List of products in the National Drug Code with proprietary name . Niacin (nicotinic acid) is used to prevent and treat niacin deficiency (pellagra). Niacin deficiency may result from certain medical conditions (such as alcohol abuse, malabsorption syndrome, Hartnup disease), poor diet, or long-term use of certain medications (such as isoniazid). Niacin deficiency can cause diarrhea, confusion (dementia), tongue redness/swelling, and peeling red skin. Niacin is also known as vitamin B3, one of the B-complex vitamins. Vitamins help to support the body's ability to make and break down natural compounds (metabolism) needed for good health. Niacinamide (nicotinamide) is a different form of vitamin B3 and does not work the same as niacin. Do not substitute unless directed by your doctor. Check the ingredients on the label even if you have used the product before. The manufacturer may have changed the ingredients. Also, products with similar names may contain different ingredients meant for different purposes. Taking the wrong product could harm you.