Apigenin
Flavonoid found in yarrow, parsley, chamomile and celery. It has progesterone-like and anti-oestrogenic properties, as well as a mild anxiolytic activity via GABA-A receptors. It is one of the documented active compounds explaining the use of yarrow in the second half of the cycle.
Never use a dietary supplement without the advice of a healthcare professional. Overdoses as well as deficiencies are not without risk.