J.M.J.

Oral Contraceptives or Birth Control Pills?

Pharmacists For Life Canada, Box 43508, 180 James Street, S., Hamilton, Ontario L8P 4V0

The term “Oral Contraceptive” implies that this is something that is taken by mouth (oral) and is against (contra) conception. It was the original name given to the hormonal medicine taken by women to cause temporary infertility by preventing conception (fertilization) from occurring. This term was accurate at the time because the concentration of the female steroid hormone “estrogen” contained in these pills was sufficient to prevent ovulation (release of a female egg). When ovulation was prevented there was no chance that conception could occur. The term however is not entirely accurate for most of the present day pills.

Use of oral contraceptives over a period of time revealed that they caused some serious side effects, particularly the formation of dangerous blood clots (thromboembolic disease). Estrogen was the agent implicated and so to reduce the occurrence of side effects the tablets were reformulated to contain less estrogen. Lower estrogen however caused an important change in effect: ovulation sometimes takes place and thus the female egg may become fertilized i.e. conception may occur. If conception occurs then the tablets cannot be accurately called “contraceptives”.

The use of the newer formulation of pills is still considered to be effective in preventing birth because even if fertilization occurred the living embryo will be eliminated by another effect. The lining of the woman's uterus is changed by these pills in a way that does not allow the embryo to attach and receive nourishment. At an age of 1 or 2 weeks the embryo will be removed from the body in a menstrual type bleeding. This mechanism is more accurately termed abortifacient. Thus although the present day pills are effective in preventing birth (birth control pills) it is estimated that they do this by causing an abortifacient effect in 2 to 10% of cycles.