When should I start taking birth control pills?

When to Start Birth Control Pills

Birth control pills can be started at any time during the menstrual cycle if it is reasonably certain that the woman is not pregnant, though timing affects the need for backup contraception. 1

Starting Combined Hormonal Contraceptive Pills

Timing Based on Menstrual Cycle

• If started within the first 5 days of menstrual bleeding, no additional contraceptive protection is needed 1, 2
• If started more than 5 days after the start of menstrual bleeding, use backup contraception (e.g., condoms) or avoid sexual intercourse for the first 7 days 1

Starting Methods

• Day 1 Start: Take the first active pill during the first 24 hours of your period; no backup method needed 3, 4
• Sunday Start: Take the first active pill on the Sunday after your period starts (even if still bleeding); use backup method for the first 7 days 3, 4

Special Situations

Amenorrhea (Not Postpartum)

• Can start at any time if reasonably certain not pregnant 1
• Use backup contraception for the first 7 days 1

Postpartum (Breastfeeding)

• Should not use combined hormonal contraceptives during the first 3 weeks after delivery due to increased risk of venous thromboembolism 1
• Generally should not use combined hormonal contraceptives during the fourth week postpartum if breastfeeding 1
• If ≥21 days postpartum and no menstrual cycles yet, use backup contraception for 7 days 1

Postpartum (Not Breastfeeding)

• Should not use combined hormonal contraceptives during the first 3 weeks after delivery 1
• If ≥21 days postpartum, can start pills but use backup contraception for 7 days 1

Postabortion

• Can start within the first 7 days after abortion, including immediately postabortion 1
• Need backup contraception for 7 days unless started at the time of surgical abortion 1

Switching from Another Contraceptive Method

• Can start immediately without waiting for next period 1, 2
• May need backup contraception for 7 days depending on previous method 1

Progestin-Only Pills (POPs)

• Can be started at any time if reasonably certain not pregnant 1
• If started within 5 days of menstrual bleeding, no additional contraception needed 1
• If started >5 days after menstrual bleeding began, use backup contraception for 2 days 1
• POPs have a shorter backup contraception requirement (2 days) compared to combined pills (7 days) 1

Managing Missed Pills

Combined Pills

• If 1 active pill missed: Take as soon as remembered, take next pill at regular time 3
• If 2 active pills missed in Week 1 or 2: Take 2 pills for 2 days, then resume normal schedule; use backup for 7 days 3, 4
• If 2+ active pills missed in Week 3 or 4: Throw out pack and start new pack same day; use backup for 7 days 3

Progestin-Only Pills

• If >3 hours late (traditional POPs): Take pill as soon as remembered and use backup for 2 days 5
• Recent research suggests the 3-hour window may be overly strict for some newer progestin formulations 5

Important Considerations

• Vomiting or diarrhea can reduce contraceptive effectiveness; if severe vomiting/diarrhea occurs, continue taking pills but use backup contraception until 7 days after recovery 1, 3
• Emergency contraception should be considered if vomiting/diarrhea occurred within first week of new pill pack and unprotected intercourse occurred 1, 6
• Taking pills at the same time each day improves effectiveness, especially for progestin-only pills 3, 5
• Typical use failure rates for oral contraceptives are 4-7% per year 7

Common Pitfalls to Avoid

• Waiting for next period to start pills (unnecessary delay in protection) 1
• Not using backup contraception when needed based on start timing 1, 3
• Not having emergency contraception available in case of missed pills or other contraceptive failures 1, 6
• Not accounting for drug interactions that may reduce effectiveness (certain antibiotics, St. John's Wort) 3