Editing Combined oral contraceptive pill (section)

==== Effectiveness ====
If used exactly as instructed, the estimated risk of getting pregnant is 0.3% which means that about 3 in 1000 women on combined oral contraceptive pills will become pregnant within one year.<ref name=":22">{{cite book |title=Selected practice recommendations for contraceptive use |publisher=World Health Organization | vauthors = ((World Health Organization)) |isbn=978-92-4-156540-0 |edition=Third |location=Geneva |pages=150 |oclc=985676200 |year=2016 |hdl=10665/252267 |hdl-access=free | author-link = World Health Organization }}</ref> However, typical use of combined oral contraceptive pills by users often consists of timing errors, forgotten pills, or unwanted side effects. With typical use, the estimated risk of getting pregnant is about 9% which means that about 9 in 100 women on combined oral contraceptive pills will become pregnant in one year.<ref name="pmid27467196" /> The perfect use failure rate is based on a review of pregnancy rates in clinical trials, and the typical use failure rate is based on a weighted average of estimates from the 1995 and 2002 US National Surveys of Family Growth (NSFG), corrected for underreporting of abortions.<ref>{{cite journal | vauthors = Trussell J | title = Understanding contraceptive failure | journal = Best Practice & Research. Clinical Obstetrics & Gynaecology | volume = 23 | issue = 2 | pages = 199–209 | date = April 2009 | pmid = 19223239 | pmc = 3638203 | doi = 10.1016/j.bpobgyn.2008.11.008 | series = Contraception and Sexual Health }}</ref><ref>{{cite journal | vauthors = Trussell J | title = Contraceptive failure in the United States | journal = Contraception | volume = 83 | issue = 5 | pages = 397–404 | date = May 2011 | pmid = 21477680 | pmc = 3638209 | doi = 10.1016/j.contraception.2011.01.021 }}</ref>

Several factors account for typical use effectiveness being lower than perfect use effectiveness:

# Mistakes on part of those providing instructions on how to use the method
# Mistakes on part of the user
# Conscious user non-compliance with instructions

For instance, someone using combined oral contraceptive pills might have received incorrect information by a health care provider about medication frequency, forgotten to take the pill one day or not gone to the pharmacy in time to renew a combined oral contraceptive pill prescription.

Combined oral contraceptive pills provide effective contraception from the very first pill if started within five days of the beginning of the [[menstrual cycle]] (within five days of the first day of [[menstruation]]). If started at any other time in the menstrual cycle, combined oral contraceptive pills provide effective contraception only after 7 consecutive days of use of active pills, so a backup method of contraception (e.g. [[condom]]s) must be used in the interim.<ref name="Speroff 20052">{{cite book|title=A Clinical Guide for Contraception| vauthors = Speroff L, Darney PD |publisher= Lippincott Williams & Wilkins|year=2005|isbn=978-0-7817-6488-9|edition=4th|location=Philadelphia|pages=21–138|chapter=Oral Contraception}}</ref><ref name="FFPRHC COC2">{{cite web|url=http://www.ffprhc.org.uk/admin/uploads/FirstPrescCombOralContJan06.pdf|title=Clinical Guidance: First Prescription of Combined Oral Contraception|author=FFPRHC|year=2007|archive-url=https://web.archive.org/web/20070704044305/http://www.ffprhc.org.uk/admin/uploads/FirstPrescCombOralContJan06.pdf|archive-date=4 July 2007|url-status=dead|access-date=26 June 2007|author-link=Royal College of Obstetricians and Gynaecologists}}</ref>

The effectiveness of combined oral contraceptive pills appears to be similar whether the active pills are taken continuously or if they are taken cyclically.<ref name="Continuous or extended cycle vs. cy">{{cite journal | vauthors = Edelman A, Micks E, Gallo MF, Jensen JT, Grimes DA | title = Continuous or extended cycle vs. cyclic use of combined hormonal contraceptives for contraception | journal = The Cochrane Database of Systematic Reviews | issue = 7 | pages = CD004695 | date = July 2014 | volume = 2014 | pmid = 25072731 | pmc = 6837850 | doi = 10.1002/14651858.CD004695.pub3 }}</ref> Contraceptive efficacy, however, could be impaired by numerous means. Factors that may contribute to a decrease in effectiveness:<ref name="Speroff 20052" />

# Missing more than one active pill in a packet,
# Delay in starting the next packet of active pills (i.e., extending the pill-free, inactive pill or placebo pill period beyond 7 days),
# [[Intestine|Intestinal]] [[malabsorption]] of active pills due to [[vomiting]] or [[diarrhea]],
# Drug-drug interactions among combined oral contraceptive pills and other medications of the user that decrease contraceptive estrogen and/or progestogen levels.<ref name="Speroff 20052" />

In any of these instances, a backup contraceptive method should be used until hormone active pills have been consistently taken for 7 consecutive days or drug-drug interactions or underlying illnesses have been discontinued or resolved.<ref name="Speroff 20052" /> According to the US [[Centers for Disease Control and Prevention]] (CDC) guidelines, a pill is considered "late" if a user takes the pill after the user's normal medication time, but no longer than 24 hours after this normal time. If 24 hours or more have passed since the time the user was supposed to take the pill, then the pill is considered "missed".<ref name=":22" /> CDC guidelines discuss potential next steps for users who missed their pill or took it late.<ref>{{cite journal | vauthors = Curtis KM, Jatlaoui TC, Tepper NK, Zapata LB, Horton LG, Jamieson DJ, Whiteman MK | title = U.S. Selected Practice Recommendations for Contraceptive Use, 2016 | journal = MMWR. Recommendations and Reports | volume = 65 | issue = 4 | pages = 1–66 | date = July 2016 | pmid = 27467319 | doi = 10.15585/mmwr.rr6504a1 | doi-access = free | title-link = doi }}</ref>