Well, this is based on the incomplete and confusing information I've managed to glean, but...
I've been taking vitex because it's supposed to encourage proper functioning of the reproductive system, and also because it's supposed to reduce PMS breast pain. German scientists think it acts on the pituitary or hypothalamus to regulate hormone production.
I started last May, taking the dried ground herb in capsules. I just took the dosage suggested on the bottle. But then, each time I needed to buy more, I couldn't find the same brand again, and every brand recommended a different dosage!
My midwife researched it, and all the dosage recommendations he felt were reliable referred to the alcohol extract. He told me to take the extract at 40 mg/day. (This is much less than the dosage recommended on that bottle!) I've only been doing that since Feb., so it's hard to say if it's working. I did have less breast pain than usual during my last PMS, but that was a period induced by progesterone suppositories, which are supposed to act locally and not cause so many side effects, so that might be the explanation.
Sorry I can't be of more help! Let us know if you learn anything useful!