Nicotinamide adenine nucleotide (NAD) is a cofactor found in all living cells. It exists in oxidized form (NAD+) and reduced form (NADH). NADH is found widely in nature and is involved in numerous enzymatic reactions in which it serves as an electron carrier by being alternately oxidized (NAD+) and reduced (NADH). NADH supplements are used for improving mental clarity, alertness, concentration, and memory; as well as for treating Alzheimer’s disease and dementia. Because of its role in energy production, NADH is also used for improving athletic performance and treating chronic fatigue syndrome (CFS). Some people use NADH for treating high blood pressure, high cholesterol, jet lag, depression, and Parkinson’s disease; opposing alcohol’s effects on the liver; reducing signs of aging; protecting against the side effects of an AIDS drug called zidovudine (AZT).