Few scientific inventions have impacted society as fundamentally and powerfully as the contraceptive pill, or, as we have known it since it went on the market 40 years ago in Canada – The Pill.

It has been credited with launching the women's movement, fuelling the wild and free times of the 1960s, reforming the Roman Catholic Church. When Pope Paul VI issued an encyclical in the late-1960s condemning all forms of artificial birth control – most especially the Pill – many Catholics, priests included, responded with a groundswell stuff it!

The Roman Catholic Church sanctioned only the rhythm system as a method of birth control. After Pope Paul VI's encyclical, titled Humanae Vitae, prominent Canadian theologian Gregory Baum made stained-glass windows rattle around the Roman Catholic world when he said the Pill "does not interfere with the performance of the sexual act [and] its use is morally indistinguishable from the rhythm method."

In Canada, chemical birth control finally was legalized in 1969, the year after Pierre Elliott Trudeau became prime minister. Before that, doctors could only prescribe it to regulate the menstrual cycle (wink, nudge).

The Pill was the brainchild of Margaret Sanger, a lifelong champion of women's rights and birth control. She was born in 1879 in Corning, New York, the sixth of 11 children. Sanger – her married name – often blamed her mother's premature death on her frequent pregnancies. Sanger survived constant harassment, ridicule and even jail for popularizing various birth control methods.

In 1950, in her 80s, Sanger met Gregory Pincus, a reproductive scientist. Sanger raised $150,000 to get Pincus started on research that would lead to a successful universal contraceptive, The Pill, which became available in the United States in 1960.

It had been established in the 1930s that hormones could prevent ovulation in rabbits, but it was considered unethical to conduct such experiments on humans. Pincus was leery of using the hormone estrogen, knowing of the cancer risks. Instead he first developed a progestin-only contraceptive, which he tested on poor Puerto Ricans in the 1950s.

By the end of the 1950s, the Sanger/Pincus pill – Margaret Sanger died in 1956 – came onto the market under the brand name Enovid. It was welcomed by women as a marvel, but, as a New York Times report said last year, Enovid began its life as a "massive overdose."

After millions of woman had taken Enovid, and thousands died or became disabled by blood clots, it was discovered that the amount of hormones in Enovid was 10 times what was needed for contraception.

Women in their 30s and 40s today are the ones with mothers who were the first to take the Pill, with all its promises and risks. Does it cause breast cancer? Ovarian cancer? Blood clots? Infertility? Depression? Obesity? No worry, it turns out – despite the fact that the women 40 years ago regularly ingested birth control pills loaded with 300 micrograms of estrogen. Today, birth control pills rarely contain more than 50 mcg of estrogen, some as few as 20 mcg.

By the end of the millennium, the Canadian Contraception Study – published by The Journal of the Society of Obstetricians and Gynecologists – determined that 84 per cent of Canadian women use or have used the Pill.

A new, more radical approach is the concept that it may be healthier for women to remain on the Pill constantly, so as not to experience menstruation at all. This was explained in an article in The New Yorker last summer. It was also explained in an article by Stephanie Nolan in The Globe and Mail that quotes Sandra Byers, a psychologist and professor of human sexuality at the University of New Brunswick, who says, essentially, women do not have to bleed.

Dr. Elsimar Coutinho co-authored a book titled Is Menstruation Obsolete? "Recurrent menstruation is not natural, it's social," Coutinho says. "It's unnecessary, useless, and may be harmful."

The Pill has always been regarded as a method of easing painful menstruation, including cramps and nausea. By reducing menstrual flow, it lowers the risk of anemia, improves the skin and increases bone density, thus reducing the risk of osteoporosis.

The most recent commercially satisfactory development in the saga of the Pill is the "morning-after" pill. It became legal in British Columbia last December for a woman to visit a pharmacy and buy a "morning-after" contraceptive pill. This prevents a pregnancy if taken 72 hours after sexual intercourse, and can be used if a woman suspects failure of routine birth control, or if she had unprotected sex. No doctor's prescription is needed for the "morning-after" pill.

We've come a long way.

The Chemistry of Contraception

"The Pill" is the common name for oral contraception.

There are two types of oral contraceptives: combination pills (containing estrogen and progestin) and progestin-only pills. Estrogen and progestin are hormones made in the ovaries.

Both pills are intended to prevent pregnancy, but they work in different ways:

Combination pills prevent a woman's ovaries from releasing eggs. (ovulation)
Progestin pills can also prevent ovulation, but they usually work by thickening cervical mucus. This prevents sperm from joining with an egg.

Combination pills also thicken cervical mucus, and both types of pill may also prevent fertilized eggs from implanting in the uterus (womb).

Effectiveness

Combination pills are somewhat more effective than progestin-only pills. Less than one per cent of women who use combination pills perfectly (use is consistent and always correct) will become pregnant.

In general, if the Pill is used correctly, it's 97 to 99 per cent effective in preventing pregnancy.

But the Pill does not protect against sexually transmitted infections.

Trip to the doctor

Both types of pills require a medical evaluation and prescription. The doctor's appointment is necessary to assess a woman's health and the suitability of the Pill to her situation. There are some risks associated with taking the Pill.

Possible side effects: