In the present study, changes in chemical stabilities were investigated after incubation of commonly-consumed over-the-counter (OTC) drugs with (-)-epigallocatechin-3-gallate (EGCG), a major green tea polyphenol. Stability of EGCG was significantly increased in the presence of millimolar levels of acetylsalicylic acid (Asp); EGCG stability was not affected by ibuprofen and acetaminophen (AAP). Stability of AAP was not altered in the presence of EGCG during 24 hr-incubation at pH 2.0, 7.4, and 8.0. Asp stability and formation of salicylic acid were not affected by EGCG at pH 2.0 either. The present study may provide basic information for chemical interactions between dietary polyphenols and OTC drugs.