While chasteberry is a great herb to use against PCOS, there should be some warnings noted...
If you are on contraceptives for anything, chasteberry will decrease it's effectiveness.
If you are at risk for uterine, breast, or other hormone-dependent diseases and cancers, you should avoid chasteberry as it can exacerbate growth.
If you are on anti-psychotics (Seroquel, Abilify, Thorazine, Compazine, etc.) chasteberry will decrease it's effectiveness and can cause serious chemical interactions.
If you are on dopamine-like drugs (Mirapex, Requip, etc) chasteberry will decrease it's effectiveness and possibly cause serious chemical interactions.
If you are on Reglan chasteberry can cause a decrease in effectiveness and carry negative interaction.
As with all herbs, you should talk to your medical care provider before undergoing any herbal treatment to discuss possible drug interactions.
Just because it's natural doesn't mean it's safe. I wanted to try vitex but couldn't because I was on Seroquel and Reglan... I would've ended up dropping to below safe levels on the Seroquel and would have ended up hurting myself or someone else. Just worth noting.