Yes, it is safe to take Plan B while on birth control. The active ingredient in Plan B (levonorgestrel) does not interfere with hormonal contraception, and taking both at the same time does not reduce the effectiveness of either one. The most common reason someone on birth control would need Plan B is missed pills, and guidelines specifically recommend it in certain missed-pill scenarios.
Why You Might Need Plan B While on Birth Control
Birth control pills work reliably only when taken consistently. Missing even one or two pills can open a window where pregnancy becomes possible, especially depending on when in your cycle the missed doses happen. That’s where emergency contraception comes in as a backup.
CDC guidelines break it down by how many pills you’ve missed. If you’ve missed one pill (meaning it’s been 24 to 48 hours since you should have taken it), emergency contraception generally isn’t needed. The exception is if you also missed pills earlier in your cycle or during the last week of hormonal pills in your previous pack, which compounds the gap in protection.
If you’ve missed two or more consecutive pills (48 hours or longer since your last dose), emergency contraception is more strongly recommended, particularly if the missed pills were during the first week of your pack and you had unprotected sex within the previous five days. That first-week timing matters because your body hasn’t built up enough hormonal suppression yet to reliably prevent ovulation.
Plan B Won’t Interfere With Your Regular Birth Control
One concern people have is whether taking Plan B will somehow cancel out or weaken their regular pill. It won’t. Plan B contains levonorgestrel, which is actually the same type of synthetic progestin found in many combination birth control pills. Because it doesn’t have anti-progestin properties, it works alongside your regular contraception rather than against it. You’re essentially giving your body an extra surge of a hormone it already recognizes.
This means you can take Plan B and continue your regular pill pack without skipping a beat. The CDC confirms there is no concern that using levonorgestrel emergency contraception at the same time as systemic hormonal birth control decreases the effectiveness of either method.
How to Resume Your Pill After Taking Plan B
You should continue taking your regular birth control pills right away, on your normal schedule. There’s no waiting period before resuming. However, you do need backup protection (like condoms) for seven days after the missed pills, since your regular contraception needs that time to reach full effectiveness again.
If you don’t get a withdrawal bleed within three weeks after taking Plan B, take a pregnancy test. Plan B can sometimes shift the timing of your next period or withdrawal bleed by a few days in either direction, so a slight delay alone isn’t necessarily a sign of pregnancy. But the three-week mark is the point where it’s worth checking.
Plan B vs. Ella: An Important Distinction
This compatibility only applies to Plan B (levonorgestrel). The other emergency contraception pill, Ella (ulipristal acetate), works very differently and is not a good match with hormonal birth control. Ella is a selective progesterone receptor modulator, meaning it blocks progesterone receptors to prevent ovulation. That same blocking action can interfere with the progestin in your birth control pills, potentially reducing their effectiveness for the rest of your cycle.
If you’re on hormonal birth control and need emergency contraception, Plan B is the better choice. CDC guidelines specifically note that Ella should be excluded as an option in missed-pill scenarios for people using hormonal methods. If for some reason you do take Ella, you’d need to use a barrier method like condoms until your next period arrives before relying on your hormonal birth control again.
Weight and Plan B Effectiveness
One factor worth knowing about is body weight. Plan B may become less effective at higher weights. Health Canada has stated that levonorgestrel may be less effective in women over 165 pounds and possibly ineffective over 176 pounds, though other regulatory bodies have pushed back on those cutoffs. A European Medicines Agency review concluded the available data was too limited to draw firm conclusions about reduced efficacy based on weight alone.
The current medical consensus leans toward not discouraging anyone from using Plan B based on weight, since some protection is better than none. But if you weigh over 165 pounds and want the most reliable emergency option, a copper IUD inserted within five days of unprotected sex is the most effective form of emergency contraception regardless of body weight.
Side Effects to Expect
Taking Plan B on top of your regular birth control means your body is processing a higher-than-usual dose of synthetic progestin. Common side effects include nausea, fatigue, headache, and breast tenderness. Some people experience spotting or light bleeding in the days after taking it. These effects are temporary and typically resolve within a day or two.
Your next withdrawal bleed might come a few days early or late. If it’s heavier or lighter than usual, that’s also within the range of normal. None of these changes affect your ongoing protection once you’ve been back on your regular pills for a full week.