Plan B compared to withdrawal method

The British Medical Journal had a great editorial by Anna Glasier published earlier this month objecting to the false premise that Plan B will prevent abortions. Unfortunately, it's subscription only, but the excerpt is here. It's odd that the Brits are so interested in our Federal Food and Drug Administration.

More from that editorial:

Even if emergency contraception can work (is efficacious), the experimental evidence that it does work (is effective) is disappointing. Ten studies in different countries have shown that giving women a supply of emergency contraception to keep at home, so that they have it when they need it, increases use by twofold to threefold. In three studies that measured subsequent pregnancy rates, advance provision of emergency contraception increased its use but had no measurable effect on rates of pregnancy or abortion. When reasons for not using emergency contraception, despite having a supply at home, were documented three out of every four women said they did not realise they had put themselves at risk of pregnancy.

There's an equally great letter in response that's online, and free. The information about the emergency contraception, Preven being bought out and then removed by the manufacturers of Plan B is interesting, as is the statistic that shows that Plan B is no more likely to prevent pregnancy that the withdrawal method. Here's part of that letter:

Rapid Response

Re: Waking up to the morning-after pill

Ironically, within a couple of months the combined regimen, marketed as Preven, was voluntarily withdrawn from the U.S. market. Apparently, physicians did not appreciate that the combined regimen is twice as ineffective on an annual basis of perfect use when compared to the progestin-only regimen. With added irony, the withdrawal of Preven from the prescription use market received little attention, including from the American Medical Association, in stark contrast to the attention given to delays caused by the U.S. Food and Drug Administration concerning over-the-counter use of Plan B. The withdrawal was swept under the rug, and even the company website, www.preven.com, has now disappeared.

Yet what of the progestin-only regimen? In the United States, the prescription label for Plan B does not help us to answer this question. For, in an amazing sleight-of-hand, the label leaves doctors with nothing to compare it to! Specifically, the label presents annual use rates for traditional methods, but only the single use rate for perfect use of Plan B is included, not the annual use rate. To the unsuspecting, a single use rate of 89% may sound like a grand ("better than nothing") number. But little does one know that the relationship between single use and annual rates is exponential. For example, the 75% single use rate for Preven, when compared to the 89% rate for Plan B, implies a two-fold increase in annual rates (38 pregnancies per 100 women, versus 19). (3) So how could well-informed physicians have equated the two?

The plot thickens when we learn that the annual rate of pregnancy expectation for perfect use of Plan B, though available, was not included in the prescription label for comparison with traditional methods. It turns out that on an annual basis of pregnancy expectation, women can expect as many pregnancies from perfect use of Plan B (19 per 100 women in the first year of use) as they would from typical use of the withdrawal method! Notably, the same researcher, Princeton University professor James Trussell, had a hand in the publication of both of these statistics, and it was his work that the U.S. Food and Drug Administration had relied upon in making its decisions.

(emphasis is mine.)