Niacin is a water-soluble vitamin in the vitamin B class. It is a component of the pyridine nucleotide coenzymes NAD and NADP, and is central in many metabolic redox reactions. It is involved in energy metabolism.
Niacin can be found in whole grains and high protein foods, or it can be manufactured from the amino acid tryptophan (60mg of tryptophan → 1mg of niacin). In its amide form, it is consumed as a supplement. Niacin deficiency causes pellagra.
Nicotinic acid (but not niacinamide) is also a pharmacological role outside of its vitamin role. It is used in gram amounts (aka Niacin flush) to treat hyperlipidemia. It lowers serum cholesterol by inhibiting liver VLDL synthesis, decreasing VLDL, and LDL levels, while often increasing HDL levels significantly. It also increases clearance of VLDL via the lipoprotein lypolysis (LPL) pathway, which contributes to triglyceride reduction.
This drug is useful when combined with statins, or when attacking combined hyperlipidemia where the HDL level is low. Side effects include a harmless cutaneous vasodilation and sensation of warmth after each dose when the drug is started or the dose is increased, though taking aspirin or ibuprofen beforehand blunts this prostaglandin-mediated effect. Pruritus, rashes, and dry skin or mucous membranes may also occur. Niacin is also associated with insulin resistance.