I take Niacin, for cholesterol (I think it's supposed to raise good cholesterol, if I remember correctly). It's a B-vitamin (B-9 I think). My doctor recommended I take it at night, because sometimes it can make you feel warm, or sweaty, and if you take it before bedtime, you sleep right through it. I did notice at first, waking up a couple times, with the back of my neck reallly hot and sweaty, but that only happened a couple times in the first month or two.
I used to take chromium (fell for the hype), but stopped when my doctor told me that it doesn't do much if you're not diabetic. If you're diabetic, it supposedly helps regulate your blood sugar better. They caution diabetics not to take it without talking to their doctor though if they are already taking insulin or other blood sugar regulating medications, as you could end up with low blood sugar, if you don't adjust your doses of the other meds.