Emily, I don't have experience with black cohash but I was able to eliminate my hot flashes and improve my sleep with B complex vitamins. I use Superior Source sub-lingual Balance B's. I chose sub lingual to improve the B12 absorption by bypassing the digestive tract. I avoid the women's specific formula because the additional folic acid makes my body too acidic. Taking the B complex after about 2pm has a deleterious affect on my sleep while taking it in the morning helps me sleep better at night.

I've never heard of anyone else using B complex for hot flashes but it could be an inexpensive, simple, and relatively safe experiment for you.