Progesterone

• Prepares the uterine lining (endometrium) for implantation.
• Stabilises pregnancy when implantation happens.
• Slows gut motility (bloating and constipation in the luteal phase).
• Acts as a mild anti-mineralocorticoid (competes with aldosterone), prompting a compensatory rise in aldosterone.
• Raises body temperature about 0.3 to 0.5 C after ovulation.
• Has mildly sedating, GABA-like effects in the brain (helps sleep early in the luteal phase).
• Modulates immune function (mildly immune-suppressing in pregnancy).

• Follicular phase (week 1-2 of cycle): low.
• After ovulation: rises sharply.
• Luteal phase (week 3-4): high.
• Late luteal (last 5-7 days): falls if no pregnancy. Drop triggers period and PMS.
• Pregnancy: rises continuously, peaks at 100 to 200 ng/mL late in pregnancy.
• Perimenopause: erratic, often with anovulatory cycles where progesterone barely rises.
• Post-menopause: very low and stable.
• Hormonal contraception (most types): suppresses natural cycle, replaces with synthetic progestin.

Progesterone receptors are widespread in the gastrointestinal tract. High progesterone slows transit by about a day on average. and slows gastric and colonic muscle contraction directly. This is why bloating, constipation, and food sensitivity reactions tend to cluster in the second half of the cycle. They are predictable, not random, and they ease once bleeding is established.

• Short luteal phase (10 days or less) is linked to lower progesterone and a thinner lining, though it has not been proven to independently cause infertility.
• Anovulatory cycles in perimenopause: progesterone never rises, oestrogen unopposed, sometimes very heavy bleeding.
• Diagnosis: blood test on day 21 of a 28-day cycle (timing matters).
• Treatment: bioidentical progesterone (Utrogestan) or synthetic progestins, typically prescribed in perimenopause as part of hormone replacement therapy (HRT), or in fertility care.

Many women in perimenopause find that adding bedtime micronised progesterone, prescribed as part of HRT, improves sleep. The effect is real for some, progesterone metabolises into allopregnanolone, which acts on GABA receptors. Effect varies; some feel groggy, others sleep noticeably better. It is part of standard HRT for women with a uterus and is not yet routinely prescribed for sleep alone.

Bleeding after menopause is never normal hormone fluctuation and needs a doctor urgently, whatever you take. Very heavy or prolonged bleeding (flooding, clots, soaking through protection hourly) deserves prompt review: it is common in perimenopause and treatable. Monthly patterns severe enough to disrupt work or relationships deserve a conversation rather than endurance, and hormone treatment itself, including micronised progesterone, always belongs with a prescriber.