AZ,
I see slow release niacin as exposing the liver to steady long term exposure to nicotinic acid and whether the niacin is slowly released by a slow dissolving microencapsulation or by the slowly dispersing large inositol-niacin complex, I'm sure the liver perceives the blood's constant delivery of niacin in precisely the same way. I see the same for Niaspan in spite of the company's tortured differentiation between "extended" release, sustained release, long-acting or whatever terms are used.
Nicotinic acid is a weak liver toxin, not unlike statins in that regard, and the toxic effect is enhanced by both doseage and exposure time and the exposure time may be even more important than the dose. People have died from high dose niacin. I read about people who were on a dose of niacin with no problems and switched to the SAME doseage in time release and developed liver damage after the switch.
All that said, after bleary eyed research into the continuing horrors of Lp(a), I am going to double my niacin dosage to 1000 mg. slow release taken once, at night. It's either that or high dose ESTROGEN and I think at my age, a change in secondary sex characteristics would look a bit silly.
Anyone on ANY form of niacin in excess of 500 mg./day should have their liver functions, ALT and AST, checked after the first month and then annually!