• A woman who vomits (for any reason) within 2 hours of taking a progestogen-only pill (POP) should repeat the dose as soon as possible.
• If she is now more than 3 hours late (or 12 hours for desogestrel), continues to vomit or has very severe diarrhoea, the woman should follow the instructions for missed pills.
• If vomiting or severe diarrhoea persists for more than 24 hours, the woman should follow the instructions for missed pills, counting each day of vomiting and/or severe diarrhoea as a missed pill:
• Additional contraceptive cover is required during the illness and for 48 hours afterwards.

In depth

• Missed pill:
• Desogestrel (Cerazette^®): > 12 hours late (i.e. > 36 hours since taking the last pill).
• Other progestogen-only pills: > 3 hours late (i.e. > 27 hours since taking the last pill).
• If the woman has missed any progestogen-only pills, she should:
• Take a progestogen-only pill as soon as possible, then continue taking the pills as before. This can mean taking two pills within 24 hours.
• Use additional contraceptive protection for the next 48 hours.
• Consider whether emergency contraception is required. For more information, see the CKS topic on Contraception - emergency.

In depth

• Some drugs and herbal remedies may interfere with the effectiveness of progestogen-only pills (POPs).
• Women taking liver enzyme–inducing drugs should use additional contraception (e.g. condoms) whilst taking the drug and for 4 weeks after finishing the course:
• Commonly encountered liver enzyme–inducing drugs are:
• Antibiotics: rifampicin and rifabutin.
• Anticonvulsants: carbamazepine, oxcarbazepine, phenytoin, phenobarbital, primidone, topiramate.
• Herbal remedies: St John's wort.
• Antiretrovirals: drug interactions between certain antiretroviral agents and hormonal contraceptives could alter the safety and effectiveness of both the hormonal contraceptives and the antiretroviral agents. See antiretrovirals.
• Antibiotics that do not induce liver enzymes (i.e. all antibiotics except rifampicin and rifamycin) do not reduce the effectiveness of POPs.
• Emergency contraception should be considered if sexual intercourse has taken place in the past 5 days and the efficacy of the POP is doubtful — see the CKS topic on Contraception - emergency.

In depth

• Menstrual irregularities are common. Some women have frequent or prolonged bleeding, whilst some experience amenorrhoea.
• Identify and manage causes for bleeding irregularities such as missed pills, drug interactions, vomiting, severe diarrhoea, pregnancy.
• Exclude or manage other situations which could result in unscheduled bleeding, such as:
• Sexually transmitted infections.
• Risk of STI if the woman is under 25 years, or has a new sexual partner, or more than one partner in the last year.
• Pregnancy.
• Gynaecological conditions such as cervical cancer. Provided there is consistent and correct use of contraception, speculum examination is warranted:
• For persistent bleeding beyond the first 3 months of use.
• For new symptoms or a change in bleeding after at least 3 months of use.
• If the woman has not participated in a National Cervical Screening programme.
• If requested by the woman.
• After a failed trial of modification of POP treatment (at least 6–8 weeks).
• If there are other symptoms such as pain, dyspareunia, or post coital bleeding. (Note that these symptoms also warrant pelvic examination.)
• If frequent or prolonged bleeding occurs, consider the use of a different progestogen-only pill (POP).
• If the woman experiences amenorrhoea, exclude pregnancy. The POP can then be continued.

In depth