While niacin and niacinamide are both components of vitamin B3 and are often used interchangeably as supplements, there are some critical differences between the two. Niacinamide is the amide derived from niacin, which is also known as nicotinic acid. The two can have different physical effects on the body, and people sensitive to those changes may prefer to use one over the other. They also vary in their usefulness for treating certain conditions such as circulatory problems, high cholesterol, and osteoarthritis.
The most basic difference between niacin and niacinamide is that the second is a derivative of the first. Niacinamide is a type of chemical compound known as an amide, which is defined by a nitrogen atom combined with a carbonyl group, or C=O, which all amides contain. The human body can convert niacin into niacinamide after it is ingested.
Due to a difference in the pharmacological properties of niacin and niacinamide, people can have very different physical reactions when taking one versus the other. Niacin has a distinct vasodilating effect on most people, meaning it will cause their blood vessels to widen when it is taken. This often results in a common side effect, sometimes known as a niacin flush, where the capillaries under the skin open to allow more blood than normal to flow through them and the skin then becomes red, itchy, or even painful for a brief period. Niacinamide does not dilate the blood vessels and therefore does not cause skin flushing, but it may lead to excessive sweating, or hyperhidrosis. Which effect is more likely to be an issue for a person can determine which supplement he or she chooses to take to get adequate amounts of vitamin B3.
Niacin and niacinamide both work equally well when used as a vitamin supplement and can both be used to treat pellagra, or niacin deficiency, but their effectiveness often differs when they are used to treat other conditions. For circulatory issues, niacin is the preferred supplement due to its effects on the blood vessels. It is also well known for its role in lowering high cholesterol levels, preventing hardening of the arteries, and reducing the risk of a heart attack, an effect that niacinamide does not have. Niacinamide, on the other hand, can help treat diabetes and osteoarthritis, whereas niacin is not helpful for these conditions.