Beginning next month, a controversial single pill will become available over-the-counter for women 17 and older to prevent unintended pregnancies due to contraceptive failure or unprotected sex.

The single-dose pill replaces the two-pill emergency contraceptive known as the "Morning-After'' or Plan B-One-Step pill and will be available to women younger than 17 with a prescription. About seven out of eight women who would have gotten pregnant will not after taking the pill, according to officials at Plan-B, which is manufactured by Teva Pharmaceutical Industries.

Lifting the prescription requirement for women 17 and older means that patients no longer have to endure the sometimes long wait to see their doctors. The pill is most effective when taken within 72 hours of intercourse and even more so if taken within 24 hours.

Family planning experts, such as Ashlesha Patel at John H. Stroger Jr. Hospital of Cook County in Chicago, hailed the product as efficient, saying it allows patients to act quickly, while providing a high-level of safety and efficacy.

"It's supported by the family planning community here and abroad,'' said Dr. Patel, an obstetrician-gynecologist who is division director of family planning services at Stroger. On the other hand, conservative groups such as the Family Research Council have been critical of the pill, arguing that it could promote promiscuity among teens.

Almost half of the pregnancies in the U.S. are intended, according to the Centers for Disease Control and Prevention. A report from the Guttmacher Institute in New York also found that the rate of unintended pregnancies declined among adolescents, college graduates and the wealthiest women, but increased among poor and less educated women between 1994 and 2001, the most recent statistics available.

"The abortion rate and the proportion of unintended pregnancies ending in abortion among all women declined, while the unintended birth rate increased,'' the study says. "Forty-eight percent of unintended conceptions in 2001 occurred during a month when contraceptives were used, compared with 51 percent in 1994.''

Facts about the "Morning-After'' Pill:

• Plan B is not the abortion pill
• Plan B is not effective if a woman is already pregnant and will not terminate an existing pregnancy.
• Plan B is not a substitute for routine contraception and should not be used that way because it is not as effective.