Contraception encompasses methods used to prevent pregnancy by interfering with one or more stages of reproduction, including ovulation, fertilisation, sperm transport or implantation-related processes depending on the method and its mechanism. Methods include barrier contraception, hormonal contraception, intrauterine contraception, permanent contraception and fertility-awareness approaches. Hormonal contraceptives can contain combined oestrogen and progestogen or progestogen alone, while non-hormonal methods include condoms, copper intrauterine devices and some fertility-awareness methods.
Contraceptive effectiveness depends not only on the intrinsic effectiveness of a method but also on correct and consistent use, continuation, method access and biological factors. Contraception is therefore a broad category rather than a single treatment. It should also be distinguished from protection against sexually transmitted infections, because most contraceptive methods do not provide that protection, whereas condoms can reduce transmission risk when used correctly but do not eliminate it.
Hormonal contraception primarily prevents pregnancy by suppressing ovulation, thickening cervical mucus and altering the endometrium, with the relative contribution of each mechanism depending on the method. Combined oral contraceptives, patches and vaginal rings contain both an oestrogen and a progestogen, while progestogen-only pills, implants, injections and hormonal intrauterine systems use progestogen-based mechanisms. Long-acting reversible contraception includes implants and intrauterine methods that provide sustained protection without requiring daily adherence. These methods can be particularly useful when avoiding frequent user-dependent actions is important. Hormonal contraception can also alter menstrual bleeding, reduce dysmenorrhoea and improve some hormone-sensitive symptoms, although benefits and side effects vary between individuals and products.
Intrauterine contraception includes copper and hormonal devices. A copper intrauterine device releases copper ions that interfere with sperm function and fertilisation and provides highly effective, long-duration contraception without systemic hormones. A hormonal intrauterine system releases a progestogen locally within the uterus, thickening cervical mucus and producing endometrial changes while providing highly effective contraception. Both are inserted into the uterus by a trained healthcare professional and can be removed when pregnancy is desired. Intrauterine methods can be used by people who have and have not previously given birth, subject to individual clinical assessment. Their effectiveness is relatively independent of daily adherence once correctly positioned, although insertion, expulsion, perforation and infection-related considerations require appropriate clinical care.
Barrier contraception works by physically or chemically reducing the likelihood that sperm reaches an egg. External and internal condoms create a physical barrier, while diaphragms and cervical caps cover the cervix and are generally used with spermicide in relevant systems. Condoms have the additional public-health role of reducing transmission of many sexually transmitted infections, although protection varies by infection and depends on correct use.
Permanent contraception includes procedures such as tubal occlusion or vasectomy, which are intended as long-term or permanent methods and therefore require careful consideration because reversal is uncertain or may not be possible. Fertility-awareness methods involve identifying the fertile window and avoiding unprotected intercourse during that period, but effectiveness depends heavily on accurate observation, interpretation and consistent adherence.
Contraceptive effectiveness is often expressed through perfect-use and typical-use concepts. Perfect use assumes the method is used exactly as instructed, whereas typical use reflects how the method performs in real-world conditions where missed pills, delayed injections, incorrect condom use or discontinuation can occur. Long-acting methods are less dependent on daily or per-act adherence and therefore can have a smaller difference between theoretical and real-world effectiveness.
Effectiveness can also be affected by drug interactions, gastrointestinal absorption in some oral methods, timing of initiation and, for intrauterine devices, correct placement. No contraceptive method is completely free of failure. Accurate counselling therefore requires discussion of both effectiveness and practical suitability rather than treating a single effectiveness figure as universally predictive for every user.
Contraceptive choice can be influenced by age, reproductive goals, medical history, medications, bleeding preferences, ability to adhere to a regimen, convenience, reversibility and personal circumstances. Some oestrogen-containing methods are unsuitable for people with particular conditions or risk factors, such as certain histories of thrombosis or migraine patterns, while progestogen-only methods have different eligibility considerations. Clinical guidance uses structured eligibility criteria to determine which methods can be used safely in different circumstances.
Contraceptive counselling should also consider the possibility of sexually transmitted infections, because a person may require condoms alongside another contraceptive method. Shared decision-making is important because a highly effective method that a person cannot or does not wish to use consistently may be less useful in practice than another suitable method that can be maintained reliably.
Contraception has social and public-health significance because preventing unintended pregnancy can influence maternal health, reproductive autonomy, family planning, educational and employment opportunities and use of healthcare resources. Access depends on availability of services, affordability, geographic factors, information, confidentiality and cultural or social circumstances. Contraceptive services may include counselling, prescription, device insertion and removal, follow-up and management of side effects. Myths can arise around fertility after contraception, weight change, infertility and long-term reproductive effects, but the validity of any claim depends on the specific method. Most reversible contraceptive methods do not cause permanent infertility, and fertility generally returns after discontinuation at a rate determined by the method and individual biology.
Contraception should be distinguished from emergency contraception, which is specifically intended to reduce pregnancy risk after unprotected intercourse or contraceptive failure and is used within defined time windows. It should also be distinguished from abortion, which ends an established pregnancy rather than preventing fertilisation or preventing pregnancy from becoming established. Contraceptive methods differ in mechanism, duration, reversibility, user dependence, side effects, non-contraceptive benefits and protection against sexually transmitted infections. A comprehensive understanding of contraception therefore requires consideration of biological mechanisms and practical use together. The central purpose is pregnancy prevention, but method selection encompasses effectiveness, safety, acceptability, reproductive intentions and access to appropriate healthcare.
