Abortifacient
An abortifacient is a substance that induces abortion.

# History
The ancient Greek colony of Cyrene at one time had an economy based almost entirely on the production and export of silphium, a powerful abortifacient in the parsley family. Silphium figured so prominently in the wealth of Cyrene that the plant appeared on the obverse and reverse of coins minted there. Silphium, which was native only to that part of Libya, was overharvested by the Greeks and was effectively driven to extinction. The standard theory, however, has been challenged by a whole spectrum of alternatives (from an extinction due to climate factors, to the so-coveted product being in fact a recipe made of a composite of herbs, attribution to a single species meant perhaps as a disinformation attempt).
As the Catholic Church gained control of European society, women who dispensed abortifacient herbs found themselves classified as witches and were often persecuted (see witch-hunt). 

# Present time

## Herbal abortifacients
Many herbs and plants sold "over the counter" today may act as abortifacients, including wild carrot, black cohosh, slippery elm, pennyroyal, nutmeg, mugwort, papaya, vervain, common rue, and tansy. Typically, the labeling will contraindicate use by pregnant women, but will not contain an explanation for this warning. There is no available data on the efficacy of these plants in humans. Some animal studies have found them to be effective. The use of herbs to induce abortion should be avoided due to the risk of serious side effects.
King's American Dispensatory of 1898 recommended a mixture of brewer's yeast and pennyroyal tea as "a safe and certain abortive".
An older 'remedy' popular in the 1970s (previous to Roe vs. Wade) for unwanted pregnancy is using Vitamin C. "A Woman's Book of Choices: Abortion, Menstrual Extraction, RU-486" by Rebecca Chalker and Carol Downer, says to take 6-10 grams of ascorbic acid (pure Vitamin C) a day for 5-10 days.

## Pharmaceutical abortifacients
Mifepristone, a progesterone receptor competitive antagonist, was first approved in 1988 under the trade name Mifegyne for medical termination of early pregnancy in conjunction with a prostaglandin analogue. Mifepristone, also known as RU-486, is marketed under the trade name Mifegyne in France and countries other than the U.S., and under the trade name Mifeprex in the U.S.
Misoprostol, a synthetic prostaglandin E1 (PGE1) analogue, was first approved in 1988 under the trade name Cytotec for reducing the risk of NSAID-induced gastric ulcers. Misoprostol is approved in France under the trade name GyMiso for use with mifepristone for medical abortion. Misoprostol is used off-label with mifepristone for medical abortion in the U.S.
Misoprostol alone is sometimes used for self-induced abortion in Latin American countries where legal abortion is not available, and by some immigrants from these countries in the United States who cannot afford a legal abortion.

# Pre-implantation labeling controversy
Some substances might prevent implantation and thus destroy the blastocyst, although their known primary effect is to prevent fertilization.  The existence of these post-fertilization mechanisms is debated.  There is controversy as to whether pregnancy begins at the moment of fertilization, or at the moment the blastocyst implants in the uterine lining. American federal law and British law mark the beginning of pregnancy at implantation; thus, even if post-fertilization mechanisms were proven, these substances would still be labeled as contraceptives, rather than abortifacients.
The following birth control methods have been proposed to sometimes prevent implantation of a blastocyst, although (except as noted) they primarily work by preventing fertilization:
- Hormonal contraceptives
- Intrauterine device (IUD)
- The lactational amenorrhea method may cause a luteal phase defect (LPD). LPD may interfere with the implantation of embryos.
- Fertility awareness methods  a philosophy professor has speculated that intercourse during the less-fertile times of the cycle might create embryos incapable of implanting (due to aged gametes at the time of fertilization).
- Some herbal contraceptives may work primarily by preventing implantation.