Hormones and the cycle

Progesterone

Also called: the cycle hormone, luteal hormone

Progesterone is a sex hormone produced mainly by the corpus luteum in the second half of the menstrual cycle and by the placenta in pregnancy. It prepares the uterine lining for pregnancy, stabilises mood, supports sleep, and slows gut motility. Levels drop sharply if pregnancy does not happen, triggering a period and many of the PMS symptoms women feel in the last week of their cycle.

What progesterone does in the body

  • Prepares the uterine lining (endometrium) for implantation.
  • Stabilises pregnancy when implantation happens.
  • Slows gut motility (bloating and constipation in the luteal phase).
  • Increases water retention via aldosterone activation.
  • 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).

When and how it changes

  • 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.

How progesterone affects the gut

Progesterone receptors are widespread in the gastrointestinal tract. High progesterone slows transit by about a day on average, increases intestinal permeability slightly, and amplifies visceral sensitivity. 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 within 1 to 2 days of bleeding starting.

Low progesterone, when it matters

  • Short luteal phase (under 10 days) can affect fertility because the uterine lining does not have time to mature.
  • 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 HRT, or in fertility care.

Progesterone for sleep

Many women in perimenopause find that adding bedtime progesterone (Utrogestan 100 to 200 mg) 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.

Common questions

Why am I more bloated after ovulation?
Rising progesterone slows gut motility and increases water retention. Bloating builds in the late luteal phase, but objective fluid measurements show retention actually peaks on day 1 of bleeding, then resolves within 24-48 hours. It is hormonal, predictable, and not a food problem.
Can I take progesterone for sleep?
Yes if you are perimenopausal or post-menopausal and have a uterus. Bedtime Utrogestan 100 to 200 mg is part of standard HRT and many women find sleep improves. Not a recreational sleep aid; needs prescriber oversight.
Is progesterone the same as progestin?
No. Progesterone is the body's natural hormone (also available as bioidentical Utrogestan). Progestins are synthetic versions used in some contraception and older HRT. Effects overlap but are not identical.
Does progesterone cause weight gain?
Mostly not. The luteal-phase weight increase most women see is water retention (1 to 3 kg), which clears within 2 days of bleeding. Long-term progestin contraception is associated with mild weight gain in some users; bioidentical progesterone is generally weight-neutral.

Sources