Provided is a method capable of effectively treating various diseases associated with energy excess, such as obesity, diabetes, metabolic syndromes, degenerative diseases and mitochondrial dysfunction-related diseases, via elevation of an NAD(P).sup.+/NAD(P)H ratio by increasing an NAD(P).sup.+ concentration in vivo or in vitro through use of NAD(P)H as a substrate or coenzyme by oxidoreductase such as NAD(P)H:quinone oxidoreductase (NQO1), a method of screening a drug for the same and a therapeutic drug.