@MikeMason, @simrin-- I've spoken to my doctor about vitex for acne and he told me that it works for some people but doesn't work for others.
He said that vitex is a natural way to increase progesterone levels in the body. If someone is experiencing acne due to a lack of progesterone, then taking vitex will improve it. But if someone has acne despite their hormones being in perfect balance, vitex will do nothing. In fact, it might make acne worse.
Like the article said, some trial and error is necessary to find out if vitex will work. It might also be a good idea to get hormonal testing to find out if there is an imbalance before starting the herb. I think progesterone testing can be done through a simple breath test nowadays.