(A) Experimental protocol for chemopreventive studies of GSE and Res in 4NQO – induced oral tumorigenesis in mice. Animals were randomly divided into four groups: group I (normal AIN-76A diet and tap water), group II (normal AIN-76A diet and 4NQO in drinking water), group III (0.2% GSE w/w in AIN-76A diet and 4NQO in drinking water), and group IV (0.25% Res w/w in AIN-76A diet and 4NQO in drinking water). Mice in group II–IV were given 100 μg/mL of 4NQO in drinking water for 16 consecutive weeks. After 8 weeks of 4NQO exposure, mice in group III–IV were given GSE or Res in diet as indicated in ‘Materials and methods’ for 8 weeks while continued on 4NQO administration. Effect of GSE and Res on (B) body weight, (C) water consumption and (D) diet consumption. *, P<0.001; NS, not significant; GSE, grape seed extract; Res, resveratrol.