If your sleep gets worse the week before your period, or you've started waking at 2–4am with no obvious reason, progesterone is usually the first place to look.
What progesterone does for sleep
Progesterone's metabolite allopregnanolone activates GABA receptors — the same calming pathway benzodiazepines hit. Adequate progesterone supports sleep onset and continuity. Falling progesterone (perimenopause, luteal phase, postpartum) takes that calming signal away.
When to test
Progesterone needs cycle-day timing — day 21 of a 28-day cycle, or 7 days post-ovulation. Drawn on day 3, it's almost always low and tells you nothing. Drawn on the wrong day in perimenopause, you can miss the diagnosis.
What else affects luteal sleep
Cortisol (the inverse of progesterone for sleep), blood-sugar volatility overnight, thyroid drift, and magnesium status. Progesterone is the lead but rarely the whole story.