Question: What is the difference between niacin and niacinamide?

Niacin and niacinamide are both forms of vitamin B-3, and they can be used interchangeably in daily doses of 100 mg or less. However, each form has specific health applications when used in higher doses. Niacin is often taken to support cholesterol levels already within the healthy range (both LDL and HDL), while niacinamide is used to help promote a healthy insulin response, as well as to help maintain joint health. A third form of vitamin B-3 known as inositol hexaniacinate is similar to niacin, but it does not produce the red, prickly flush that often accompanies the latter form, and for this reason it is commonly referred to as flush free niacin.

tl;dr: Niacin is used for support for healthy cholesterol levels already within the normal range. Niacinamide is used for support for joint comfort, support for sugar balance and support for brain function, but does not support cholesterol balance.