Mangling, Mishandling, and Misrepresentation of Science in the Plan B Debate (Part II)

Read Part I of "Mangling, Mishandling, and Misrepresentation of Science in the Plan B Debate"

In all my searching, I have found no studies that support the notion that Plan B acts as an abortifacient. The only two proven methods of action are thickening of the cervical fluid and prevention of ovulation. The manufacturer of Plan B states that it may interefere with implantation, but I strongly suspect that they’re just covering their ass…ets.

From a 2005 Population Council press release:

"Over the past few years, reproductive physiologist Horacio B. Croxatto of the Chilean Institute for Reproductive Medicine in Santiago, Chile, and his colleagues have studied the effects of levonorgestrel [the active ingredient in Plan B] on the reproductive cycles of female rats, monkeys, and humans. Croxatto and one of his study partners, biomedical researcher Vivian Brache of PROFAMILIA in Santo Domingo, Dominican Republic, are members of the ICCR."

"Croxatto and his colleagues exposed female rats to very high doses of levonorgestrel at various stages of their reproductive cycles, either before or after ovulation or before or after mating. The researchers found that levonorgestrel inhibited ovulation totally or partially, depending on the timing of treatment and the dose administered. However, the drug had no effect on fertilization or implantation. This research was published in the May 2003 issue of the journal Contraception."

"Next, Croxatto and his colleagues studied the effects of levonorgestrel given to Cebus monkeys either before ovulation or postcoitally. The reproductive cycle of each animal was monitored by ultrasound examination of the ovaries, vaginal smears, and measurements of blood hormone levels, in order to time the administration of levonorgestrel. The researchers found that, when given before ovulation, levonorgestrel was able to inhibit or postpone ovulation. Alternatively, when it was given after mating—at a time when fertilization was believed to have occurred (on the basis of previous monitoring)—the pregnancy rates observed were identical in cycles treated with levonorgestrel or with a placebo. This indicates that levonorgestrel did not interfere with any postfertilization process required for embryo implantation. This research was published in the June 2004 issue of the journal Human Reproduction."

"[…]Croxatto, Brache, and their colleagues studied the effects of levonorgestrel administered during this fertile preovulatory period of women’s menstrual cycles. The researchers used Plan B®, a levonorgestrel-containing emergency contraceptive product marketed in the United States and Canada."

"Twenty-nine women in Santiago and 29 women in Santo Domingo were enrolled in the study. All of the women were protected from pregnancy by tubal ligation or a nonhormonal intrauterine device. The study was randomized, double-blind, and placebo-controlled. Women were treated with either a placebo, a full dose of Plan B emergency contraception, or a half dose of the drug. They were followed over several menstrual cycles and, by the end of the study, each woman had received all three of these treatments, separated by resting cycles. The women were randomly assigned to receive the treatments at specific times during the fertile preovulatory period, according to the diameter of the leading ovarian follicle, as determined by ultrasound. The leading ovarian follicle is the structure that ruptures to release the egg."

"In 82 percent of Plan B–treated cycles, follicles failed to rupture within the five-day period following treatment (the maximum time span sperm would survive in the female reproductive tract), or there was some significant abnormality in ovulation. These conditions occurred in only 41 percent of placebo cycles. The rate of failed or abnormal ovulation that was observed with Plan B treatment is identical with the estimated efficacy rate of Plan B emergency contraception. Blood tests on these women indicated that Plan B influences ovulation by suppressing the surge of luteinizing hormone (LH), the hormone that triggers ovulation."

"’There is no doubt that fertilization would not have taken place in those women should they have had intercourse prior to treatment,’ says Croxatto. ‘We conclude that the effects exerted by Plan B, when it is taken before the onset of the LH surge, may fully explain the pregnancies averted by emergency contraception. Failure to affect the LH surge, because treatment was begun too late in the fertile preovulatory period, explains the 20 percent failure rate of this method. Our data presented in this paper suggest that emergency contraception using levonorgestrel works by disrupting ovulation, not by interfering with implantation.’ This research was published in the December 2004 issue of the journal Contraception."

Can I say definitively that Plan B does not interfere with implantation? No. Do I believe that the evidence against it acting in that manner is sufficient to call the drug contraceptive rather than abortifacient? Yes. If someone can provide research that shows a link between Plan B and spontaneous abortion, I’ll be glad to look at it. In the meantime, I’m with this guy:

"’The post-fertilization effect was purely a speculation that became truth by repetition,’ says Joe DeCook, MD, a retired OB/GYN and vice president of the American Association of Pro-Life Obstetricians and Gynecologists. ‘In our group the feelings are split. We say it should be each doctor’s own decision, because there is no proof.’"

So, what have we learned today?

  1. Breastfeeding prevents pregnancy via increased levels of prolactin, not progesterone.
  2. Prolactin does not affect the endometrium, so it does not affect implantation.
  3. There is no evidence that Plan B affects implantation.
  4. There is evidence that suggests that Plan B only prevents conception by either making cervical mucus hostile to sperm or preventing ovulation.
  5. Being liberal or conservative does not make one immune to stupidity or ignorance.

Comments 11

  1. Beverly Nuckols, MD wrote:

    Thank you for covering this very timely subject. I am constantly amazed that neither side of the debate seems to want this information to be known.

    Posted 14 Jun 2006 at 6:34 pm
  2. Martin LaBar wrote:

    Thanks for doing this. I found these posts through the Christian Carnival.

    Posted 15 Jun 2006 at 6:05 am
  3. Linda Johnson wrote:

    There’s an excellent source of information and resources to help women with issues related to pregnancy and in particular, cervical mucus pregnancy at:

    Cervical Mucus Pregnancy

    Linda Johnson

    Posted 28 Jun 2006 at 4:45 am
  4. Purple_Kangaroo wrote:

    So am I understanding correctly that Plan B only works if the woman has not ovulated before she takes the pill? If it works only by preventing ovulation and inhibiting fertilization, it would have no effect at all in most cases.

    In other words, if you take plan B 72 hours after having unprotected intercourse, it will have no effect whatsoever except in the rare situation in which sperm have survived more than 72 hours AND ovulation has not taken place at any time in the few days before or the 3 days after having sex. Ovulation would have to take place after the 72 hours is over but before the sperm die for Plan B to be any more effective than no contraception at all.

    If that’s the case, then Plan B must be extremely ineffective at preventing pregnancy. I don’t see how the manufacturer’s claim that “treatment [with Plan B] initiated within 72 hours after unprotected intercourse reduces the risk of pregnancy by at least 75%” can possibly be true if it only acts to prevent ovulation and/or inhibit fertilization.

    Posted 26 Aug 2006 at 3:07 am
  5. Funky Dung wrote:

    Part of the problem is that ovulation is often predicted as 14 days after the start of menses – a terribly inaccurate approximation. Incorrect identification of ovulation could easily lead to incorrect an incorrect expectation of pregnancies and the prevention thereof.

    Posted 29 Aug 2006 at 1:31 pm
  6. Purple_Kangaroo wrote:

    Funky Dung, I don’t think incorrect identification of ovulation would affect something like the Plan B study.

    The only way the expected time of ovulation would even have an effect is if the researchers purposely (and successfully) made the study participants have intercourse 72 hours or more before ovulation happened, while at the same time somehow making the sperm survive more than 72 hours. That would be a really ineffective and dishonest way to prove the efficacy of a birth control method, since most women taking Plan B won’t be timing intercourse to take place exactly 72 hours or more before ovulation.

    To put it simply: For Plan B to work only in the way you are suggesting, the act of intercourse would always have to happen 72 hours or more before egg and sperm actually met. That is simply not going to be the case in that large a percentage. The group taking Plan B starting 72 hours after intercourse had a 75% lower rate of pregnancy than the control group. It seems nothing short of ridiculous to suggest that upwards of 75% of all pregnancies are not fertilized until 72 hours or more after the act of intercourse resulting in the pregnancy.

    The claim that Plan B does not inhibit implantation would require that fully 75% of the expected pregnancies were not fertilized until 72 hours or more after the act of intercourse. Sperm don’t usually live that long, for one thing, and an egg only lives for 24 hours after ovulation if unfertilized by that point.

    For a 75% success rate of birth control initiated 72 hours after intercourse, either Plan B would have to work by some method other than simply inhibiting ovulation/fertilization, or the statistics would seem to have been skewed or misrepresented somehow to make Plan B look more effective than it really is.

    Posted 31 Aug 2006 at 5:03 am
  7. Funky Dung wrote:

    This was a large study from the WHO involving women from 21 different countries. In this study, ovulation was determined by adding 14 days to the last period the subjects had. As anyone knows who have attempted to determine their own ovulation for fertility or for natural family planning, there is a wide variation in the moment of ovulation within a particular cycle. This is why change in temperature and changes in the quality of mucous are used in NFP to determine the naturally occurring fertility cycles. The method used by the women in the study cited is known to be quite inaccurate. For this reason, we would expect a significant portion of women who were placed in the post-ovulation group to actually be in the pre-ovulation or -ovulation group. In other words, there is ample reason to believe that the “reduction” of pregnancies from 10 to 2 in the “post-ovulatory” phase was the result of some of those women being in the pre-ovulatory or ovulatory phase of their cycle.

    Plan B EC: Does it Work if Taken After Ovulation?

    Posted 31 Aug 2006 at 8:53 am
  8. Purple_Kangaroo wrote:

    So it sounds like the the 75% rate may be only that 75% of pregnancies that would have been fertilized after 72 hours post-coitus are prevented by Plan B? That would make the “typical use” rate of efficacy would be far below 75%, wouldn’t it? I need to do a little research, I guess. The percentage of pregnancies that are fertilized later than 72 hours after coitus would be an important figure to know in calculating the true rate of efficacy.

    I’d sure like to see the entire text of some of these studies, rather than just the summaries. Do you know if they’re freely available online anywhere?

    Posted 31 Aug 2006 at 1:12 pm
  9. Beverly Nuckols, MD wrote:

    I have copies of the studies by Durand and Croxatto and can email them by pdf attachment to anyone who contacts me through my website email (b nuckols name at get rid of the space between initial and last name ).
    I’ve posted the most elegant and ethical study from Durand at (for educational purposes -’cause it needed to be done!) (But I feel guilty, anyway.)

    Posted 31 Aug 2006 at 6:01 pm
  10. Beverly Nuckols wrote:

    I’ve linked to this post in my “Review:Plan B” at

    Posted 02 Sep 2006 at 3:03 am
  11. Funky Dung wrote:

    The effectiveness of Plan B is reported to be somewhere between 90 and 75% in stopping an unintended pregnancy. If this is true, it seems impossible that it could work via a purely anti-ovulatory action. As Steve states here, the most important question to ask would be when did a woman ovulate. If Plan B is taken after a woman ovulates, and it contributes to the 75% effectiveness, then it must work at least part of the time via a post-fertilization event.

    If, on the other hand, Plan B works through predominantly anti-ovulatory actions, its effectiveness would be expected to be less than 75%. What does the data support? If one looks at some of the more recent studies, it is reasonable to conclude that the effectiveness of EC is significantly less than 75%.

    Plan B EC: What is its Real Effectiveness?

    Posted 06 Sep 2006 at 7:31 am

Trackbacks & Pingbacks 6

  1. From on 28 Sep 2006 at 7:48 am

    Ales Rarus comments on new notes at the LTI Blog citing evidence that Plan B is not very effective. As Serge summarizes on the LTI Blog, “As it was, the group who had to go to the pharmacy to get EC used it 197 times, while the group who had direct access used

  2. From JivinJehoshaphat on 11 Sep 2006 at 7:17 pm

    and over again I see no scientific studies provided to back up this assertion. Before declaring that Plan B prevents human embryos from implanting, we need to look at studies which have been done on Plan B to see if it actually prevents implants. Funky Dung did this back in June. There are a number of reasons to be opposed to selling a strong dose of a hormonal drug, whose long term side effects haven’t been studied, over-the-counter and I think Janice Shaw Crouse does a good job of outlining some of them

  3. From Ales Rarus - A Rare Bird, A Strange Duck, One Funky Blog » Mangling, Mishandling, and Misrepresentation of Science in the Plan B Debate (Part I) on 14 Jun 2006 at 2:04 pm

    […] Mangling, Mishandling, and Misrepresentation of Science in the Plan B Debate (Part II) […]

  4. From Plan B is Not Abortifacient | Science on 24 Aug 2006 at 9:46 am

    […] Plan B is Not Abortifacient By Funky Dung As any rregular reader of this blog is well aware, I’m strongly pro-life. However, I’m ticked off at my own movement right now because of crap like this [emphasis mine]:“President George Bush shocked the pro-life movement with his support for over-the-counter access to abortion-drug Plan B, also known as the morning-after pill, for adults. However, Plan B ‘ought to require a prescription for minors,’ he said.[…]“‘President Bush’s implied support of over-the-counter status for the abortion-causing drug Plan B is a betrayal of the pro-life principles he claims to support,’ said Stephen Peroutka, Esq., chairman of the National Pro-Life Action Center.”Let’s get with the program, people. Plan B is not abortifacient. Repeating “abortion” and “Plan B” in the same sentence over and over won’t make it so. As a devout Catholic, I’m no more a fan of Plan B than I am of condoms (or any other form of contraception), but since neither kill unborn children, there’s no just reason for banning them. Unless someone can provide evidence that Plan B causes abortions, I suggest we stop saying it does and move on to other matters. This is a poltical albatross. […]

  5. From RedBlueChristian » Blog Archive » Plan B is Not Abortifacient on 24 Aug 2006 at 9:50 am

    […] Let’s get with the program, people. Plan B is not abortifacient. Repeating “abortion” and “Plan B” in the same sentence over and over won’t make it so. As a devout Catholic, I’m no more a fan of Plan B than I am of condoms (or any other form of contraception), but since neither kill unborn children, there’s no just reason for banning them. Unless someone can provide evidence that Plan B causes abortions, I suggest we stop saying it does and move on to other matters. This is a political albatross. […]

  6. From Review: Plan B, How It Works and Doesn't Work (Vanity) on 18 Jul 2007 at 11:37 pm

    […] non physician who does a lot of research, "Ales Rarus" Mangling, Mishandling, and Misrepresentation of Science in the Plan B Debate (Part II)Another unquestionably pro-life blog, "Jivin’Jehosaphat" TOPICS: Culture/Society; […]

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