Hi Na'na!!!
All I can tell you is when I took then together....I really "felt" my ovulations. I have been taking Vitex for 5 months and on the 2'nd month I added Black Cohosh...I did not feel any side effects from it except it put me in BD mood more KWIM
So I was on that combo for two cycles, then stopped because I wanted to try the Vitex with Dong Quai (read that it seemed to work better as a combo to enhance chances for pg).....so that is what I am currently on.
BTW....my "problem" is/was low progesterone....so the Vitex and Black Cohosh definetly seemed to help in my case.
HTH
Rona