Safety and Tolerability Differences Between Nicotinic Acid and Nicotinamide

Chemical Identity

Nicotinamide (also called niacinamide) is chemically identical to the amide form of vitamin B3; the two names refer to the same molecule. 1, 2
Niacin (nicotinic acid) is a distinct form of vitamin B3 with different pharmacologic properties. 1, 2

Flushing of the face, arms, and chest typically appears within 30 minutes after oral intake of nicotinic acid. 3
Transient hypotensive episodes can occur, especially in older adults, at doses as low as 30 mg/day. 1, 2
High‑dose nicotinic acid (≈ 3 g/day) is associated with hepatotoxicity ranging from mild liver‑enzyme elevation to acute liver failure. 3
The tolerable upper intake limit for free nicotinic acid is set at 10 mg/day. 1, 2

Nicotinamide does not cause flushing, making it better tolerated than nicotinic acid. 1, 2
The tolerable upper intake limit for nicotinamide is 12.5 mg/kg/day (approximately 900 mg/day for an adult). 1, 2
No adverse effects have been observed in prolonged studies of patients with diabetes at doses up to 25 mg/kg/day. 1, 2
The European Society for Clinical Nutrition and Metabolism (ESPEN) guidelines state that typical dietary intakes of nicotinamide present no safety concerns. 3

Both nicotinic acid and nicotinamide serve as precursors to NAD⁺ and can be interconverted within the body. 1, 2