The present study evaluates the pharmacodynamic interactions between herb and drugs for anti–inflammatory and analgesic activity. Anti–inflammatory activity of herb Vitex negundo and it’s interactions with Diclofenac sodium and for analgesic activity were studied with Indomethacin. Inflammation was measured with plethysmometer while for analgesic activity by using acetic acid induced writhing test in mice. The further study is performed to evaluate the interactions as such effects of combined drugs for potentiation, additive, antagonistic and synergistic effects. Along with this it also gives information about the effects of combined drugs when taken together. These types of interactions get unnoticed because of this these interactions are clinically significant and also causes serious consequences. Many researcher have a lack of knowledge hence it becomes a part of study.