Large doses of niacin can result in clinical and laboratory findings that may necessitate discontinuation. Adverse effects usually reverse on discontinuation of high doses.


A high daily dose of niacin (nicotinin acid) is around 3 grams per day.


Clinical findings:

(1) vasodilatation and flushing (secondary to histamine release and reduced by premedication with aspirin)

(2) pruritis or urticaria

(3) blistering and hyperpigmentation of the skin

(4) nausea and vomiting, stomach ache

(5) headache

(6) diarrhea or constipation

(7) cardiac arrhythmias


Laboratory findings:

(1) decreased triglycerides

(2) increased HDL cholesterol

(3) elevation of liver function tests (transaminases, alkaline phosphatase)

(4) elevated serum uric acid levels

(5) hyperglycemia in diabetics (secondary to insulin resistance)


High doses should be avoided or used with caution in patients with:

(1) unstable angina

(2) predisposition to gout

(3) diabetes mellitus

(4) liver disease


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