F.D.A. guidelines take a snapshot in time. Clinical research is continuing. Best practices are constantly improving. The F.D.A. can’t keep up, and when a drug maker wants the agency to update its guidelines, it must submit a complex and costly application. Fortunately, there’s a legal shortcut: Physicians can and often do prescribe medications off-label — i.e., for uses or in regimens different from what the F.D.A. recommends. A 2006 study estimates that 21 percent of all prescriptions are for off-label use.

Medication abortion is extremely safe, with less than a third of 1 percent of cases resulting in a serious adverse event. By 2011, when Ohio enacted its law, physicians had amassed a large body of research on ways to dose, time and administer the drugs used in a medication abortion that were more effective than the F.D.A. guidelines. A vast majority of health care providers in Ohio, and the rest of the country, were routinely using an updated treatment regimen that was based on the latest scientific published literature but had not yet been approved by the F.D.A. This regimen was recommended by the American College of Obstetricians and Gynecologists and the World Health Organization. But the guidelines stayed the way they were because there was little incentive for the small company that distributes mifepristone, the first medication used in a medication abortion, to submit an application to update them.

Not only is the law misguided; it also led to worse outcomes for women’s health. We examined medical charts from almost 3,000 patients at four Ohio clinics getting medication abortions before and after the law. After the law, the percentage of patients requiring additional medical treatment rose from 5 percent to 14 percent — including, in some cases, an in-clinic procedure to complete the abortion, which is what many women were trying to avoid by opting for a medication abortion in the first place.

The four clinics we studied saw an 80 percent decline in medication abortions between 2010 and 2014, compared with a 17 percent decline in all abortions over the same time period. Medication abortions declined from 22 percent of all abortions in these clinics in 2010, before the law, to 5 percent after the law in 2014.

There is some good news at the federal level: The F.D.A. label for medication abortion was updated in March 2016 to match the latest guidelines, so providers in Ohio — as well as in North Dakota and Texas, which have similar laws — may now legally treat women with the current evidence-based regimens.