When to Start Oral Contraceptive Pills
Oral contraceptive pills can be started at any time during the menstrual cycle if pregnancy is reasonably excluded, but starting within the first 5 days of menstrual bleeding eliminates the need for backup contraception. 1
Combined Oral Contraceptives (COCs)
Optimal Timing for Initiation
Start within the first 5 days of menstrual bleeding: No backup contraception is needed when COCs are initiated during this window. 1
Start after day 5 of menstrual bleeding: Backup contraception (such as condoms) or abstinence is required for 7 consecutive days. 1
Quick Start (any time during cycle): COCs can be started immediately at any point if pregnancy is reasonably excluded, but this requires 7 days of backup contraception. 2, 1
Special Clinical Scenarios
Amenorrhea: COCs can be initiated at any time if pregnancy is excluded, with 7 days of backup contraception required. 1
Postpartum (not breastfeeding): Can start immediately, with backup contraception for 7 days if ≥21 days postpartum and menstrual cycles have not returned. 2, 1
Postabortion: COCs can be started within the first 7 days, including immediately postabortion, without need for backup contraception if started immediately. 2
Critical Evidence on Timing
Research demonstrates that delaying COC initiation beyond day 5 increases ovulation risk, particularly with lower-dose formulations. When 20-mcg ethinyl estradiol pills were started on day 7 versus day 1, there was a statistically significant increase in ovulation (8 of 78 women ovulated when starting on day 7 versus 0 of 77 when starting on day 1, p=0.006). 3 However, no ovulations occurred when COCs were started at follicle diameter ≤10 mm (mean cycle day 7.6). 4
Progestin-Only Pills (POPs)
Optimal Timing for Initiation
Start within the first 5 days of menstrual bleeding: No backup contraception is needed. 1
Start after day 5 of menstrual bleeding: Backup contraception or abstinence is required for only 2 days (not 7 days like COCs). 2, 1
Key Advantage of POPs
POPs require only 2 days of backup contraception when started late in the cycle, compared to 7 days for COCs, due to the rapid onset of contraceptive effects on cervical mucus. 1 Peak serum steroid levels are reached approximately 2 hours after administration, and an estimated 48 hours of POP use achieves contraceptive effects on cervical mucus. 2
Special Clinical Scenarios
Amenorrhea: POPs can be started at any time if pregnancy is excluded, with 2 days of backup contraception. 1
Postpartum: Can be started immediately postpartum (≥21 days), including in breastfeeding women, with 2 days of backup contraception if menstrual cycles have not returned. 2
Postabortion: POPs can be started within the first 7 days, including immediately, with 2 days of backup contraception unless started at the time of surgical abortion. 2
Critical Practice Points
Avoiding Delays
The CDC and ACOG strongly advise against delaying contraceptive initiation until the next menstrual period, as this increases the risk of unintended pregnancy. 1 Women can start immediately with appropriate backup contraception rather than waiting.
When Pregnancy Status is Uncertain
When uncertainty exists about pregnancy status, the benefits of starting OCPs likely exceed any risk; therefore, starting should be considered at any time, with a follow-up pregnancy test in 2-4 weeks. 2
Switching from Another Method
OCPs can be started immediately when switching from another contraceptive method without waiting for the next period, though backup contraception requirements depend on when in the cycle the switch occurs (7 days for COCs, 2 days for POPs if >5 days since menstrual bleeding started). 2, 1
No Examinations Required
Among healthy women, no examinations or tests are needed before OCP initiation, though baseline weight and BMI measurement may be useful for monitoring. 2