What is Progesterone?

Progesterone is one of the most important hormones in the story of lactation — not because it promotes milk production, but because it actively suppresses it. Understanding what progesterone does, and what happens when it drops, is essential for anyone pursuing induced lactation.

What Progesterone Does

Progesterone is a steroid hormone produced primarily by the ovaries (specifically the corpus luteum after ovulation) and, during pregnancy, by the placenta. It plays a central role in the menstrual cycle and pregnancy: preparing the uterine lining for implantation, maintaining pregnancy, and — critically for our purposes — preparing breast tissue for eventual milk production while simultaneously preventing that production from starting too early.

During pregnancy, progesterone levels rise dramatically. This rise signals the breast tissue to develop — ducts branch, alveoli (milk-producing cells) multiply, blood supply increases. The breasts are literally being built to produce milk. But at the same time, progesterone inhibits the prolactin receptors that would trigger actual milk production. It's like building a factory while keeping it switched off.

The Progesterone Drop and Milk Production

After birth, the placenta is delivered and progesterone levels plummet. This sudden drop removes the inhibition on prolactin receptors, and — combined with the prolactin that's been building throughout pregnancy — triggers the onset of milk production. This is why milk "comes in" a few days after birth, not during pregnancy despite months of breast tissue development.

This mechanism is the foundation of the Newman-Goldfarb protocols for induced lactation. The protocols use a combination birth control pill (which contains synthetic progesterone and estrogen) for 60-90 days to mimic the hormonal environment of pregnancy. The pill is then abruptly stopped, creating an artificial progesterone drop that triggers the same cascade — prolactin receptors activate, and milk production begins. Pumping and nursing then maintain and build supply through the normal supply-and-demand loop.

Progesterone and the Menstrual Cycle

Even outside of pregnancy protocols, progesterone affects lactation through the normal menstrual cycle. After ovulation (the luteal phase), progesterone rises. Many nursing women notice a dip in milk supply in the days before their period — this is progesterone doing exactly what it does during pregnancy: partially suppressing prolactin's effect.

When the period arrives and progesterone drops, supply typically recovers. This cyclical pattern is normal and expected. Understanding it helps — if your supply dips predictably every month, you know it's hormonal rather than something you're doing wrong. For more detail on this pattern, see our guide on how your menstrual cycle changes when nursing.

Progesterone-Based Contraceptives and Lactation

This is where progesterone becomes directly relevant for many women in ANR. Progestin-only contraceptives (the mini-pill, hormonal IUDs, the implant) are generally considered compatible with lactation — in fact, they're often the recommended contraceptive for breastfeeding mothers. The doses are low enough that they don't significantly suppress prolactin.

Combined contraceptives (containing both estrogen and progestin) are a different story. The estrogen component, particularly at higher doses, can significantly reduce milk supply. This is why the Newman-Goldfarb protocol specifically uses the combined pill during the preparation phase and then stops it — the combination prepares the tissue, and stopping it triggers production.

If you're taking hormonal contraception and pursuing lactation, the type and dose matter significantly. See our detailed guide on ANR and hormonal birth control for specific guidance.

Natural Ways to Support Healthy Progesterone Levels

For general reproductive health — not specifically for lactation protocols — healthy progesterone levels are supported by:

• Adequate intake of vitamins B6 and C, which are involved in progesterone production
• Zinc-rich foods like shellfish, seeds, and legumes
• Managing stress — cortisol competes with progesterone for the same precursor molecules, so chronic stress can reduce progesterone levels
• Maintaining a healthy body weight — both very low and very high body fat can affect hormone balance

The Key Takeaway

Progesterone's relationship to lactation is counterintuitive: it helps build the machinery for milk production while simultaneously preventing that machinery from turning on. Understanding this duality — and the power of the progesterone drop — explains why certain induction protocols work the way they do, why supply fluctuates with your cycle, and why some contraceptive choices matter more than others when you're pursuing ANR.

Note: Progesterone supplements and protocols involving hormonal contraceptives are prescription medications. Discuss any hormonal approach to lactation induction with a qualified healthcare provider.