Throughout history, men and women have looked for safe, reliable, convenient ways to prevent pregnancy. Some have been based on medical knowledge, but many have arisen from superstition and old wives' tales. However, one category of contraceptives, those that use chemicals, have proved themselves valuable and trustworthy. Employed at least since ancient Egyptian and Greek times, chemical contraceptives are still the most successful and popular agents for birth control today.

Most modern chemical birth control methods are used by women and rely on synthetic versions of the hormones estrogen and progesterone. These simulate the biochemical effects of pregnancy. Thus, the user's body will not release an egg to be fertilized, since all signs indicate that a pregnancy is already under way. For this reason, the synthetic hormones are technically known as ovulation inhibitors.

Depending on the formulation, ovulation inhibitors can be as much as 99% effective at...