Methods for preparing tannic acid-containing compositions (e.g., pharmaceutical compositions, nutraceutical compositions or medical food compositions), particularly those having enriched tannic acid populations with superior potency, purity and safety profile. Also provide herein are the tannic acid-containing compositions for use in inhibiting D-amino acid oxidase and/or for treating CNS disorder and obesity disorders including diabetes, hyperglycemia, hyperlipidemia or hypercholesterolemia.
