The results of in-​vivo studies, in rats, revealed that the use of Quercetin in combination with Indomethacin highly reduced the risk of adverse reaction (gastric ulcerative effect) related to the peroral administration of the drug.  Gross observations and scanning electromicrographs of the mucous membrane and superficial cells of the stomach showed that the Quercetin reduced the damage of mucosal membrane and destruction of the gastric superficial cells presented under the mucous membrane.  The phys. and chem. compatibilities of a double blend of Indomethacin and Quercetin prepd. by solvent evapn. technique were confirmed using IR spectroscopy, differential scanning calorimetry and x-​ray diffractometer.  Also, the results showed that the presence of Quercetin in copptd. mixt. with Indomethacin does not affect the dissoln. characteristics of the drug.  The results suggest that a compatible blend from Indomethacin and Quercetin could be pharmaceutically formulated with the aim of reducing the gastrointestinal adverse effects of Indomethacin.