Nicotinic acid has been used to lower blood triacyl-glycerol and cholesterol in patients with hyperlipid-emia. However, relatively large amounts are required (of the order of 1–6 g/day, compared with reference intakes of 18–20 mg/day). At this level of intake, nicotinic acid causes dilatation of blood vessels and flushing, with skin irritation, itching, and a burning sensation. This effect wears off after a few days.
High intakes of both nicotinic acid and nicotin-amide, in excess of 500 mg/day, also cause liver damage, and prolonged use can result in liver failure. This is especially a problem with sustained-release preparations of niacin, which permit a high blood level to be maintained for a relatively long time.