Excessive neurogenesis from supplements almost always lead to things to like glioblastomas, or brain cancer more simply put. You should always be wary of anything related to increased growth or cell division.
That's why I mentioned you should always be wary of anything that purports to increase neurogenesis, as even if it does, that can lead to significantly increased probabilities of cancer development. And brain cancer specifically, is one of if not the most difficult types of cancer to treat, with extremely limited survival outlooks.