A method of treating an amyloid disease, or a disease characterized by alpha-synuclein or NAC fibrillogenesis, in a mammalian subject. The method includes administering to the mammal a therapeutically effective amount of a various disclosed catechins or green tea extract. A pharmaceutical composition comprising a therapeutically effective amount of a catechin and a pharmaceutically acceptable excipient. The therapeutic amount of the catechin or green tea extract is selected for efficacy in treating amyloid, alpha-synuclein or NAC fibrillogenesis in a mammalian subject.