Progestogen-Only and Long-Acting Contraception
The combined pill is elegant, but it carries a passenger the body doesn't always tolerate: oestrogen, and with it the shadow of clots. For the woman who smokes past 35, the migraineur who sees aura, the mother nursing a newborn, oestrogen is off the table. What remains is a whole quieter family of methods — progestogen alone in a pill, an implant, an injection, a coil — and one non-hormonal outlier that works by nothing more than copper. The best of them ask almost nothing of the user, and that, more than any laboratory number, is why they so rarely fail.
A 37-year-old woman comes to clinic for contraception. She smokes ten cigarettes a day and gets migraines that begin with flickering zig-zags in her vision. On the combined pill's own terms she is a textbook exclusion: smoking over 35 and migraine with aura each, on their own, push the added VTE and stroke risk of oestrogen beyond what is acceptable. She is disappointed — she liked the predictable bleeding the combined pill once gave her friend. But the conversation is not over; it has barely started. Oestrogen is what is contraindicated, not contraception. There is a progestogen-only pill she could take today, an implant that would last three years, an injection every twelve weeks, a hormonal coil that would also lighten her periods, and a copper coil with no hormones at all. Her problem is not "no options." It is choosing among five good ones.
When oestrogen is the problem
Half of contraceptive prescribing is really a question about oestrogen. The combined hormonal methods — covered in full in the Combined contraception chapter — owe their main serious risk to the oestrogen component: a raised chance of venous thromboembolism (VTE) and, in the wrong patient, arterial events like stroke and myocardial infarction. The UK Medical Eligibility Criteria (UKMEC) therefore rule oestrogen out in a recognisable set of people: a history of VTE or thrombophilia, migraine with aura, smokers aged 35 or over, uncontrolled hypertension, and the breastfeeding mother in the early postpartum weeks. For all of these, the progestogen-only and long-acting methods are not second best — they are the correct first choice, precisely because they carry the contraceptive benefit without the oestrogen risk. Progestogen alone has a far lower VTE and arterial risk than any combined method, which is what makes this whole family safe where oestrogen is not.
The progestogen-only pill (POP)
The progestogen-only pill delivers no oestrogen at all, so it is available to almost everyone the combined pill excludes. It works on three fronts. First and most reliably, it thickens the cervical mucus into a plug that sperm struggle to cross. Second, it thins the endometrium, making it inhospitable to implantation. Third — and this depends on the drug — it can suppress ovulation. The older progestogens (like levonorgestrel and norethisterone) act mainly on mucus and endometrium and only inconsistently block ovulation, so they demand strict timing: taken more than about three hours late, the mucus effect wanes and cover is lost. The newer desogestrel POP is different: it reliably inhibits ovulation as well, which both raises efficacy and buys a far more forgiving 12-hour missed-pill window. The underlying progestogen pharmacology — receptor actions, the individual molecules — belongs to the Endocrine section; here we care about how those actions are harnessed for contraception.
The characteristic downside is bleeding. Because the POP thins the endometrium without the cyclical oestrogen that builds and sheds a tidy lining, bleeding becomes unpredictable: some women stop bleeding altogether, many bleed irregularly, a few bleed frequently. None of this is dangerous, but it is the single commonest reason women abandon the method, so it must be discussed honestly before starting. Other progestogenic effects — acne, breast tenderness, mood changes, and reduced libido in some — are usually mild and often settle. What the POP does not carry is the oestrogen-driven VTE and stroke risk, which is the whole point.
- The POP contains no oestrogen, so it suits smokers >35, migraine with aura, VTE history and breastfeeding.
- Mechanism: thickens cervical mucus, thins endometrium; desogestrel also inhibits ovulation.
- Traditional POPs need strict ~3-hour timing; desogestrel gives a forgiving 12-hour window.
- Irregular bleeding is the main downside and the commonest reason for discontinuation.
- Progestogen-only VTE/arterial risk is far lower than any combined method.
LARC: fit it and forget it
The most effective methods are the ones that don't depend on remembering. Long-acting reversible contraception (LARC) is the umbrella term for methods that, once in place, keep working for years with no daily action from the user. That user-independence is not a convenience footnote — it is the reason they are the most effective reversible contraceptives that exist. There are four: the progestogen implant, the progestogen injectable, the levonorgestrel intrauterine system (IUS), and the copper intrauterine device (IUD). Three are hormonal (progestogen); one, the copper coil, uses no hormones at all. All are fully and promptly reversible on removal — with one important exception in the timing, which we will come to.
Think of the daily pill as a bucket you must top up by hand every single day: miss a few refills and it runs dry. LARC is a mains water supply plumbed into the wall — connected once, it simply keeps flowing, and no forgotten refill can ever empty it. That is why efficacy hierarchies put LARC at the top: the pill's real-world failure rate is dominated not by the chemistry but by the human being expected to remember it every day. Remove the human from the loop and the failure rate collapses.
The implant and the injectable
The progestogen implant is a single flexible rod, about the size of a matchstick, inserted under the skin of the upper arm. It slowly releases etonogestrel for around three years, and its dominant mechanism is different from the traditional POP: it primarily inhibits ovulation, backed up by the usual mucus and endometrial effects. It is, on the numbers, the single most effective contraceptive available — failure is exceedingly rare — precisely because nothing about it depends on the user once it is in. Its main nuisance, again, is unpredictable bleeding.
The progestogen injectable is depot medroxyprogesterone acetate (DMPA), given as an injection every twelve weeks. Like the implant, it works chiefly by inhibiting ovulation. It carries two cautions worth memorising because they set it apart from every other method. First, return of fertility is delayed — it can take up to a year after the last injection for ovulation to resume, so it is a poor choice for a woman planning pregnancy soon. Second, long-term use is associated with a reversible reduction in bone mineral density, mediated by the relative hypo-oestrogenic state it produces. Bone density largely recovers after stopping, but this makes DMPA a considered choice — not automatic — in adolescents, who are still accruing peak bone mass. The Endocrine section covers the oestrogen–bone axis that underlies this effect.
Two of the three progestogen LARCs — the implant and DMPA — are true anovulants: their main job is to stop ovulation. The hormonal coil is the odd one out. Sitting inside the uterus, it releases levonorgestrel almost entirely locally, so its dominant actions are on the endometrium and cervical mucus, and most women keep ovulating. That local action is exactly why the IUS has a second job no pill can match: it profoundly thins the lining and so dramatically reduces menstrual blood loss — which is why it appears again in the Menstrual disorders chapter as a first-line treatment for heavy menstrual bleeding, contraception and therapy in one device.
The two coils: hormonal and copper
The levonorgestrel intrauterine system (IUS) is a small T-shaped device placed in the uterine cavity, releasing levonorgestrel locally for around five to eight years depending on the product. Because the hormone acts where it is released, it thins the endometrium and thickens cervical mucus with only modest systemic effect. Bleeding typically becomes very light or stops altogether — a benefit for many, and the basis of its use in heavy menstrual bleeding. The copper intrauterine device (IUD) is the outlier of the whole chapter: it contains no hormone at all. The copper ions it releases are directly toxic to sperm and ova, impairing their motility and viability, and they set up a local inflammatory reaction in the endometrium that prevents fertilisation and implantation. Its trade-off is the mirror image of the IUS: periods often become heavier and more painful rather than lighter.
The copper IUD has one more distinction: it is the most effective form of emergency contraception. Inserted within five days of unprotected intercourse, its copper prevents fertilisation and implantation and fails far less often than any emergency pill — a role explored in the Emergency contraception chapter. So the same little device serves as both the best ongoing non-hormonal contraceptive and the best morning-after option, which is worth holding in mind when a patient presents late and asks for both.
POP: desogestrel (12-hour window) or traditional levonorgestrel/norethisterone (3-hour window). Implant: etonogestrel rod, ~3 years, mainly stops ovulation — most effective of all. Injectable: DMPA every ~12 weeks, stops ovulation, delayed fertility return + reversible bone density loss. Hormonal coil: levonorgestrel IUS, ~5–8 years, local action, lightens or stops periods (also treats heavy bleeding). Copper coil: copper IUD, up to ~10 years, no hormones, may make periods heavier, and doubles as the most effective emergency contraception.
- LARC (implant, DMPA, IUS, IUD) is the most effective category — user-independent once fitted.
- Implant (etonogestrel, ~3y) and DMPA (~12-weekly) work mainly by inhibiting ovulation.
- DMPA's two cautions: delayed return of fertility and reversible reduced bone mineral density.
- The levonorgestrel IUS acts locally, thins the endometrium and also treats heavy menstrual bleeding.
- The copper IUD is non-hormonal (copper toxic to sperm/ova) and the most effective emergency contraception.
- The efficacy hierarchy: LARC > user-dependent pills, because forgetting is the real failure mode.
Matching the method to the patient
Choosing among these methods is a structured conversation, not a default. Start with the hard constraints: is oestrogen contraindicated? If so, this whole family is the field. Then weigh the priorities the patient brings. Does she want the most effective option and the least to remember? Point her toward LARC — implant or a coil. Is she planning pregnancy within the year? Steer away from DMPA with its delayed fertility return, toward the implant or an IUS that reverse promptly on removal. Does she have heavy, painful periods? The levonorgestrel IUS solves two problems at once. Does she want to avoid hormones entirely? The copper IUD is the answer, at the cost of heavier periods. Is daily adherence realistic and a coil unwelcome? A desogestrel POP is reasonable, with its forgiving window. And in every case, the bleeding pattern must be discussed up front, because unpredictable bleeding — not efficacy — is what most often ends a method early.
- Telling a woman with migraine-with-aura or a smoker over 35 she "can't use hormonal contraception" — oestrogen is out, but every progestogen-only method and LARC is open to her.
- Starting DMPA in a woman who wants to conceive soon — fertility can take up to a year to return after the injection, unlike the implant or IUS.
- Missing that traditional POPs have only a ~3-hour late window; treating them like the 12-hour desogestrel pill loses contraceptive cover.
A 38-year-old woman who smokes and has migraine with aura wants highly effective contraception and hopes to conceive within the next year. Which method best fits her needs?
- Progestogen-only and LARC methods carry no oestrogen, so they are first choice when oestrogen is contraindicated (VTE risk, migraine with aura, smokers >35, breastfeeding/postpartum).
- The POP thickens mucus and thins the endometrium (desogestrel also stops ovulation); irregular bleeding is its main drawback, and traditional POPs need strict 3-hour timing vs desogestrel's 12 hours.
- LARC is the most effective category: implant and DMPA stop ovulation (DMPA delays fertility + reversibly lowers bone density); the levonorgestrel IUS acts locally and also treats heavy bleeding; the copper IUD is non-hormonal and the best emergency contraceptive.
- Match the method to the patient: oestrogen contraindications, desire for prompt reversibility, bleeding preferences and realistic adherence — and always discuss the bleeding pattern up front.
- Rang & Dale's Pharmacology — The reproductive system: contraceptive agents.
- Katzung. Basic & Clinical Pharmacology — Gonadal hormones and inhibitors; hormonal contraception.
- British National Formulary (BNF) — Contraceptives: progestogen-only, parenteral, and intra-uterine.
- FSRH (Faculty of Sexual & Reproductive Healthcare) Clinical Guidance — Progestogen-only pills, implant, injectable, and intrauterine contraception.
- UK Medical Eligibility Criteria for Contraceptive Use (UKMEC).
- NICE guideline — Long-acting reversible contraception (LARC).
