NADH stands for "nicotinamide adenine dinucleotide (NAD) + hydrogen (H)". It is a coenzyme that is central to metabolism and is found in all living cells. NADH is a key molecule in the process of glycolysis, which is the breakdown of glucose to produce energy. It is involved in making energy in the body and is important in both catabolism and anabolism. NADH is also used in anabolic reactions, such as gluconeogenesis. The balance between the oxidized and reduced forms of NADH is called the NAD+/NADH ratio, which is an important component of the redox state of a cell. The effects of the NAD+/NADH ratio are complex, controlling the activity of several key enzymes.

NADH is also used as a supplement for various conditions, such as chronic fatigue syndrome, high blood pressure, high cholesterol, athletic performance, depression, and Parkinsons disease. However, there is no good scientific evidence to support these uses. NADH supplements might affect blood pressure and have other effects. When taken by mouth, NADH is possibly safe for most people when used for up to 12 weeks.

In summary, NADH is a coenzyme that is central to metabolism and is involved in making energy in the body. It is also used as a supplement for various conditions, but there is no good scientific evidence to support these uses.