In biochemistry, flavin adenine dinucleotide (FAD) is the precursor molecule to FADH2. Upon bonding to two hydrogen atoms, FAD is reduced to FADH2 and is turned into an energy-carrying molecule. This is used by organisms to carry out energy requiring processes. FAD, and the more common NAD, are reduced in the citric acid cycle during aerobic respiration.

FAD also stands for Familial Alzheimer disease