Hormones are chemical messengers
A hormone is a molecule made in one part of the body that travels through the bloodstream to change what another part is doing. The four that run the menstrual cycle come from two places: the pituitary gland (FSH, LH) and the ovaries (estrogen, progesterone).
Think of the pituitary as a manager sending instructions. FSH says 'grow follicles.' LH says 'release the egg.' The ovaries then report back with estrogen and progesterone, which change what the uterus, brain, breasts, skin, and gut are all doing.
The four hormones
- FSH — Follicle Stimulating Hormone
- Made by the pituitary. Rises at the start of each cycle and tells the ovaries to start ripening follicles. Very high FSH after age 45 is a signal of perimenopause.
- Estrogen (mainly estradiol)
- Made by the growing follicles. Builds the endometrial lining, sharpens cognition, raises energy, thins cervical mucus. Peaks just before ovulation.
- LH — Luteinising Hormone
- Made by the pituitary. Surges around day 12–14 and triggers ovulation. This is what over-the-counter ovulation kits detect in urine.
- Progesterone
- Made by the corpus luteum after ovulation. Stabilises the endometrium, raises basal body temperature, calms the nervous system. If pregnancy doesn't happen, it drops and you bleed.
Why symptoms shift across the cycle
Rising estrogen in the follicular phase is why many people feel sharper, more sociable, more up-for-it in the week after their period. It's not a coincidence — estrogen enhances serotonin and dopamine signalling.
Progesterone in the luteal phase is calming for some and destabilising for others. In people with PMDD, the brain seems to respond abnormally to normal progesterone fluctuations — this is the current leading theory.