My doctor prescribed very high dose niacin years ago for Tryglicerides. They told me to take it at bedtime and I'd sleep
through the side effects. Niacin expands blood vessels and that's a good thing for circulation. High dose Niacin REALLY expands vessels and you get a whole body tingling effect that leaves you feeling like you are sunburned for a half hour to an hour.
It woke me up at 2am every night I took it. I'd go into the family room and turn the ceiling fan on high and sprawl in a chair and let it blow over me. Not fun! After a while it would wear off and I'd go back to sleep.
That said, it's good for circulation and the more blood flowing
through your liver the more the bad stuff is filtered out. Take the highest dose that doesn't cause the above side effects. My doctor says it's harmless, but anyone taking it should read up on the benefits, dosage, and side effects. It's in your daily vitamin tablet in lower doses, anyway.