Answer: Nicotinic acid induces insulin resistance and hence causes glucose intolerance. But this is not the reason for diabetics being intolerant to nicotinic acid. The most important reason for intolerance to nicotinic acid irrespective of whether one is diabetic or not is its non glycemic side effects which include flushing, itching and hepatotoxicity. Crystalline nicotinic acid has lesser incidence of glycemic effects but has more itching, flushing and hepatotoxicity.
Flushing may be reduced if one takes Aspirin about 30 minutes before the Niacin dose.