Oral contraceptives, or birth control pills, are reversible birth control method for women who wish to avoid pregnancy.

What is the birth control pill?

There are different kinds of birth control pills available in Canada. Combination pills use both estrogen and synthetic progesterone or progestin at different doses. The "mini-pill" contains only progestin. Progestin-only emergency contraceptive pills are available to prevent pregnancy after a contraceptive accident or when no form of birth control was used.

The first generation of combination pills came out in 1959 and contained very high doses of estrogen, which were associated with side effects such as weight gain and skin changes and, more worryingly, raised the risk of blood clots, heart attacks, and strokes, particularly in certain users. To counter these complications and to lower the rate of side effects, in the 1970s, the second generation of pills was developed with lower doses of estrogen and new types of progestin.

More recently, a third generation of pills containing even less estrogen and newer progestins has been developed with certain aims in mind: to decrease side effects such as acne and weight gain, to improve changes in cholesterol levels, and to decrease cardiovascular complications.

In addition to birth control pills, other hormonal methods are available including injection, contraceptive patch, contraceptive ring, and intrauterine system.

What does the birth control pill do?

In a combination pill, the estrogen and progestin combine for several contraceptive effects: inhibiting ovulation by affecting hormones, creating thick cervical mucus that slows the ability of sperm to fertilize an egg, making the uterus less hospitable to an implanted ovum, and other changes that prevent fertilization and implantation.

The "mini-pill" does not lead to as many changes and is consequently less effective than a combination pill, but when a woman can't take estrogen or doesn't want to take estrogen, the mini-pill is an acceptable alternative.

The emergency contraceptive pill works to prevent the release of the egg from the ovary, the uniting of the sperm and egg, and the attachment of the fertilized egg to the walls of the uterus.

The hormones in most pills also have varying degrees of "androgen" effect; that is, they convert in varying degrees to "male hormone," which accounts for some of the side effects the pill is noted for such as acne and increased appetite.

What to do when pills are missed?

A woman who has missed one or more pill should contact her pharmacist or doctor to find out the best plan to follow. The doctor may also advise using a backup method of birth control for at least a week.

Read "The pill: benefits" for more information.

Art Hister, MD 
in association with the MediResource Clinical Team