Contraception

Introduction

Choosing a contraceptive method involves balancing efficacy, the patient's medical history and personal preferences, side effects, and non-contraceptive benefits (such as cycle control or reduced menstrual bleeding). No single method suits everyone, and part of the clinical skill is matching options to the individual rather than defaulting to the most commonly prescribed method.¹

UK prescribing is guided by the UK Medical Eligibility Criteria for Contraceptive Use (UKMEC), which grades each method from 1 (no restriction) to 4 (unacceptable health risk) against a long list of medical conditions and characteristics, giving a structured, evidence-based way to assess safety for an individual patient.²

Effectiveness overview

Efficacy is described with 'perfect use' (theoretical maximum effectiveness with correct, consistent use) and 'typical use' (effectiveness accounting for real-world imperfect use) failure rates. The gap between the two is largest for user-dependent methods and smallest for long-acting reversible contraception (LARC) - implants, intrauterine devices/systems and injectables - which is why LARC methods are consistently the most effective in practice, not just in theory.³

Combined hormonal contraception

Combined hormonal contraception (oestrogen plus a progestogen) is available as a pill (COC), patch, or vaginal ring. It works primarily by inhibiting ovulation through suppression of the hypothalamic-pituitary-ovarian axis, with additional effects on cervical mucus and the endometrium.¹ Benefits include reliable, predictable cycle control, reduced menstrual bleeding and dysmenorrhoea, and a reduction in ovarian and endometrial cancer risk that persists for years after stopping.

The main safety concern is a small absolute increase in the risk of venous thromboembolism (VTE), attributable to the oestrogen component, along with a small increase in arterial event (stroke, myocardial infarction) risk in those with additional risk factors.²

Progestogen-only methods

Progestogen-only pill (POP)

Traditional POPs primarily thicken cervical mucus and must be taken within a strict 3-hour window each day; the desogestrel-only pill additionally and reliably inhibits ovulation in most users and has a more forgiving 12-hour window, making it the preferred POP in most guidance now.¹ The POP is a useful option where oestrogen is contraindicated, including in breastfeeding, migraine with aura, and most cardiovascular risk factors, and has no upper age or smoking-related restriction.

Injectable contraception

Depot medroxyprogesterone acetate, given by intramuscular or subcutaneous injection every 13 weeks, works by inhibiting ovulation. Irregular bleeding is common initially, often settling to amenorrhoea with continued use. A recognised concern is a reversible reduction in bone mineral density with prolonged use, which is a specific consideration in adolescents and in those with other risk factors for osteoporosis.

Implant

The subdermal etonogestrel implant, inserted into the upper arm and lasting 3 years, is the single most effective reversible contraceptive method available, with a failure rate below 1 in 1,000 - it inhibits ovulation and removes the possibility of user error entirely once in place.³ The principal drawback is unpredictable bleeding (ranging from amenorrhoea to frequent or prolonged bleeding), which is the most common reason for early removal, and should be discussed explicitly before insertion so it does not come as a surprise.

Intrauterine methods

Copper intrauterine device (IUD)

The copper IUD is non-hormonal, working through a local inflammatory reaction toxic to sperm and ova, and lasts 5-10 years depending on the device. It tends to make periods heavier and more painful, which is an important counselling point, but has no hormonal side effects and can also be used as the most effective method of emergency contraception (see the Emergency Contraception article).

Levonorgestrel intrauterine system (IUS)

The IUS releases levonorgestrel locally, thickening cervical mucus and thinning the endometrium, and lasts 3-8 years depending on the specific device and indication. Unlike the copper IUD, it typically reduces menstrual bleeding substantially and is licensed for treating heavy menstrual bleeding as well as for contraception, and for endometrial protection as part of hormone replacement therapy.

Both intrauterine methods carry a small risk of uterine perforation at insertion and a small increased risk of pelvic infection in the first 20 days after insertion, related to introducing organisms already present in the lower genital tract at the time of fitting rather than the device itself. Expulsion occurs in a small minority, most often in the first 3 months.

Barrier methods

Male and female condoms are the only contraceptive methods that also reduce transmission of STIs, including HIV, which is why condom use is recommended alongside another method for people not in a mutually monogamous relationship, regardless of what other contraception is in use.¹ Diaphragms and caps, used with spermicide, are less effective and less commonly used than in the past, largely superseded by LARC methods.

Sterilisation

Vasectomy (division or occlusion of the vas deferens) and tubal occlusion (laparoscopic clipping or division of the fallopian tubes) are permanent methods, considered irreversible for the purposes of counselling even though reversal is occasionally technically possible with reduced success rates. Vasectomy is simpler, safer, and has a lower failure rate than female sterilisation, and semen analysis is required afterwards to confirm azoospermia before relying on it as the sole method.¹

Counselling before sterilisation should explore certainty about not wanting future children, alternatives (particularly LARC, which offers comparable effectiveness without permanence), and the small but real failure rate of both procedures.

Fertility awareness and lactational amenorrhoea

Fertility awareness methods track the fertile window using a combination of basal body temperature, cervical mucus changes and cycle-length calculations, avoiding intercourse during the fertile period; effectiveness depends heavily on training and consistency. The lactational amenorrhoea method can be up to 98% effective as a temporary method in the first 6 months post-partum, but only when breastfeeding is fully or nearly fully exclusive, the woman remains amenorrhoeic, and the baby is under 6 months old - all three conditions must be met.

Special situations

Post-partum contraception

The progestogen-only pill, implant and progestogen-only injectable can be started immediately after delivery, regardless of breastfeeding status. Combined hormonal methods should be avoided until at least 6 weeks post-partum in breastfeeding women (UKMEC 4 before 6 weeks) because of the VTE risk in the immediate post-partum period, and are UKMEC 2 in non-breastfeeding women after 3 weeks. Intrauterine methods can be fitted within 48 hours of delivery or delayed until after 4 weeks; insertion between these times carries a higher expulsion risk.

Perimenopause

Contraception is still required until 12 months after the last menstrual period in women over 50, or 24 months in women under 50, since ovulation can still occur despite irregular cycles. The IUS is a particularly useful option in this group as it can double as endometrial protection if HRT is later started.

Red flags

Prognosis and follow-up

Fertility returns promptly after stopping most methods, with the notable exception of the injectable, after which ovulation can take several months longer to resume than with other methods - a point worth discussing with anyone planning a pregnancy soon after stopping contraception. Routine follow-up after starting a new method (typically at 3 months for hormonal methods) allows blood pressure review where relevant, assessment of side effects, and an opportunity to switch method if the first choice is not well tolerated.