Girls 17 and younger still will need a doctor’s note to buy the pills, called Plan B, the Food and Drug Administration told manufacturer Barr Pharmaceuticals Inc. (BRL)

The compromise decision is a partial victory for women’s advocacy and medical groups that say eliminating sales restrictions could cut in half the nation’s 3 million annual unplanned pregnancies. Opponents have argued that wider access could increase promiscuity.

The pills are a concentrated dose of the same drug found in many regular birth-control pills. When a woman takes the pills within 72 hours of unprotected sex, she can lower the risk of pregnancy by up to 89 percent. If she already is pregnant, the pills have no effect.

The earlier it’s taken, the more effective Plan B is. But it can be hard to find a doctor to write a prescription in time, especially on weekends and holidays. Hence the push to allow nonprescription sales.

Barr has said it hopes to begin nonprescription sales of Plan B by the end of the year. The pills will be sold only from behind the counter at pharmacies – so the pharmacist can check photo identification – but not at convenience stores or gas stations.