Yep. The real question is whether higher HDL levels are per. se. protective against arteriosclerosis or if higher HDLs are simply a sign of something else that's protective - and if it's the latter, whether niacin is raising HDL without changing the risk factor.

There have been some studies that don't show lowered CVD events with niacin - but those were niacin in addition to as much statin as the patient could tolerate (standard of care) - so the jury's still out.

On top of that, the liver, when presented with a 'surge' of niacin, needs to store it by converting it to NR or get rid of it via methylation. Storage is limited, so unless taken as NR it's mostly methylated - and that methylation has a cost in methyl donors.

Speaking of surge, the liver has two pathways for converting niacin to NR, a fast one, and a slow one. The slow one has byproducts you don't want. Both operate in tandem, but avoiding extended release means the slow pathway has limited time to operate.

OTOH, niacin used to be the only treatment available so there's plenty of usage data indicating that it's not harmful.

Not a doctor, just had to figure this out for myself by digging through research papers and clinical studies.

TL;DR: It's... complicated.