When we examine a normal, healthy monthly cycle, we find that
estrogen is the dominant hormone from menstruation to ovulation.
Then,
in response to ovulation, estrogen levels fall, progesterone levels
quickly rise and assume dominance during the final two weeks prior to
menstruation.
If during this two week period if there
is a surplus of estrogen, a lack of progesterone or a blockade of
progesterone receptors, Estrogen Dominance results and is most often
followed by many of the unpleasant symptoms of PMS.
Diet, stress and xenoestrogens
(foreign oestrogens), often introduced in the form of contraceptives,
are all major contributors to this disorder.
The most marked changes usually occur
the week before the onset of menstruation, but milder symptoms may
occur at the time of ovulation. 
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