Women used to try every herb they could think of to produce abortions, and of course most didn't work. And to sum it up succinctly, pregnancies are best prevented long before conception is considered. If you have intercourse around the time of ovulation you will have about an 8% chance of conceiving, if you use the current morning after pills, you will have that chance reduced to about 1-2%. The reason they aren't completely effective is that the current medications work to prevent ovulation.
However, there may be a new pill on the way that will reduce that chance even further: in fact, it has been estimated to be about twice as effective as Plan B. It is called Ella One, and we have been watching the progress since last year. When used in the first 5 days after unprotected sex, it is anti-progesterone and can prevent ovulation. It likely has an anti-progesterone effect on the uterine lining as well that prevents implantation, although that has not been specifically studied or any data given to prove this.
The FDA has now heard data from Watson Pharm. that it is a very safe method, and we are expecting that this may finally bring this pill to the US, although likely with a prescription to begin with. Although, some who liken a fertilized egg to an actual pregnancy will liken this technology to an actual abortion, making it a bit more controversial than just a contraceptive method.
Another aspect of this medication is in making it important that you have a gyno and a pharmacist that you are in tune with philosophically, as there are indications some may refuse prescriptions if they think it has abortifacient properties.