Women 18 and over now can purchase Plan B over the counter, says the FDA. Plan B is an oral contraceptive that is highly effective in preventing unwanted pregnancy if taken within 72 hours of unprotected sex.

Women 17 and younger will need a doctor's prescription to obtain the pills, although Plan B activists are continuing to press for minors to be allowed over-the-counter access.

Plan B, or levonorgestrel, is manufactured by Barr Pharmaceuticals. It is similar in makeup to regular birth-control pills but is more highly concentrated. A woman who takes Plan B within 72 hours of having unprotected sex can reduce the chance that she'll get pregnant by up to 89 percent. The earlier the pills are taken, the more effective they're likely to be.

Obviating the need for a doctor's visit and a prescription will make it possible for many women to take advantage of Plan B within the critical time frame to avoid an unplanned pregnancy.

Plan B is not the same as the so-called "abortion pill," which acts to terminate a pregnancy in its early stages. Should a woman already be pregnant when she takes Plan B, it would have no effect.

Getting approval for nonprescription sales of Plan B became a mission for some politicians. A group of US senators had threatened to withhold approval of Andrew von Eschenbach to head the FDA -- he's currently the Acting Commissioner of the Agency -- unless the Plan B controversy were settled. The brouhaha surrounding the issue likely spurred the resignation of his predecessor, Lester Crawford.

President Bush said at a press briefing on Wednesday that he supports the FDA decision.