Overview
Progesterone is a single small molecule made from cholesterol with the help of thyroid and vitamin A. It is the direct anti-estrogen, blocking aromatase to stop estrogen production, knocking out the protein that keeps estrogen inside cells, blocking the enzymes that concentrate estrogen, and activating the enzymes that eliminate it. It is anti-inflammatory, anti-fibrotic, anti-excitotoxic, and anti-stress; it acts on the GABA system through its metabolite allopregnanolone the way Valium does; it can replace the entire output of the adrenal glands if they are removed; and it is the basic chemical of fertility and pregnancy. It is also extraordinarily safe, with large doses producing deep sleep rather than toxicity. The reason it has been so consistently suppressed and misrepresented by the drug industry is precisely that it is a single, unpatentable molecule that cures conditions which are worth tens of billions of dollars a year to keep treated rather than cured.
Key Points
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Progesterone is an anti-estrogen through seven to nine specific molecular mechanisms. It destroys the protein that keeps estrogen in the cell, inhibits aromatase (which makes new estrogen), blocks the sulfatase and glucuronidase enzymes that allow estrogen to condense in the cell, and activates the enzymes that eliminate estrogen. Inside an inflamed cell, nine distinct things happen under progesterone's influence to release estrogen and stop its production. The popular "synergy" narrative is wrong; progesterone neutralises and eliminates estrogen in a very absolute sense.
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It is made from cholesterol via pregnenolone, with thyroid and vitamin A as required cofactors. When thyroid is low, cholesterol levels rise because the conversion to progesterone is stalled. The brain is the most intense progesterone factory in the non-pregnant body. The skin is also a major producer, while the ovaries and placenta become the dominant source during pregnancy. Polyunsaturated fats are anti-thyroid, pro-estrogen, and anti-progesterone, which is why diet has to be addressed before supplementation makes consistent sense.
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Progesterone can substitute for the entire output of the adrenal glands. When Hans Selye removed the adrenals from rats, a slight stress would kill them within days. Pregnant females survived until they bore a litter, which gave Selye the idea to test progesterone supplementation; rats with no adrenals at all lived a normal lifespan on progesterone, with no signs of cortisol or aldosterone deficiency. Progesterone has intrinsic anti-cortisol effects at the high end and aldosterone-like effects at the low end, so it both fills in for a deficiency and protects against toxic excess.
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It is always anti-glucocorticoid; it does not raise cortisol. A big dose of progesterone inhibits adrenal cortisol production and lowers ACTH so the pituitary stops driving the adrenals. The medical claim that progesterone can raise cortisol in stressed people is wrong; the only thing it does in stressed animals is bring elevated cortisol back down to normal.
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Progesterone is a direct cortisol receptor antagonist with the same affinity as cortisol itself. It inhibits 11-beta-HSD1, the enzyme that synthesises cortisol, while simultaneously increasing the activity of 11-beta-HSD2, which deactivates cortisol. Human studies show 100 to 200 milligrams orally as a single dose, even in non-optimal powder form, drops both cortisol and adrenaline by roughly 60% in both sexes, with blood pressure falling as a side effect.
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It acts on the GABA-A receptor through its metabolite allopregnanolone, imitating Valium. This is why a big dose can stop a migraine in two or three minutes, why it ends epileptic seizures, and why it produces deep sleep at high doses. One man's son with nightly nocturnal seizures stopped seizing the night he started 30 milligrams of progesterone at bedtime and went a full month without another. Twenty milligrams of oral progesterone tripled allopregnanolone in one study.
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A single dose can resolve crisis conditions and prime the body to make its own. Migraines, epileptic seizures, threatened miscarriage with bleeding, brain trauma in the first day, acute arthritis flares, ovarian cysts, and cardiac arrhythmias have all responded to one dose. The principle is not replacement: when the body gets the right amount at one moment, the thyroid, gonads, skin, and brain return to producing enough progesterone on their own. This makes progesterone a stress-correction agent rather than a hormone to be taken indefinitely.
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The 1946 medical claim that stomach acid destroys progesterone is false. The substance is so resistant to acid that the manufacturing process involves boiling it in concentrated acid to remove other things. The myth was introduced after estrogen-selling drug companies realised progesterone was unpatentable and competed with their main product. Oral progesterone dissolved in vitamin E enters the bloodstream as part of the chylomicrons that absorb dietary fat, bypassing the liver's first-pass metabolism, and produces normal blood levels within an hour.
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Vitamin E and progesterone are inter-soluble; transdermal absorption is only 10 to 20 percent. The Progest-E formula was developed in the 1970s as a way to get doctors past the indoctrination that progesterone could not be taken orally. On the skin, the keratin and sebum bind progesterone and shed it; oral dosing is several times more economical for the same systemic effect. Adding olive oil to the skin first speeds absorption noticeably, demonstrated on a woman with arthritic hands who could flex one hand within an hour after the olive-oil-augmented application.
Notable Quotes
"Progesterone is an anti-estrogen in a very absolute sense. It knocks out the protein that keeps it in the cell."
[Ray Peat — East West Healing: Estrogen vs Progesterone (March 2011)]
"It'll stop a migraine sometimes in two minutes with a big dose (if you have the back up of supporting thyroid function)."
[Ray Peat — East West Healing: Estrogen vs Progesterone (March 2011)]
"It's always anti-glucocorticoid."
[Ray Peat — Wise Lyfe Family Wellness Podcast: The Estrogen Industry, The Magic of Progesterone, and the Importance of Thyroid (January 2022)]
"The drug companies first realized that the progesterone and DHEA were terrible drugs because they tend to cure diseases."
[Ray Peat — Generative Energy #82: What's More Toxic, PUFA or Endotoxin?]
"100 to 200 milligrams orally (single dose) is sufficient to drop cortisol and adrenaline by about 60%."
[Georgi Dinkov — Stress & Weight Gain, Estrogen & Endotoxins w/ Georgi Dinkov]
"If you don't want to take thyroid, progesterone is probably the closest you can get to getting the effects of thyroid without actually using thyroid."
[Georgi Dinkov — How to Utilize and Balance Carbohydrate Intake]
Important Things To Consider
The synthetic "progestins" in birth control pills and HRT are not progesterone. They were given the name "progestins" by drug companies in the late 1940s to trade on progesterone's reputation, but most of them are actually estrogenic and several actively terminate pregnancy. Bioidentical progesterone has none of the cancer, stroke, dementia, blood clot, or heart disease signal that the Women's Health Initiative found for estrogen plus synthetic progestin.
Continuous progesterone use for more than two weeks gradually activates the liver's excretory enzymes. After a month or two of continuous dosing, the liver clears it so quickly that each dose has a much smaller and shorter effect. The natural cycle of about two weeks on, two weeks off matches the body's own rhythm and lets the liver recover. A woman on 200 to 300 milligrams continuously for six months developed hyperadrenaline symptoms and resolved them when stopping.
Low-thyroid people may not respond to small amounts of progesterone. A teaspoonful of the vitamin E solution is not enough to produce an effect if thyroid function is poor. The first thing to fix is temperature and pulse rate via calcium, vitamin D, and thyroid; only then is the system sensitive to physiological doses. If progesterone produces breast pain or feeling worse, low thyroid is the most common reason.
A large dose in men produces a temporary "cold shower" effect that passes in one or two days. Big doses can transiently shrink the penis and lower libido. With proper dosing, the long-term effect is the opposite: progesterone prevents testosterone from being wasted to estrogen via aromatase, supports thyroid secretion, and tends to raise libido rather than lower it. This is one of the reasons Ray warned men away for many years before clarifying the dosing.
Pure crystalline progesterone is largely metabolised at the intestinal wall. The intestinal cells have the same glucuronidation enzymes the liver does, so much of a powder dose is processed and inactivated on the way in. Dissolving progesterone in vitamin E lets it ride along with the chylomicrons that absorb dietary fat into the lymphatics, bypassing this first-pass loss and reaching the bloodstream as intact molecules.
Some progesterone powder is sold with a carbohydrate wetting agent that is not listed as an ingredient. This is a potential toxin and a reason to source from suppliers known for purity. With a clean source, large doses are well tolerated; the toxicity ceiling is so high that Selye's technicians thought rats were dead from massive doses and Selye photographed the animals draped over his hand "like a wet dishrag," merely deeply sedated.
The threshold dose to actually have a progesterone effect is higher than many people use. Ray watched patients try estrogen-style transdermal patches the size of a quarter and report no effect because they were getting essentially zero progesterone into the body. Watch for objective signs (rising temperature, lower resting heart rate with higher stroke volume, better sleep) rather than assuming any small dose is doing the work.
In males with already-low androgens, progesterone can decrease libido or interfere with androgen uptake. This shows up as numbness, lethargy, or reduced libido. Adding 5 milligrams of DHEA daily resolves the problem and allows the anti-cortisol and anti-estrogen effects to come through cleanly. For males generally, pregnenolone is often the safer first choice because it is not anti-androgenic.
Cycling women should not take progesterone during the luteal phase. The body is already producing plenty during that phase. Use it during the first two thirds of the cycle, or if not cycling at all, take it daily. Higher doses during the luteal phase can disrupt normal cycling.
Sedation is the marker for an excessive dose. A hefty dose of progesterone produces symptoms indistinguishable from legal drunkenness, because allopregnanolone is essentially the same kind of GABA agonist as alcohol. Do not drive or operate machinery on a high dose. If sedation hits during the day, you have taken too much for daytime use, so shift to evening dosing.
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