Plan B does not meaningfully affect milk supply. Studies on breastfeeding women who took the 1.5 mg levonorgestrel dose found that reductions in lactation were rare and occurred at the same rate as in women who didn’t take it. The drug does pass into breast milk in small amounts, but the concentration is low enough that most guidelines consider it safe to continue nursing with only a brief waiting period, if any.
What Happens in Your Body After Taking Plan B
Plan B contains a single high dose of levonorgestrel, a synthetic form of progesterone. After you take it, levels peak in your blood within one to four hours and in your breast milk within two to four hours. The concentration in milk runs consistently lower than in your blood, averaging about 28% of plasma levels.
This matters because progesterone-based hormones, even at higher doses, don’t suppress prolactin the way estrogen can. Prolactin is the hormone that drives milk production. Since Plan B contains no estrogen, it lacks the biological mechanism that would meaningfully reduce your supply. A single dose clears your system relatively quickly, so any hormonal fluctuation is temporary.
What the Research Shows About Supply
The most direct evidence comes from studies comparing breastfeeding women who used levonorgestrel emergency contraception with those who didn’t. Researchers found that a single 1.5 mg pill did not objectively affect the amount of milk produced. Women in the study group reported no subjective difference in how much milk they were making compared to controls. Broader reviews of progestogen-only contraceptives (the hormone family Plan B belongs to) have reached similar conclusions, finding no harmful effects on breastfeeding or infant outcomes even when started less than six weeks postpartum.
Some women do report a temporary dip in supply after taking Plan B. Anecdotally this comes up often in breastfeeding communities. Stress, disrupted nursing schedules, or simply the anxiety of an unplanned situation can all contribute to a short-term drop that gets attributed to the pill itself. If you do notice a dip, frequent nursing or pumping for a day or two typically brings things back to normal.
How Long to Wait Before Nursing
Expert recommendations on timing vary, which can be confusing. Some sources suggest waiting three to four hours after taking Plan B before breastfeeding, which lines up with when drug levels peak in breast milk. Others recommend waiting eight hours. And some experts say no interruption in breastfeeding is necessary at all.
The National Institutes of Health suggests that waiting three to four hours after taking the dose will lower the amount of levonorgestrel your baby gets through breast milk. If you choose to wait, pump and discard milk during that window to keep your supply stimulated. This is a precautionary measure rather than a response to documented harm. Both the American College of Obstetricians and Gynecologists and the World Health Organization confirm that breastfeeding women can use emergency contraception.
Is the Drug Safe for Your Baby?
The small amount of levonorgestrel that reaches breast milk does not appear to harm nursing infants. In a follow-up study that tracked children for two years after their mothers used levonorgestrel emergency contraception, researchers found no differences in weight, height, head circumference, or cognitive development compared to children whose mothers had not taken the drug. All measurements fell within national growth and development standards.
The milk-to-plasma ratio of 0.28 means your baby is exposed to roughly a quarter of your blood concentration, and your blood concentration itself drops steadily after that initial four-hour peak. For a single-dose medication, the total exposure window is short.
Plan B vs. Ella for Breastfeeding Parents
If you’re choosing between the two main emergency contraceptive pills, the breastfeeding considerations are quite different. Plan B (levonorgestrel) has a well-studied safety profile during lactation, with clear evidence that it doesn’t affect milk supply or infant health. The wait time before nursing is at most a few hours.
Ella (ulipristal acetate) is a different story. The manufacturer recommends avoiding breastfeeding for a full seven days after taking it. The LactMed database, which is generally more conservative in its analysis, recommends at least 24 hours. A fully breastfed infant would ingest an estimated 4.1 micrograms per kilogram of the drug on the first day, with cumulative exposure increasing over five days. There is limited published data on what this means for nursing babies, which is why the recommended wait time is so much longer.
For breastfeeding parents, Plan B is the more practical choice. Pumping and discarding milk for a few hours is manageable. Pumping and discarding for up to a week while maintaining supply is a significant burden, and for parents without a freezer stash, it may not be feasible at all.
Protecting Your Supply After Taking Plan B
If you decide to wait before nursing, the key is to keep removing milk on your normal schedule. Pump or hand express at the times your baby would normally feed, then discard the milk. Skipping sessions during the waiting period is what actually puts your supply at risk, not the pill itself.
Stay hydrated, eat normally, and nurse on demand once you resume. If your baby is younger than six months and exclusively breastfed, they may be fussier than usual during the brief separation from the breast. Having a small amount of previously expressed milk on hand can help bridge the gap. For most women, any perceived change in supply resolves within 24 to 48 hours without any special intervention beyond regular feeding.