Birth control that contains estrogen can significantly reduce your breast milk supply, but it won’t necessarily dry it up completely. In one clinical trial, women using a combined pill (which contains both estrogen and progestin) saw their milk volume drop by about 42% over 18 weeks. Progestin-only methods, on the other hand, showed minimal impact on supply. The type of birth control you choose matters far more than whether you use birth control at all.
Why Estrogen Reduces Milk Supply
Breast milk production depends on the hormone prolactin. Estrogen directly interferes with prolactin’s ability to stimulate milk-making cells in the breast. Lab studies on primate mammary tissue found that estrogen at normal physiological levels blocked prolactin’s effect by roughly 38 to 58%, depending on how it was measured. Estrogen doesn’t shut down milk production on its own; it specifically counteracts prolactin’s signal to produce milk proteins. This is the same mechanism that naturally keeps milk production low during pregnancy, when estrogen levels are high.
Once a baby is born and estrogen drops, prolactin can do its job. Introducing estrogen back through a combined birth control pill, patch, or ring recreates that interference.
Combined Pills, Patches, and Rings
Any contraceptive that includes estrogen falls into the “combined hormonal” category. This includes combination birth control pills, the patch, and the vaginal ring. These methods carry the highest risk to milk supply among all contraceptive options.
In a randomized trial comparing combined pills (containing 30 micrograms of ethinyl estradiol) to progestin-only minipills and non-hormonal controls, the results were stark. Combined pill users experienced a 41.9% decline in milk volume. Progestin-only users saw a 12% decline. Women using no hormonal method saw only a 6.1% decline, which reflects the natural tapering that happens as babies begin eating solid foods.
That said, one double-blind trial that started both combined and progestin-only pills at two weeks postpartum found no significant difference in breastfeeding continuation rates at eight weeks or six months. About 64% of women in both groups were still breastfeeding at the eight-week mark. Among those who stopped, roughly half in each group cited a perceived lack of milk as the reason. So while combined pills do reduce measurable milk volume, the real-world effect on whether breastfeeding continues is less clear-cut and likely depends on how well-established your supply is, how often you nurse, and your individual sensitivity to hormonal changes.
Progestin-Only Methods
Progestin-only options include the minipill, the hormonal IUD, and the arm implant. These methods do not contain estrogen, and the evidence consistently shows they have little to no effect on milk production.
The hormonal IUD and the implant have been compared directly to the copper (non-hormonal) IUD in breastfeeding women. Researchers found no differences in how long women continued breastfeeding at six months. One study noted slightly more breastfeeding episodes on day four after implant placement compared to the copper IUD, but the difference disappeared after that.
Progestin-only pills are traditionally the first-choice oral contraceptive for breastfeeding women. If you’re concerned about supply, many clinicians suggest trying a progestin-only pill for a month or more before committing to a longer-acting method like an implant or injection. The logic is simple: if a pill does affect your supply, you can stop taking it and your production can recover. With an injection, you’d have to wait for it to wear off. With an implant, you’d need an appointment for removal.
Emergency Contraception
Levonorgestrel emergency contraception (the most common type) is a single high dose of progestin. Studies have confirmed it does not meaningfully reduce milk supply. Some guidance suggests pumping and discarding milk for 3 to 8 hours after taking it, but other experts say there is no need to interrupt breastfeeding at all. Reductions in lactation were rare and no different from control groups.
Ulipristal acetate, the other type of emergency contraception, is a different story. There is almost no published data on its effects on breast milk or nursing infants. The manufacturer recommends avoiding breastfeeding for seven days after taking it, though some databases suggest 24 hours is sufficient. If you’re actively breastfeeding and need emergency contraception, the levonorgestrel type is the better-studied option.
The Copper IUD Has No Effect
The copper IUD contains no hormones at all, and extensive research confirms it does not affect milk production, breastfeeding frequency, or the composition of breast milk. Studies have measured copper levels in milk before and after insertion and found no difference. Protein, fat, and sugar content of the milk also stayed the same across multiple trials lasting up to seven months. For someone who wants maximum contraceptive effectiveness with zero risk to their supply, it is the most straightforward choice.
How to Tell if Your Supply Is Dropping
If you start any hormonal contraceptive and worry it’s affecting your milk, watch your baby rather than your breasts. The clearest signs of a true supply problem show up in the infant: increased fussiness or hunger cues after feeding, fewer wet and dirty diapers than usual, and slowed weight gain. A baby who is gaining weight on track and producing plenty of wet diapers is getting enough milk, regardless of how your breasts feel.
If you do notice these signs after starting a new contraceptive, talk to your prescriber about switching methods. Supply can recover after stopping an estrogen-containing method, though the timeline varies. The sooner you catch a decline and make a change, the easier recovery tends to be. Frequent nursing or pumping during the transition helps signal your body to ramp production back up.