To provide a memantine medication solving the problem of Alzheimer's disease and Parkinson's disease not being fundamentally cured because of unknown causes, and achieving excellent therapeutic effects though the reasons are uncertain.

The causative agents of the diseases are homocystein and homocysteic acid. A metabolism promoter of these causative materials, e.g. pyrrolo-quinoline quinone of a green tea component, and an analogous compound thereof, materials inhibiting the cytotoxicities of the causative materials, and materials inhibiting the production of the causative materials can be therapeutic drugs in addition to the therapeutic agent by an antagonist of the homocysteic acid such as the memantine medication. These fundamental therapies become possible by using them.