What about the FDA Information? [Serge]

Note: This is a post that I made over seven years ago.  A number of readers recently emailed me the same question.  I have updated the post with some new information and added a bit to the end.  The original post is here.

An e-mailer recently asked about the fact that the FDA does list prevention of implantation as a potential mechanism of action of Plan B. You can see that in the FDA certified package insert here. Does the FDA know something that we don't?

The FDA relies on information provided by the manufacturer for the mechanism of action of any medication (they do not do their own research).  In short, the manufacturer has a responsibility to list any possible mechanisms of action for any medications. Since there is an open question in the literature regarding the mechanism of Plan B, and since post-fertilization events are listed as one possible mechanism, it is not surprising (nor particularly helpful) that interruption of implantation is included as a possible mechanism of action.

In other words, the fact that the manufacturer mentions this as a possible mechanism is evidence that the question is an open one that we have no definitive answers to. Therefore, the presence of this information by the FDA does not trump the most recent literature on the topic. In fact, the opposite is true.

I can illustrate this in another way that does not directly address the mechanism of action of PlanB. The manufacturer makes this claim on the packaging of Plan B that the FDA agreed to:

How effective is Plan B® One-Step?
The sooner you take Plan B® One-Step, the better it will work. Take Plan B®
One-Step as soon as possible after unprotected sex. If it is taken as soon as
possible within 72 hours (3 days) after unprotected sex, it will significantly
decrease the chance that you will get pregnant. Seven out of every 8 women
who would have gotten pregnant will not become pregnant. 

I have noted in a number of posts beginning over 7 years ago that this claim is completely wrong.  There is no one aware of the research on Plan B who believes that it is over 87% effective.  In fact, recently we have discovered that for many, many women the effectiveness is essentially zero.  This is not new information - the FDA has very little incentive to stay current with the most recent research once a drug is on the market.

Here's the bottom line: the FDA is allowing the manufacturer of Plan B to claim that it can be almost 90% effective based very old data. These studies have been shown to be inaccurate due to its crude way of estimating ovulation.  Yet there it is on the packaging being readied for OTC sale.

Still confident in the FDA information now? There is significant reason why we should not be. In any event, it should be clear that the information given by the FTC does not refute more recent scientific studies.

Lastly, I wish to mention that the FDA really does not concern itself with mechanism of action.  Essentially, when a drug seeks FDA approval, it has to show that it is both safe and efficacious.  In other words, it does what it claims to do and doesn't do anything else too dangerous.  (As we can see, it sometimes fails in either one or both of these goals).  If a drug can show these two things, it is unimportant to indicate its mechanism of action.  In fact, for many drugs that we use, including the majority of the anesthetic drugs we use, we do not know the exact mechanism of action.