Where did you get this info? All I can find is "some doctors speculate high dosages of otc niacin may.."' blah, blah. They go on to say what you really need is the prescription niacin which is perfectly safe. Sounds like the typical big pharma party line. That vitamin might be toxic and really hurt you, UNLESS you use our expensive, prescription formula of it.
Niacin is vitamin B3 and is safe in anything less than massive doses.
It has definitely been proven to lower LDL and raise HDL, and is prescribed by doctors for exactly that purpose. The no flush niacin has been shown to be less effective so you may have to learn to put up with the flushing.
Google it and decide for yourself if the benefits outweigh any possible risks for you.