Niacin has a wide margin of safety. Toxic effects of nicotinic acid occur only at levels far in excess of requirements. Limited research indicates that nicotinic acid and nicotinamide are toxic at dietary intakes greater than about 350 mg per kg (160 mg per lb) of body weight per day (NRC, 1987). The IV LD50 of niacin in mice is 2.5 g per kg (1.1 g per lb) of body weight. The oral LD50 and subcutaneous LD50 in mice are 4.5 and 2.8 g per kg (2.0 and 1.3 g per lb), respectively. Nicotinamide is two to three times more toxic than the free acid (Waterman, 1978). The nicotinic acid and niacinamide tolerance for ruminants has not been determined.
