Lipoic acid-d 4 ((R)-(+)-α-Lipoic acid-d 4 ) is deuterium labeled Lipoic acid. Lipoic acid ((R)-(+)-α-Lipoic acid) is an antioxidant, which is an essential cofactor of mitochondrial enzyme complexes. (R)-(+)-α-Lipoic acid is more effective than racemic Lipoic acid.