Micronized progesterone
Micronized progesterone (Prometrium) is the FDA-approved bioidentical oral progesterone used in HRT to protect the uterine lining and improve sleep.
How it works
Prometrium is the brand name for FDA-approved oral micronized progesterone — the form most often prescribed in bioidentical hormone therapy. 'Micronized' refers to the particle size, which improves oral absorption. It is chemically identical to the progesterone produced by the ovaries (hence 'bioidentical'), unlike synthetic progestins such as medroxyprogesterone acetate or norethindrone. Because it is FDA-regulated, its potency and purity are standardized — this is the key reason FDA-approved micronized progesterone is preferred over compounded progesterone, which lacks that regulatory oversight.
The most clinically distinctive feature of micronized progesterone is its sleep benefit. Unlike synthetic progestins, it metabolizes into neurosteroids (allopregnanolone and pregnanolone) that act as positive allosteric modulators at GABA-A receptors in the brain — producing a calming and sedating effect. This is why evening dosing is typically recommended: it can meaningfully improve sleep quality as a direct pharmacological effect. This mechanism is specific to bioidentical progesterone and does not occur with medroxyprogesterone or norethindrone.
How to track Micronized progesterone
- Sleep quality and latency — the GABA-A neurosteroid effect is one of micronized progesterone's most valued clinical characteristics; tracking sleep quantifies whether it is occurring.
- Dosing time and consistency — taken in the evening, the sedating effect aligns with the sleep window; logging the time you take it reveals whether timing correlates with sleep benefit.
- Mood and emotional stability — GABA-A modulation also affects anxiety and emotional reactivity during the day.
- Side effects: dizziness, next-day grogginess, breast tenderness, bloating.
- Breakthrough bleeding or spotting if on a cyclic regimen — bleeding patterns are diagnostically important and should be logged with dates and description.
- Log the time you use micronized progesterone each evening — the sedating effect is most clinically useful when consistently timed with your sleep window.
- Rate sleep quality on a consistent scale (e.g., 1–10) each morning so you can distinguish the progesterone's contribution from other factors like hot flash reduction.
- Log mood and anxiety as separate entries from sleep — GABA-A modulation affects both, and the patterns are worth distinguishing.
- If you're on a cyclic regimen, log the days you use progesterone alongside any mood or bleeding pattern changes that occur on the off days.
- Note next-day grogginess with the timing of your dose — if it is occurring, adjusting the time of evening dosing may help.
Questions to ask your physician
- My sleep quality log shows [pattern] since starting micronized progesterone — is the sedating effect working as expected, or does that pattern suggest a dose or timing adjustment?
- I've been logging breakthrough bleeding on [dates, description] — what does that pattern indicate?
- My mood tracking shows [pattern] alongside progesterone use — is that consistent with the expected neurosteroid effect at my dose?
- I'm logging next-day grogginess at [frequency] — does that suggest I should take it earlier in the evening, or that my dose may be higher than needed?