It is one of the most effective reversible methods of birth control available.
Most pills contain a combination of estrogen and progesterone, the two main female hormones.
Modern pills have very low doses of these hormones and cause very few, if any, side effects. Condoms must be used to help protect against these. The ovaries stop releasing eggs. The cervical mucus thickens and inhibits the sperm from being able to pass through the cervix into the uterus and fallopian tubes. The lining of the uterus does not develop enough for a fertilized egg to implant and start a pregnancy.