The purpose of the present invention is to provide a lactic acid dehydrogenase inhibitor with mild side effects on humans that can be used as an active ingredient in cancer therapeutic drugs and metabolic disease therapeutic drugs, and to provide a pharmaceutical preparation using this inhibitor. The present invention provides a lactic acid dehydrogenase (LDH) inhibitor containing a compound expressed by formula (I) (where in the formula, either R1 or R2 represents hydrogen and the other represents a hydroxyl group, or both together represent oxygen bonded to a carbon atom by a double bond), particularly a compound expressed by formula (II) (stiripentol)； and also provides an anticancer agent and metabolic disease therapeutic drug containing this lactic acid dehydrogenase inhibitor as an active ingredient.
