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" Question My sister became pregnant while taking the Pill.  How effective is the Pill in preventing pregnancy if instructions on the packet are adhered to?   Answer I&amp;#039;m sorry to hear about your sister&amp;#039;s predicament. You don&amp;#039;t say which Pill your sister was taking, as there are two types and their efficacy is different.  The commonest pill taken is the combined oral contraceptive pill, containing both oestrogen and a progesterone.  If this is taken properly the failure rate is very low &amp;amp;#8211; about 0.2 per cent per year.  The progestogen-only pill (POP) or mini-Pill has a higher failure rate of between 2 and 8 per cent per year.  Even if the instructions are strictly adhered to, there are other reasons why failure may occur.  If a pill is forgotten, it should be taken within 12 hours (three hours for the mini-Pill), but if the interval is longer than this then it is advisable to take other precautions such as a barrier method for the next seven days.  As you can see, timing is much more critical with the progestogen-only pill than with the combined pill.  Other reasons for failure include;   a stomach upset such as nausea and vomiting, when the Pill may not be properly absorbed into the system interaction with other drugs. Anti-epileptic drugs such as phenobarbitone and phenytoin and carbamazapine, griseofulvin (for fungal infections) and some broad spectrum antibiotics can all interfere with the efficacy of the combined contraceptive pill.  Yours sincerely The NetDoctor Medical Team   Other Qs &amp;amp; As Abnormal cells after a smear: can I still go the Pill? Acne and the pill Altering my menstrual cycle using the Pill Are extra precautions needed if two packs of Pills are taken one after the other? Blood disorder and the Pill Breakthrough bleeding while on the Pill Can I take my Pill without a seven day break? Changing Pills Concerned about breakthrough bleeding Confused about contraceptive pill Contraceptive pill Contraceptive pill and weight gain Delayed periods after stopping the Pill Diabetes and the Pill Does long-term use of the Pill affect fertility? Does metronidazole interfere with the progestogen-only pill? Does the Pill need to get into your system? For how long can I continuously use the Pill? Going on the Pill, aged 14 How should I time taking the Pill on holiday? How soon after starting the Pill is my partner protected? I can&amp;#039;t take the Pill Is it safe to start taking St John&amp;#039;s wort again? Is it safe to take the mini-Pill until the menopause? Is it safe to take the Pill without a seven-day break? Is the Pill to blame for my headaches, panic attacks and lack of libido? I&amp;#039;ve gained weight since starting the contraceptive pill Migraines and the combined pill Periods after the Pill Periods and the combined Pill Persistent problem with sore nipples Prescribing the Pill to under 16s Problems with Minulet Questions about the Pill Should I have a break from the Pill before starting a family? Side effects of the pill Skin discolouration caused by taking the Pill Stopping the Pill The Pill The Pill and antibiotics The Pill and monthly bleeds: are they necessary? Tips on taking the combined pill Travelling and the Pill What questions will the GP ask when I see him about the Pill? Will I gain weight by taking Dianette? Will the Pill make me put on weight? Would the Pill stabilise my hormones?   Last updated 18.03.2015 "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.netdoctor.co.uk/ask-the-expert/sexual-health/a3799/how-effective-is-the-pill/>