01Purpose and principlesWhat the treatment does and how it fits into care.
Progestogen-only pills prevent pregnancy mainly by thickening cervical mucus; desogestrel and drospirenone also suppress ovulation more consistently than traditional preparations. This pharmacological difference creates distinct missed-use windows. A prescription written simply as “mini-pill” is unsafe because the user cannot know whether the permitted delay is three, 12 or 24 hours.
Traditional and desogestrel POPs use active tablets continuously. Drospirenone uses 24 active tablets followed by four placebo tablets, so errors must be placed within its pack. Starting protection and the time needed after missed use also differ. Bleeding is unpredictable and does not reliably indicate either ovulation or pregnancy.
Eligibility and effectiveness are separate. POPs avoid oestrogen-related VTE restrictions, yet hepatic enzyme induction can lower progestogen exposure. The interaction continues for 28 days after the inducer stops. UPA is a progesterone-receptor modulator, so POP use in the preceding seven days or restarting within five days can reduce its ability to delay ovulation.
Key points
- Traditional levonorgestrel or norethisterone POP has a three-hour late window, desogestrel has a 12-hour window and drospirenone has a 24-hour window; missed use begins beyond 27, 36 and 48 hours since the previous pill respectively.
- Take the missed pill as soon as remembered and continue at the usual time, even if two are taken in one day; use backup for 48 hours with traditional or desogestrel POP and seven days with drospirenone POP.
- Assess EC after unprotected sex from the time the first pill was missed until efficacy is re-established. Recent progestogen can reduce UPA effect, so use the current EC algorithm.
- After LNG emergency contraception a POP can start immediately; after UPA wait five days, then use backup for another two days with traditional/desogestrel or seven days with drospirenone, and test 21 days after the latest unprotected sex.
- Enzyme-inducing medicines can reduce all POP efficacy during treatment and for 28 days afterwards; offer DMPA or intrauterine contraception if eligible rather than assuming a higher pill dose solves the interaction.
- Irregular, frequent, prolonged or absent bleeding is common. Exclude pregnancy, infection, cervical or endometrial pathology when the pattern, symptoms, age or risk factors require it.
- POPs do not contain oestrogen and can often be used when CHC is unsuitable, but current breast cancer and some severe diseases still require exact UKMEC assessment.
02Indications, selection and cautionsWho may benefit, who needs urgent treatment and important alternatives.
More than 27 hours since the previous levonorgestrel or norethisterone pill is missed use and triggers 48-hour backup.
More than 36 hours since the previous desogestrel pill exceeds its 12-hour allowance and needs 48-hour backup.
More than 48 hours since the previous active drospirenone pill exceeds its 24-hour window and requires seven-day backup.
Amenorrhoea or irregular bleeding can occur without loss of efficacy, but clinical context determines whether investigation is needed.
Pain, bleeding or collapse with a positive or possible pregnancy requires urgent pregnancy-location assessment despite low absolute risk.
03Assessment before treatmentTests and checks that guide safe selection.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Exact product and dosing historyFirst step - Why
- Determine the active ingredient, pack design and elapsed time since the last active tablet.
- Interpretation and limitations
- Brand colour and the term mini-pill are insufficient; classify against the traditional, desogestrel or drospirenone rule.
- 02
Pregnancy test with dated follow-up - Why
- Identify established pregnancy and detect conception after a recent missed-use interval.
- Interpretation and limitations
- A negative test before 21 days from the latest unprotected sex can be too early and needs repeat testing.
- 03
Medicine interaction review - Why
- Identify enzyme inducers, UPA exposure and potassium-raising medicines relevant to drospirenone.
- Interpretation and limitations
- Use start and stop dates because induction persists for 28 days and UPA needs a five-day hormone-free interval.
- 04
Bleeding assessment - Why
- Distinguish an expected method effect from pregnancy, infection or structural disease.
- Interpretation and limitations
- New pain, postcoital bleeding, anaemia, examination findings or age-related risk changes the threshold for investigation.
04Treatment approachPreparation, options, escalation and aftercare.
01Missed-pill pathwayName the pill before counting hoursFirst stepA POP user reports a pill later than the scheduled time.+
- 1Confirm traditional, desogestrel or drospirenone formulation and calculate hours since the previous active tablet.
- 2Apply the 27-, 36- or 48-hour threshold, take an active pill now and continue the pack.
- 3Use 48-hour or seven-day backup as appropriate, assess EC for recent sex and arrange a 21-day pregnancy test.
02Interaction pathwayProtect efficacy during enzyme inductionA POP user starts or stops carbamazepine, rifampicin, selected antiretrovirals or another inducer.+
- 1Confirm whether the medicine truly induces hepatic enzymes and establish the treatment dates.
- 2Offer DMPA, an LNG-IUD or copper IUD if eligible; if POP continues, explain reduced reliability and add condoms.
- 3Maintain the interaction plan throughout use and for 28 days after the inducer ends.
03Bleeding pathwayManage symptoms without promising regularityIrregular or absent bleeding is unacceptable or has changed after established use.+
- 1Check adherence, pregnancy risk, medicines, pain, discharge, postcoital bleeding and screening history.
- 2Investigate pregnancy, infection, cervical or uterine pathology when indicated rather than attributing every change to POP.
- 3Discuss continuation, formulation switch or another method according to preference and clinical findings.
05Regimens, contraindications and interactionsTreatment details and the circumstances that modify them.
Desogestrel 75 microgram POP
Take one active tablet orally at the same time every day without a hormone-free interval; a dose is late after 12 hours and missed after more than 36 hours since the prior pill.After missed use take a pill now, continue daily, use 48-hour backup and assess EC; enzyme inducers reduce effectiveness.
Drospirenone 4mg POP
Take one active tablet daily for 24 days followed by four placebo tablets; an active pill is late after 24 hours and missed beyond 48 hours since the previous active pill.Use seven days of backup after relevant missed active pills; review renal, hepatic or adrenal disease and potassium-raising interactions.
06Complications, monitoring and follow-upAdverse effects, response and longer-term review.
- Review bleeding acceptability, adherence, pregnancy symptoms and new medicines rather than using routine examinations without indication.
- Recheck interaction dates and preserve alternative cover for 28 days after an enzyme inducer stops.
- After UPA, document the five-day delay before restarting and the formulation-specific backup interval.
- Use a pregnancy test 21 days after the latest unprotected sex whenever recent risk cannot be excluded.
07Special situationsVariants, exceptions and circumstances that change the usual approach.
Three pills mean three clocks
Traditional, desogestrel and drospirenone products differ in ovulation suppression, late windows and time to re-establish efficacy.
Bleeding is not a test
Amenorrhoea does not prove pregnancy protection and irregular bleeding does not prove contraceptive failure.
UPA and progestogen compete
Recent or rapidly restarted progestogen can reduce ulipristal’s ovulation-delaying action.
Interaction persists after stopping
Enzyme activity can remain clinically relevant for 28 days after the inducing medicine ends.
08Common pitfallsFrequent interpretation and management errors.
- 01
Giving every POP user a three-hour missed-pill rule.
- 02
Restarting hormonal contraception immediately after ulipristal.
- 03
Assuming oestrogen-free means no medical eligibility assessment.
- 04
Ignoring enzyme induction or treating antibiotics as a single interaction class.
- 05
Reassuring about pelvic pain solely because pregnancy is uncommon.