Yes, you can take Plan B while breastfeeding. Plan B contains levonorgestrel, a progestin-only hormone that passes into breast milk in small amounts and is generally considered compatible with breastfeeding.
You do not need to stop breastfeeding or discard breast milk after taking Plan B. Available evidence has not found harmful effects on breastfeeding or on the health, growth or development of breastfed babies after levonorgestrel use.
Emergency contraception works best when taken as soon as possible after unprotected sex. If you are considering ella (ulipristal acetate) instead of Plan B, its FDA labeling states that small amounts also pass into breast milk, but there is limited information about its effects on breastfed babies or milk production.
Exclusive breastfeeding can reduce the chance of pregnancy during the first 6 months after giving birth, but only if your period has not returned and you are breastfeeding frequently, including overnight. Because these conditions can change, breastfeeding should not automatically be relied on as your only method of birth control.
Talk to your OB-GYN or another healthcare professional if you are unsure which emergency contraceptive is best for you, especially if you take other medications that could make levonorgestrel less effective.