This is from the actual CPhA monograph for Niacin. (Immediate release, not sustained.)
Hepatic: Increased serum aminotransferase concentrations (1–50%): Hepatotoxicity has been reported more frequently with sustained-release formulations. It is usually dose related and reversible (see Warnings and Precautions).
The mechanism by which niacin and niacinamide cause hepatotoxicity is unknown.
That is from compendium of pharmaceuticals and specialties.
The risk is higher when combined with other potentially hepatotoxic drugs like statins...
I don't really get what you want to know - there are a million sources "documenting liver damage from 'actual' (you mean immediate release or non-sustained release formulations) of niacin"... you could go to DRUGS.COM and find it.
Everybody also knows that sustained release formulations produce less liver enzyme elevations and are seen as less hepatotoxic. Sustained release formulations also have fewer other side effects (flushing/headaches) because of the effect on prostacyclin in the body. (You can just take an aspirin with your niacin if those minor side effects bother you).
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what is the actual proof that non-pharmacological niacin is dangerous,
I don't know what "pharmacological" niacin is... you get niacin in your diet everywhere so yeah, there is no proof that it hurts...
if you want to know about high dose niacin therapy... there is evidence...
Likely in the form of case reports which are done at a hospital or doctors office... these have been documented and compiled by the government and manufacturers of these products and this information now appears as warnings in drug monographs
For sustained release: Paopairochanakorn C, White S, Baltarowich L. Hepatotoxicity in acute sustained-release niacin overdose. J Toxicol Clin Toxicol. 2001;39(5):516
For immediate release: Am J Health Syst Pharm. 1997 Dec 15;54(24):2815-9. ASHP Therapeutic Position Statement on the safe use of niacin in the management of dyslipidemias. American Society of Health-System Pharmacists.
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Is there proof that Niacin is actually harmful when it is not the slow release preparation?
Yes there is... but it is really conflicting and may involve older products and the methods by which it was manufactured.
Anything in a large enough dosage can have toxic effects
This is quote from American society of health system pharmacists:
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The frequency of hepatotoxicity appears to be greater
with certain ER products and may be more common
when patients have replaced an IR niacin product with
an ER product at the same dosage. Therefore, patients
should be advised not to change niacin products without
the advice of a qualified health care provider. Some
investigators, however, have found a low frequency of
hepatotoxicity with ER niacin products, suggesting that
all ER niacin products may not be the same. Clearly,
additional research is needed. Because of this increased
risk of hepatotoxicity with ER products, the maximum
dosage recommended by NCEP for this dosage form is 2
g/day.
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in what dosages does therapeutic benefit seize
inafter - seizing benefits lel...
Well, most drugs follow a sigmoidal shapes curve (dose-response curve) and will continue to demonstrate minor benefit with increased dose until say, 100% of all receptors are bound to the drug ... which almost never happens - you'd have to give masssiveeeee dose of most drugs. The thing is, that each additional molecule of drug generates less effect than the previous one did because it may also have to compete for the cells of interest/receptor spot. And at higher doses, it might be so saturating in amount, that it might just start to get into things where it should not, causing problems. So safety and diminishing return of efficacy limit the maximum dose. usually 2grams is max dose where benefits still outweigh risks and other side effects like nausea, flushing, head ache etc. are minor enough. We start the lower and increase with time s they build up tolerance as well.
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It has been used in amounts of up to 30,000mg, and I don't see that documenting liver damage, but I also don't see another similar reference.
If it has been used at 30g daily, that depends on a lot of thing... were the liver enzymes documented or is this just a person who said they felt fine (you don't feel liver toxicity easily), every person is different and many people likely would feel the effects at such a high dose. In the placebo-controlled clinical trials and the long-term extension study, elevations in transaminases did not appear to be related to treatment duration. However, elevations in AST levels did
appear to be dose related. Transaminase elevations were reversible upon discontinuation of NIASPAN (extended release).