Progesterone is produced in several places throughout the body, with the ovaries being the primary source in women of reproductive age. It is also made by the placenta during pregnancy, by the adrenal glands in both sexes, by the testes in men, and even by the brain. All progesterone, regardless of where it’s made, starts from the same raw material: cholesterol.
How the Body Builds Progesterone From Cholesterol
Every steroid hormone in your body traces back to cholesterol, and progesterone is no exception. Cholesterol is first converted into a compound called pregnenolone, which then undergoes two quick chemical changes: a dehydrogenation step followed by a rearrangement of its molecular structure. The result is progesterone. This same pathway runs in every tissue that produces the hormone, from the ovaries to the adrenal glands to the brain.
Progesterone also serves as a building block for other hormones. Your body uses it as an intermediate step to produce cortisol (your stress hormone), aldosterone (which regulates blood pressure), and even testosterone and estrogen. That makes progesterone one of the most foundational hormones in the entire steroid family tree.
The Ovaries: The Main Source During the Menstrual Cycle
In women who are menstruating, the ovaries are the dominant source of progesterone, and the amount they produce swings dramatically depending on the phase of the cycle. During the first half (the follicular phase), progesterone levels are very low, typically 0.1 to 0.7 ng/mL. After ovulation, a temporary gland called the corpus luteum forms from the remains of the follicle that released the egg. This structure ramps up progesterone production significantly, pushing levels to 2 to 25 ng/mL during the second half of the cycle (the luteal phase).
The trigger for this surge is luteinizing hormone, or LH. A spike in LH near the end of the follicular phase signals ovulation and kicks the corpus luteum into gear. If no pregnancy occurs, the corpus luteum breaks down after about 10 to 14 days, progesterone drops, and the uterine lining sheds as a period. If an embryo implants, the corpus luteum keeps producing progesterone to sustain the early pregnancy.
The Placenta Takes Over During Pregnancy
The corpus luteum can’t maintain progesterone production forever. Around 6 to 8 weeks of pregnancy, a critical transition happens: the placenta gradually takes over as the primary progesterone factory. This event, known as the luteal-placental shift, occurs as the corpus luteum winds down and specialized placental cells called trophoblasts scale up their output. From that point forward, placental progesterone continues to rise steadily all the way to delivery.
The timing of this handoff can vary. In twin pregnancies, the shift is delayed, with the corpus luteum staying active longer and the transition stretching closer to 10 to 12 weeks. This is partly because twin pregnancies produce higher levels of the hormone (hCG) that keeps the corpus luteum functioning. Once the placenta fully takes charge, it produces progesterone in quantities far beyond what the corpus luteum ever could, helping maintain the uterine lining, suppress contractions, and support fetal development until birth.
Progesterone in Men
Progesterone is not exclusively a female hormone. Men produce it too, primarily in the testes and adrenal glands, though in much smaller amounts. Inside the testes, both Leydig cells (which are better known for making testosterone) and immune cells called interstitial macrophages contribute to progesterone production. Recent research suggests these macrophages produce progesterone as part of a local feedback loop: testosterone from Leydig cells stimulates the macrophages to make progesterone, which in turn helps regulate testosterone production. It’s a finely tuned back-and-forth system.
In men, progesterone also acts as a precursor for other hormones and plays a role in sperm development and brain function.
The Brain Makes Its Own Supply
One of the more surprising sources of progesterone is the nervous system itself. Both the brain and peripheral nerves can synthesize progesterone locally, earning it the label “neurosteroid.” Rather than relying entirely on progesterone circulating through the bloodstream, nerve tissue produces its own to regulate specific functions on the spot.
Locally produced progesterone in the nervous system influences neurotransmission and plays a key role in the formation and repair of myelin, the protective insulation around nerve fibers. This has made it a topic of interest for conditions involving nerve damage or demyelination. Peripheral nerves, which have a strong capacity for regeneration, appear to use locally made progesterone to support their repair processes.
The Adrenal Glands
Sitting on top of each kidney, the adrenal glands produce small amounts of progesterone in both men and women. This is a secondary source compared to the ovaries or placenta, but it becomes more relevant after menopause, when the ovaries largely stop producing the hormone. The adrenals follow the same cholesterol-to-pregnenolone-to-progesterone pathway, and much of the progesterone they make is quickly converted into cortisol and other adrenal hormones rather than being released as progesterone itself.
Where Pharmaceutical Progesterone Comes From
The progesterone used in hormone therapy and medications is not extracted directly from human tissue. It is synthesized in a lab, but the starting material comes from plants. A compound called diosgenin, found abundantly in wild yam species (especially from the genus Dioscorea) and fenugreek, serves as the raw material. Diosgenin is extracted from these plants through a process that breaks down larger plant compounds using acid, base, or enzyme catalysts. From there, chemists convert it through a series of steps into pregnenolone and then into progesterone.
This plant-derived, lab-synthesized progesterone is chemically identical to what your body produces, which is why it’s called “bioidentical” progesterone. It’s worth noting that simply eating wild yam will not raise your progesterone levels. Your body cannot convert diosgenin into progesterone on its own. That conversion requires industrial chemical processing. Products marketed as “natural progesterone creams” derived from wild yam that haven’t undergone this conversion don’t contain actual progesterone.