A 19-year-old female starts Microgynon 30

A 19-year-old female starts Microgynon 30 (combined oral contraceptive pill) on day 8 of her cycle. How long will it take before it can be relied upon as a method of contraception?


2 days

5 days

7 days

Until first day of next period

Combined oral contraceptive pill: counselling

Women who are considering taking the combined oral contraceptive pill (COC) should be counselled in a number of areas:

Potential harms and benefits, including

  • the COC is > 99% effective if taken correctly
  • small risk of blood clots
  • very small risk of heart attacks and strokes
  • increased risk of breast cancer and cervical cancer

Advice on taking the pill, including

  • if the COC is started within the first 5 days of the cycle then there is no need for additional contraception. If it is started at any other point in the cycle then alternative contraception should be used (e.g. condoms) for the first 7 days
  • should be taken at the same time every day
  • the COCP is conventionally taken for 21 days then stopped for 7 days - similar uterine bleeding to menstruation. However, there was a major change following the 2019 guidelines. ‘Tailored’ regimes should now be discussed with women. This is because there is no medical benefit from having a withdrawal bleed. Options include never having a pill-free interval or ‘tricycling’ - taking three 21 day packs back-to-back before having a 4 or 7 day break
  • advice that intercourse during the pill-free period is only safe if the next pack is started on time

Discussion on situations where efficacy may be reduced*

  • if vomiting within 2 hours of taking COC pill
  • medication that induce diarrhoea or vomiting may reduce effectiveness of oral contraception (for example orlistat)
  • if taking liver enzyme-inducing drugs

Other information

  • discussion on STIs

*Concurrent antibiotic use

  • for many years doctors in the UK have advised that the concurrent use of antibiotics may interfere with the enterohepatic circulation of oestrogen and thus make the combined oral contraceptive pill ineffective - ‘extra-precautions’ were advised for the duration of antibiotic treatment and for 7 days afterwards
  • no such precautions are taken in the US or the majority of mainland Europe
  • in 2011 the Faculty of Sexual & Reproductive Healthcare produced new guidelines abandoning this approach. The latest edition of the BNF has been updated in line with this guidance
  • precautions should still be taken with enzyme inducing antibiotics such as rifampicin