Human fertility is naturally controlled by hormones. Scientists understand the role of hormones in the menstrual cycle and fertility so well, that they have been able to develop medication to artificially control fertility, using hormonal forms of contraception.
Oral contraceptives are more than 99% effective if taken correctly and can reduce the risk of certain cancers.
However, there are possible side effects, such as changes in weight, mood and blood pressure, due to high levels of oestrogen. The pills also do not protect against sexually transmitted communicable diseases. Modern pills contain much less oestrogen.
Contraceptive injections, implants or skin patches contain slow-release progesterone to inhibit the maturation and release of eggs.