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Everything You’ve Been Told About “Plan B” Is Wrong



Chris Kahlenborn, MD - published on 02/23/15

Chris Kahlenborn, MD explains how Plan B really works

Chris Kahlenborn, MD is the lead author of an article published this month in "Linacre Quarterly" — the journal of the Catholic Medical Association — on how the emergency "contraceptive" Plan B actually works. His findings will shock the many people who’ve been misled by advertising and other efforts to conceal the truth: When the risk of conception is greatest, Plan B (when taken before ovulation) is highly likely to cause an early abortion. But if taken on the day of ovulation or later, it not only fails to prevent clinical pregnancy, it may even increase the risk of pregnancy. Dr. Kahlenborn has prepared this helpful Q&A to explain how Plan B really works. Readers with additional questions are invited to contact him at

Does Plan B ever function as a contraceptive, i.e., by preventing sperm from fertilizing an egg?

Plan B should be called an emergency abortion/contraceptive instead of an emergency contraceptive, because it has a high potential to work as an abortifacient when given prior to ovulation. We noted in our recent paper (“Linacre Quarterly,” February 2015) that when given before ovulation, Plan B frequently allows ovulation to occur and it has no significant impact on sperm flow or quality. One would therefore expect an overall conception/pregnancy rate of 21 percent from unprotected intercourse during the fertile phase (the day of ovulation and the five preceding days). But if, following administration of Plan B prior to ovulation, one sees no evidence of clinical pregnancies, meaning that none of the newly-conceived embryos survived and successfully implanted, then an early abortion is the most likely mechanism of action. In a minority of cases — when there is a low risk of pregnancy from intercourse early in the fertile period and Plan B is taken promptly — it may actually stop ovulation and, therefore, work as a contraceptive.   

Plan B is supposed to "work" if taken within 72 hours of unprotected sex. But your paper says if Plan B is taken on the day of ovulation or later, it appears to have NO impact on pregnancy. So, would you say that Plan B is useless in preventing pregnancy if taken during or after ovulation?

Yes, it appears to be useless and may actually increase a woman’s risk of becoming pregnant when taken on or after the day of ovulation, according to the data presented by Gabriela Noé et al. in their 2010 and 2011 studies (“Contraception”). Other leading researchers — including those who support the use of Plan B, such as James Trussell and Frank Davidoff — have also raised this very real possibility:

“it even raises the counter-intuitive but undocumented possibility that Plan B used after ovulation might actually prevent the loss of at least some of the 40% of fertilized ova that ordinarily fail spontaneously to implant or to survive after implantation” (“JAMA,” October, 2006).

In practical terms this means that while Plan B likely often causes an early abortion when given prior to ovulation, when it is given on the day of ovulation or later, it is ineffective in preventing a clinical pregnancy and instead could actually enhance the likelihood of clinical pregnancy.   

Is it accurate to say that Plan B also appears to be useless in preventing clinical pregnancy among women whose body mass index (BMI) is over 30, i.e., moderately obese (for example a 5’4” tall woman who weighs 172 lbs.)?

It’s almost useless: Dr. Anna Glasier noted in 2011 (“Contraception”) that women with a BMI over 30 who take Plan B have a 400% higher failure rate than women of normal weight.

Are you saying the efficacy of Plan B is inflated, that the efficacy rate of 85 percent — claimed by the American Congress of Obstetricians and Gynecologists (ACOG) — is unsupported? and the Noé study estimate of 68 percent may also be too high?

According to the Noé paper, Plan B is almost 100% effective in stopping clinical pregnancy if given prior to ovulation and 0% effective when given on or after the day of ovulation. This means that the efficacy of Plan B depends on the composition of the particular study group. If the majority of women in the study sample are given Plan B preovulatory, efficacy will appear high; conversely, if the majority of women studied are given Plan B postovulatory, efficacy will appear low. We see evidence of this phenomenon in the Noé study: 103 women were in the preovulatory group and 45 in the postovulatory group. This corresponds almost exactly to their stated efficacy rate of 68% (i.e., 103/148 or 69.6%).

If I may summarize these findings: Plan B can prevent clinical pregnancy only if it is given to a woman before she ovulates and it does so mainly by causing an early abortion. What are the implications of these findings for emergency room physicians in their treatment of rape victims?

The Noé study has huge implications for women who have been raped and for the physicians who treat them. Department of Justice protocols recommend offering Plan B (or at least a prescription for Plan B) to all rape victims. And, according to its FDA-approved label, Plan B/Plan B One-Step is “indicated for prevention of pregnancy" and it “can be used at any time during the menstrual cycle” irrespective of whether the rape or “unprotected intercourse” occurred after ovulation and outside the fertile phase when the possibility of pregnancy is remote or nonexistent.

Patients are likely to be told that Plan B will reduce their risk of becoming pregnant. The reality is that most emergency rooms test for a prior existing pregnancy, but rarely if ever test women’s ovulatory status (by measuring levels of luteinizing hormone and progesterone). As noted earlier, top researchers who strongly advocate for Plan B have conceded that — in cases where women have begun to ovulate or have already ovulated — Plan B either has no effect or it may actually increase the risk of pregnancy. This has serious implications both ethically and medically. Emergency room physicians who continue to give Plan B without checking ovulation status, will subject many woman to a hormonal drug that may actually increase their risk of pregnancy, all the while claiming that Plan B has an efficacy rate of 85 percent!

What are the implications for Catholic hospitals that have been dispensing Plan B to rape victims on the assumption that it acts like a contraceptive when, in fact, your paper shows that when given during the fertile phase before ovulation, Plan B is more likely to prevent clinical pregnancy by an abortifacient, rather than contraceptive, mechanism of action?

In 1995, then Bishop John Myers accepted what is called today “the Peoria Protocol.” In a nutshell, the Peoria Protocol allows Plan B to be given to women who have been raped prior to ovulation only, based on the assumption that Plan B consistently stops ovulation when given in this phase. Many Bishops have accepted this protocol while others remained skeptical. We now know from several large studies by Noé et al., Croxatto et al. (Contraception, 2004) and others that Plan B does not consistently prevent ovulation. Therefore, the Peoria Protocol is based on a faulty premise.

This has immediate and serious implications for Catholic hospitals because giving Plan B prior to ovulation (following intercourse in the fertile phase) is more likely to cause an early abortion than to act as a contraceptive (by blocking ovulation or preventing fertilization). Catholic Hospitals currently using this faulty protocol are unwittingly allowing early abortions to occur in their facilities.  

What are the implications of redefining Plan B as effectively abortifacient (versus contraceptive) in battles over healthcare rights of conscience under the Obamacare mandate, concerns that have been raised by employers who do not want to provide coverage for "abortion-causing drugs" in their insurance policies? In other words, does your study strengthen the hand of all the “Hobby Lobby”s?

Plan B should be redefined as emergency abortion/contraception when given prior to ovulation because abortion appears to be its dominant method of action following intercourse, at least in the late fertile period. Informed consent dictates that women be informed of this method of action. Those who value human life in the earliest stages should not be coerced into giving or paying for this method of hormonal abortion.

Some who assert that Plan B works only as a contraceptive claim that it has little effect on the endometrium (the lining of the uterus) and, therefore, they conclude it could not cause an abortion. Is this true?

No. Proponents of Plan B often note that Plan B has not been shown to have an effect on the endometrium on a histological level. However, as we noted in our “Linacre” paper, when Plan B is taken prior to ovulation, it causes endometrial bleeding (menstruation) within 7 days about 30% of the time. This is gross anatomical evidence of an unstable endometrium. In addition, we noted that there is theoretical evidence that Plan B — like other progestins — may cause slowing of tubal transport of the embryo, which increases the risk of ectopic pregnancy (generally fatal for the embryo with or without emergency surgery) and can delay the timing and efficacy of implantation. While there are different ways in which Plan B may cause a living week-old embryo to be aborted, at this time, due to current technological constraints, it is difficult to determine the exact mechanism of action. However, as we noted in our “Linacre” article, in the future one will probably be able to quantify how frequently Plan B causes abortion by employing the use of sophisticated hormonal assays (for example, Early Pregnancy Factor) which can often detect the presence of pregnancy within 48 hours of fertilization.

Chris Kahlenborn, MD is a board-certified physician and the founder and director of The Polycarp Research Institute.

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