A recent letter to the editor by Amy Jacobson, of Planned Parenthood, ( "Emergency birth control backed," Aug. 29)urged everyone to "link arms" with Planned Parenthood to encourage the use of the over-the-counter drug commonly referred to as the "morning after pill."

Nowhere in Jacobson's letter did she define or even name the "emergency contraception" drug about which she was writing. This oversight is misleading, because there are various chemicals commonly referred to as the "morning after pill" that are not all equal in their mechanisms of action.

In the United States, a chemical that ends a pregnancy before implantation is medically and legally considered a contraceptive, as opposed to an abortifacient. An abortifacient terminates a pregnancy after implantation.

Contrary to what Jacobson wrote, there is still debate about whether progestin-only (Plan-B) and combined estrogen-progestin (Yuzpe regimen) "emergency contraceptives" are in fact abortifacients.

Where there is no question is about the drug RU-486, unequivocally an abortifacient. RU-486 is commonly, though incorrectly, called the "morning after pill."

Aside from Jacobson's misleading use of the term, "morning after pill," why are she and Planned Parenthood trying to make a distinction between contraceptives and abortifacients at all? Planned Parenthood advocates the use of RU-486. Its Web site states: "Since its approval in France in 1988, mifepristone (RU-486) has proven to be a safe, effective and acceptable option for women seeking abortion during the first several weeks of pregnancy."

Jacobson referred to "misinformation about the safety and efficacy" of "the morning after pill" by those who oppose its use.

In a paper published in April by Princeton University, "Emergency contraception: a cost-effective approach to preventing unintended pregnancy," eight studies found the effectiveness of Plan B use at between 59 percent and 94 percent. Two studies cited on the Yuzpe regimen showed its effectiveness to be between 47 percent and 53 percent.

One other thing Jacobson did not discuss was the common side effects of Plan B. According to the manufacturer's Web site, they include nausea, vomiting, stomach pain, tiredness, diarrhea, dizziness, breast pain, headache and menstrual changes. These potential side effects, as well as the percentage of effectiveness, would make some question both the safety and the efficacy of the product.