“Medical abortion represents a revolution in women’s reproductive health,” said Dana Hovig, the chief executive of Marie Stopes International, an aid group that provides women’s reproductive health services in 43 countries around the world. “It saves women’s lives and has enormous potential to increase access to safe abortion at minimal cost.”

Medical abortion causes a miscarriage that is indistinguishable from a natural one. That’s important for women in countries where they risk arrest if they seek help in a hospital after a botched abortion. The risks to a woman seem no greater than with a natural miscarriage, and there’s no known harm to a woman who turns out not to have been pregnant after all. One serious downside is that misoprostol is suspected of causing birth defects, perhaps 1 percent of the time, but only if it fails and the pregnancy continues to term.

In the United States, only about one abortion in eight is done with pills. Partly that’s because by law, mifepristone must be taken in a clinic. But worldwide, the number of medical abortions is surging, accounting for nearly 70 percent of all abortions in Scotland, according to Marie Stopes International.

It’s not clear how late in pregnancy medical abortion is feasible. “It sounds like a simple question, but it’s not,” Dr. Winikoff said. In some form and strength, medical abortion seems to work “from Day 1 to the end of pregnancy,” she said  but the effectiveness and safety of later-stage abortions still need to be worked out.

Image Misoprostol is an ulcer drug that also induces abortions.

In the United States, the pills can be taken up to nine weeks’ gestation. In Britain, inpatient use of the pills is permitted up to 24 weeks.

What do these pills mean for the political battles over abortion? To firm opponents of abortion, the means of ending a pregnancy doesn’t matter. But my hunch is that, for those in the middle, taking pills at home may seem a more natural process than a surgical abortion, and the result may be a tad more acceptance.