Progesterone is a steroid hormone your body makes from cholesterol. It plays a central role in the menstrual cycle, pregnancy, and dozens of other processes, from mood regulation to bone health. Both men and women produce it, though it’s most recognized for its reproductive functions in women.
Where Progesterone Comes From
Your body produces progesterone primarily in two places: the adrenal glands (small glands sitting on top of each kidney) and the gonads (ovaries in women, testes in men). In women who are cycling, the biggest source is the corpus luteum, a temporary structure that forms in the ovary after an egg is released each month. During pregnancy, the placenta eventually takes over as the main production site.
Chemically, progesterone is a 21-carbon molecule derived from cholesterol, which makes it part of the same steroid hormone family as estrogen and cortisol. Because it shares this steroid structure, it works by entering cells and influencing gene activity directly, a slower but longer-lasting process than many other signaling molecules in the body. It also triggers some rapid effects through receptors on cell membranes, which explains why its influence is so wide-ranging.
Its Role in the Menstrual Cycle
Progesterone’s most familiar job is preparing the uterine lining for a potential pregnancy each month. During the first half of the menstrual cycle (the follicular phase), estrogen drives the lining to thicken and grow. After ovulation, progesterone takes the lead. The corpus luteum releases it in rising amounts, and it transforms the uterine lining from a proliferating tissue into a receptive one, ready to accept and nourish an embryo.
This transformation involves real physical changes at the cellular level. The lining’s glands begin accumulating glycogen (stored sugar), the cells become larger and rounder, and the tiny blood vessels in the tissue remodel to support possible implantation. Progesterone also thickens cervical mucus, making it harder for sperm to pass through, which is one reason why fertility awareness methods track cycle phases so closely.
If no embryo implants, the corpus luteum breaks down after about 12 to 14 days, progesterone drops sharply, and the lining sheds as a period. That drop in progesterone is what triggers menstruation.
How It Supports Pregnancy
Progesterone is sometimes called “the hormone of pregnancy,” and for good reason. Its presence is a prerequisite for an embryo to implant in the uterine wall, and its absence causes pregnancy loss. Once implantation occurs, progesterone keeps the uterine lining stable and prevents the muscular wall of the uterus from contracting, a relaxing effect that protects the developing pregnancy.
In early pregnancy, the corpus luteum continues producing progesterone until the placenta is mature enough to take over, usually around weeks 8 to 12. From that point on, progesterone levels climb steadily through all three trimesters, supporting placental function and helping suppress the immune response that might otherwise reject the embryo as foreign tissue.
Progesterone in Men
Men produce progesterone too, just in smaller amounts. The testes and adrenal glands are the primary sources. In men, progesterone serves as a chemical building block. The body converts it into other hormones, including testosterone and cortisol, making it an essential link in the hormone production chain. Its full range of functions in male physiology is still being studied, but it appears to influence mood, sleep, and possibly sperm development.
Normal Progesterone Levels
Progesterone levels swing dramatically depending on where a woman is in her cycle. During the follicular phase (before ovulation), levels are low: roughly 0.2 to 1.5 ng/mL. After ovulation, during the luteal phase, they surge to between 1.7 and 27.0 ng/mL. This massive increase is what blood tests look for when confirming that ovulation has actually occurred. Levels above about 3 to 5 ng/mL in the luteal phase generally indicate that an egg was released.
During pregnancy, levels climb far higher, reaching values many times above the luteal phase range. After menopause, progesterone drops to very low levels because ovulation no longer occurs and the corpus luteum is no longer forming each month.
Signs of Low Progesterone
When progesterone drops below normal, the balance with estrogen tips. Too little progesterone relative to estrogen can produce a recognizable pattern of symptoms:
- Irregular or heavy periods, because the uterine lining builds up excessively without progesterone to counterbalance estrogen’s growth signal
- Difficulty conceiving, since the uterine lining may not be receptive enough for implantation
- Mood changes, anxiety, or depression, reflecting progesterone’s calming influence on the nervous system
- Trouble sleeping, as progesterone has mild sedative properties
- Bloating and weight gain
- Hot flashes, particularly during perimenopause
- Headaches, often linked to hormonal fluctuations
Low progesterone is common during perimenopause, when ovulation becomes inconsistent. It can also occur in younger women due to stress, extreme exercise, or conditions that disrupt ovulation.
Nutrients That Influence Production
A few nutritional factors appear to affect how much progesterone your body makes. Vitamin B6 has the most direct evidence: at supplemental doses, it has been shown to reduce circulating estrogen and increase progesterone, improving the estrogen-to-progesterone ratio. Magnesium also plays a supporting role, particularly in glucose regulation and reducing symptoms tied to the second half of the menstrual cycle. High intake of refined sugar and excessive dairy consumption has been associated with hormonal patterns that feature elevated estrogen and lower progesterone.
Chronic stress is another commonly cited factor. Because both cortisol (the stress hormone) and progesterone are built from the same cholesterol-derived precursors, the theory is that sustained stress diverts raw materials toward cortisol production at progesterone’s expense. While the precise mechanics are still debated, the clinical pattern of stress-related cycle disruption is well established.
Medical Uses of Progesterone
Supplemental progesterone is prescribed for a range of conditions. The most common include supporting the luteal phase during IVF cycles, preventing early pregnancy loss in women with a history of miscarriage, treating irregular or absent periods, managing endometriosis, relieving premenstrual syndrome, and protecting the uterine lining in women taking estrogen therapy during menopause. In menopausal hormone therapy, progesterone’s primary job is to prevent the uterine lining from overgrowing in response to estrogen, which could otherwise raise the risk of uterine cancer.
Bioidentical vs. Synthetic Progesterone
Not all prescription progesterone is the same. Micronized progesterone is a bioidentical form, meaning its molecular structure is identical to what your ovaries produce. Synthetic versions, called progestins, mimic some of progesterone’s effects but have a different chemical structure. Common synthetic progestins include medroxyprogesterone acetate and levonorgestrel (widely used in hormonal birth control).
The distinction matters because synthetic progestins don’t behave identically to natural progesterone in the body. They can bind to receptors for other hormones, including androgen, cortisol, and aldosterone receptors, which is why different progestins carry different side effect profiles. The most clinically significant difference involves breast cancer risk. A systematic review found that estrogen combined with synthetic progestins (particularly medroxyprogesterone acetate) is associated with an increased risk of breast cancer. Bioidentical progesterone combined with estrogen has not shown the same association. In fact, research suggests that natural progesterone may act as a brake on estrogen-driven cell growth in breast tissue, while certain synthetic progestins may promote it.
This is one reason many clinicians have shifted toward prescribing micronized progesterone for menopausal hormone therapy rather than older synthetic progestins, though the choice depends on the specific clinical situation and the form of delivery (oral capsules, vaginal inserts, or topical creams are all available).