Oral Contraceptives

History

In 1951, activist Margaret Sanger began to work with Dr. Gregory Pincus to develop a birth control pill. In less than a year, Pincus was able to demonstrate that progesterone inhibits ovulation in rabbits and rats, but he lacked the funding necessary to continue his research. Simultaneously, an orally effective form of [Page 761]synthetic progesterone was created by Carl Djerassi, a chemist working in Mexico City, and Frank Colton, the chief chemist at the pharmaceutical company G.D. Searle. In 1953, philanthropist Katharine McCormick agreed to provide Pincus with funding for further research. Pincus collaborated with Dr. John Rock for the first human trials in 1954 and submitted the formulation developed by G.D. Searle and Company, called Enovid, for FDA approval in 1956. The FDA approved Enovid for treatment of severe menstrual disorders the following year. Searle received FDA permission in 1960 to sell a lower dose formula of Enovid as a contraceptive. In 1962, the drug company Syntex released another oral contraceptive, Ortho Novum, using the formula developed by Djerassi. The progestin-only pill was developed in the early 1970s in response to concerns about the relationship between estrogen and thrombo-embolic disease. In the 1980s, multiphasic oral contraceptives were developed that contain varying levels of progestin and estrogen throughout the standard 21-day cycle. Emergency contraception, a high dose of an oral contraceptive used by women after intercourse to prevent unwanted pregnancy, became more accessible beginning in the mid-1990s. In 2006, the FDA approved one option, Plan B, for use without a prescription for women aged 18 and older. Current oral contraceptives typically contain less than 1/10 the amount of progestin and 1/4 of the estrogen as found in the early versions.

Mechanism of Action

The hormones in combined oral contraceptives suppress both follicular development and ovulation. They also alter cervical mucus to make it more hostile toward sperm in case ovulation does occur. Progestin-only pills work by reducing and thickening cervical mucus to prevent sperm from reaching an egg. This type also inhibits the thickening of the uterine lining, which prevents a fertilized egg from implantation in the uterus.

The exact mechanism of action with emergency contraceptives is uncertain and may depend on the time in a woman's cycle that they are used. If taken at the beginning of a cycle, they may prevent or delay ovulation. If ovulation has already occurred, they may interfere with fertilization or implantation. The effectiveness of emergency contraceptives decreases as the length of time after unprotected intercourse increases.

Benefits

The most significant benefit of oral contraceptives is the decreased risk of pregnancy and pregnancyrelated complications, including ectopic pregnancy. Among ‘perfect’ users who do not miss any pills, approximately 1 woman in 1,000 become pregnant during the first year of use. Typical users have a pregnancy rate of 60 to 80 per 1,000 women during the first year. A World Health Organization (WHO) study found no significant difference in effectiveness when comparing six brands of combined pills. Progestin-only pills have slightly lower effectiveness.

...