For the first time ever, the FDA has approved an app as an effective form of birth control.

After receiving the green light from the European Union last year, the app, called Natural Cycles, made its way overseas to the U.S. Now, it’s made history as America’s first form of government-approved digital contraception.

This is thrilling news to women who are searching for non-hormonal birth control options. However, it’s also stirred up controversy among some medical professionals, who insist using iPhones to prevent pregnancy is a method that’s doomed to fail.

Natural Cycles uses a specially-developed algorithm and a woman’s body temperature to determine which days she’s most fertile. On days with a high risk of pregnancy, a red light indicates: either don’t bone, or be sure to use protection. On days with a low risk, a green light signifies: you can bump uglies unprotected all day.

Natural Cycles claims to be just as effective as the pill at preventing pregnancy. In fact, by some measures, the app is actually more effective than the pill.

Clinical studies of Natural Cycles' effectiveness found that when used perfectly, only 1.8 percent of users became pregnant, according to the FDA. With “typical use” of the app (because no one’s perfect) 6.5 percent became pregnant.

By comparison, birth control pills fail 9 percent of the time, condoms fail 18 percent of the time, and IUDs fail less than 1 percent of the time, according to the Centers for Disease Control and Prevention.

Plenty of cycle-tracking apps came before Natural Cycles. But most of them fail at their fundamental job of finding the right fertility window.

Before Natural Cycles came along, “fertility awareness” was one of the least effective birth control methods with a 24 percent failure rate, worse than even the pull-out method.

Doctors are concerned that the new FDA-approved app won’t be much of an improvement on traditionl "fertility awareness" methods because it relies on users to follow an exact routine. Women have to take their temperature at the exact same time every morning, and minor changes like going to the bathroom first or having a sip of coffee can entirely throw off the accuracy of the thermometer.

Natural Cycles currently has more than 900,000 users, and aims to give even more women more choice when it comes to contraception. And that's exactly what it does —compared to rubbers, pills, or the pull-and-pray method, an app is an attractive alternative.