At least that brand is actually nicotinic acid. The no-flush kinds have modified formulas and are not recommended to ease POIS.
But yours is a slow release and not a typical no-flush formula, and reduces the possibility of flushing.
To prevent POIS symptoms, a certain quantity of nicotinic acid has to be taken and actively in the bloodstream. Below that quantity it is not very effective.
Near that quantity it is somewhat effective and just over that quantity it is very effective.
The measure of "that quantity" is the flush. For some it may be more and others less, and this will also depend on the quantity of food that has beenn previously ingested. Ideal 3 to 5 hrs of fast is needed to get the flush (or receive the right quantity of niacin in the blood).
So the problem with this slo-niacin, is that it's designed to deliver niacin slowly, with the principal effect of reducing or preventing the flush. And if one were to take enough to produce flush, the flush would likely last an extended period.
Niacin when taken for longer periods seems to develop a threshold, which allows one to take MORE niacin before the flush is felt. So I'm not exactly sure what would happen if enough was taken to produce a flush. Would the body accommodate and be more resistent to the flush.
If it's all you have, then you have to try to make it work. Perhaps you can help us develop a working formula for that kind of niacin.
So the good part is, that it IS pure niacin and not some chemical derivative. The bad news is that it will be difficult to find a dosage that works for you.
I know niacin doesn't work for everyone, but the formula for having it be effective is so precise that I feel there are several among those for whom it doesn't work that have failed just because they aren't following the very strict protocol.