Dizziness is common side effect of niacin ,niacin also called nicotinic acid ,is a B vitamin (B3) used in vitamin supplement ,use to prevent cardiovascular disease lowering cholesterol and triglycerides in the blood ,it is use for hyperlipoprotenemia and a supplement to treat vitamin B3 deficiency ,some might experience itching under the skin ,redness sweating or chills ,nausea legcramps insomnia