The present invention relates to a use of grape seed extract or its constituents to treat conditions which benefit from an inhibition of cytochrome P450 2A6 (CYP2A6). In particular conditions which benefit from the inhibition of CYP2A6 are conditions which benefit from decreased metabolism of nicotine to cotinine, for example, preventing, reducing or treating smoking, and conditions which benefit from a decrease in the in vivo formation of carcinogens, for example prevention or treatment of cancer.