Bioidentical Progesterone: How It Works in the Body

Progesterone is a steroid hormone made in both women and men. It is often discussed only in the context of pregnancy, but it acts on the brain, the immune system, fluid balance and the way tissues respond to oestrogen. This article explains how progesterone works in the body, how bioidentical progesterone differs from synthetic progestins, and what a doctor checks before prescribing it.

Where does progesterone come from?

Progesterone is made from pregnenolone, which the body makes from cholesterol. Before menopause, most of a woman's progesterone comes from the corpus luteum, the structure left in the ovary after ovulation. The adrenal glands make smaller amounts in women and men.

What does progesterone do in the body?

• Calming signals in the brain. The body converts progesterone into allopregnanolone, which modifies signalling at GABA-A receptors, the brain's main calming receptors. Clinical effects depend on the formulation, route and individual response.

• Fluid balance. Progesterone opposes aldosterone, a hormone that makes the kidneys hold on to salt and water.

• Balancing oestrogen's effects. Progesterone counters oestrogen's growth signal on some tissues.

• Immune signalling. Progesterone influences how immune cells communicate.

What does "bioidentical" mean?

Bioidentical progesterone has the same molecular structure as the progesterone the body makes. Synthetic progestins are different molecules that act on progesterone receptors and can also act on other receptors. Bioidentical describes the molecule, not how a product is approved or made, so doctors check the exact product, its approval or licensing status in India and its quality.

How is progesterone given?

Progesterone can be taken by mouth, applied to the skin, or given vaginally. Each route behaves differently. Skin-applied progesterone cream or oil must not replace the prescribed regimen that protects the lining of the uterus when systemic oestrogen is given. Symptom improvement or hormone levels cannot show that this protection is in place, and saliva tests should not guide dosing. The dose, route and schedule are set by the prescribing doctor for each person; they are not something to copy from an article.

What do doctors check first?

• the reason for considering progesterone, and the person's history and examination

• whether oestrogen is also being prescribed: when systemic oestrogen is given to a woman with a uterus, the lining of the uterus needs protection with an adequate progestogen, chosen and dosed according to current menopause guidance

• pregnancy or plans for pregnancy

• a history of breast cancer or other hormone-sensitive cancer, blood clots, liver disease or unexplained vaginal bleeding

• current medicines, including sedatives

• previous stroke or heart attack, inherited clotting risk, and allergies to any ingredient of the product

Suitability depends on the complete regimen, not on progesterone alone.

What side effects can occur?

Possible effects include drowsiness, dizziness, headache and breast tenderness. Do not drive if you feel drowsy or dizzy. Unexpected vaginal bleeding needs medical assessment. Risks depend on the product, dose, route and the person, which is why progesterone is prescribed and reviewed by a doctor.

Prescribing in practice

Prescribing progesterone requires an individual assessment and follow-up.

Related guides

• Bioidentical hormone therapy guide

• Peptide therapy guide

• Low-dose naltrexone guide

Sources

1. Indian Menopause Society. Clinical practice guidelines on menopause, 2026. https://pmc.ncbi.nlm.nih.gov/articles/PMC12948155/

2. The 2022 hormone therapy position statement of The North American Menopause Society. Menopause 2022;29(7):767–794.

3. Genazzani AR et al. Progesterone, progestagens and the central nervous system. Human Reproduction 2000;15(Suppl 1):14–27. https://pubmed.ncbi.nlm.nih.gov/10928416/

4. Prior JC. Progesterone for symptomatic perimenopause treatment. Facts, Views & Vision in ObGyn 2011;3(2):109–120. https://pubmed.ncbi.nlm.nih.gov/24753856/