Final answer:
Birth control pills typically begin to protect against pregnancy after 7 days of use, while emergency contraception is most effective within 72 hours after unprotected sex. It's important to note that postpartum women are advised to wait three to six weeks before starting certain hormonal contraceptives.
Step-by-step explanation:
The time it takes for oral contraceptives to start working can vary depending on the type of contraceptive and the timing of initiation related to the menstrual cycle.
For most birth control pills, which consist of either the combined pill (containing both estrogen and progesterone) or the progesterone-only pill, protection from pregnancy begins after 7 consecutive days of taking the pill.
It's recommended to use another form of contraception, such as condoms, during the first week of pill use. If pills are started within five days of the start of a woman's period, they will protect against pregnancy straight away.
Emergency contraception should be taken as soon as possible after unprotected sex and is most effective when taken within 72 hours. It works by stopping ovulation or preventing fertilization.
Ovulation is not disrupted if it has already occurred, which is why timing is crucial. Emergency contraception is available over-the-counter for individuals 17 and older.
Lastly, for those who are postpartum, recommendations advise waiting at least three weeks after giving birth before starting a contraceptive method containing both estrogen and progestin, with a six-week waiting period suggested for individuals with additional risk factors for blood clots.