a reference level and does not provide individual prescribing or dosing advice.

Epidemiology

Trussell (2011) reports that combined and progestogen-only pills have a perfect-use failure rate of roughly less than one percent but a higher typical-use failure rate because of missed doses, whereas implants achieve very low typical-use failure rates. Cohort data from Lidegaard and colleagues (2009) show an absolute venous thromboembolism risk that is low overall but elevated relative to non-users, varying by progestogen type and oestrogen dose.

History

The first combined oral contraceptive was approved in 1960, transforming reproductive health by separating contraception from the act of intercourse. Subsequent decades brought lower-dose oestrogen formulations to reduce thromboembolic risk, progestogen-only options for those who cannot take oestrogen, and long-acting implants that extended the effectiveness advantages of hormonal contraception to multi-year, user-independent delivery.

Debates

How large is the venous thromboembolism risk of newer progestogens?

Cohort and review evidence suggests combined pills containing certain newer progestogens may carry a somewhat higher venous thromboembolism risk than those with older progestogens, though the absolute risk remains low and the comparisons are debated because of confounding and prescribing patterns.

Seminal works

• trussell-2011
• winner-2012
• lidegaard-2009

Frequently asked questions

How do hormonal contraceptives prevent pregnancy?

They mainly suppress ovulation by inhibiting the hormonal signals that trigger egg release, and they also thicken cervical mucus and alter the endometrium; progestogen-only methods rely more on the cervical-mucus and endometrial effects.

Why are implants more effective in typical use than pills?

Implants release hormone continuously for years and do not depend on the user remembering a daily dose, so their typical-use failure rate is far lower than that of pills, which can fail when doses are missed.