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Plan B and other Morning-After / Emergency Contraception pills

Plan B is a pill to be taken within 72 hours following intercourse to prevent a pregnancy. The earlier you take it, the more effective it is. All material we researched suggest it should not be used as regular contraception. In 2008, Canada became the 5th country in the world to approve Plan B over-the-counter (Eggertson, 2008). 

How the Pill works

Plan B's (2021) website states that it works in three ways: temporarily stopping the release of an egg from an ovary, preventing fertilization and/or preventing a fertilized egg from implanting to the uterus wall. Health Link BC (2021) website explains that emergency contraception such as Plan B "make the fallopian tubes less likely to move an egg toward the uterus. Emergency contraception is also thought to thin the lining of the uterus, or endometrium. The thickened endometrium is where a fertilized egg would normally implant and grow." So if there is a fertilized egg it cannot implant on the uterine wall. The pill uses a hormone called levonorgestrel. This same hormone is used in other birth control pills, but at a higher dosage (Plan B, 2021).

Campbell, Busby, and Steyer (2008) conducted a survey with women visiting a family physician on their views on emergency contraception. They found "that the majority of women surveyed did not know that one possible mechanism of action of Emergency Contraception (such as Plan B) is to prevent implantation of a fertilized ovum." Informed consent is important before taking any medication. "This study raises questions regarding women’s understanding of Emergency Contraception and demonstrates the need to better educate them about its possible mechanisms of action."

Plan B Effectiveness - and Ineffectiveness

Effectiveness for the Plan B pill is determined by the ability to stop an egg from being fertilized, or preventing a fertilized egg to implant in the uterus. The Canadian Medical Association states that "pills containing levonorgestrel may not prevent pregnancy in women who weigh 165 pounds or more" and "In Canada, the emergency contraceptive formulation of levonorgestrel is sold as Plan B and its labelling [leaves out the fact] that efficacy is related to body weight." 


Side Effects

Planned Parenthood's (2021) website states that Plan B "is super safe, and Plan B side effects aren’t super common. There have been no reports of serious problems out of the millions of people who’ve taken it." 

Concerns or Cautions with the pill

Plan B's (2021) website says, "If you already have a confirmed pregnancy, you should not use Plan B® because it will not be effective" (the website defines pregnancy as "a fertilized egg has attached to the wall of the uterus"), Plan B® does not work if you are already pregnant." P.J. Riga (2014) suggests that if life is understood to begin at conception, Plan B may be understood to be an "abortifacient" (making it "possible that its use will terminate an actual human life") as there is the potential for the pill to eliminate a fertilized egg that has not yet implanted in the uterus. This is important to know for those who have such convictions.


Campbell, J.W., Busby S.C., and Steyer, T.E. (2008). Attitudes and beliefs about emergency contraception among patients at academic family medicine clinics. Annals of Family Medicine, 6(1), 523-S27. Retrieved from:
Eggertson, L. (2014). Plan B emergency contraceptive may be ineffective for heavier women. Canadian Medical Association Journal, 186(1), E21-E22. Retrieved from:
Eggertson, L. (2008). Plan B comes out from behind the counter. Canadian Medical Association Journal,
178(13), 1645-1646. Retrieved from: 

Health Link BC. (2021). Emergency contraception. Retrieved from:
Plan B. (2021). How it works and FAQ. Retrieved from:

Planned Parenthood. (2021). What's the Plan B morning after pill? Retrieved from:
Riga, P.J. (2014). Plan B morning after pill. The Linacre Quarterly, 81(2), 101-102. Retrieved from:

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