Any member of a group of vitamers that belong to the chemical structural class called pyridines that exhibit biological activity against vitamin B3 deficiency. Vitamin B3 deficiency causes a condition known as <a href="https://en.wikipedia.org/wiki/Pellagra" target="_blank">pellagra</a> whose symptoms include depression, dermatitis and diarrhea. The vitamers include nicotinic acid and nicotinamide (and their ionized and salt forms).