Abstract: Background: Plasma kinins are known for decades but the understanding of them is not up-to the mark and the complexity is the reason. There are many drugs and trials undertaken with these as drug targets but only very few have been successfully marketed and used. Rest all others have resulted in failure during various phases of the trial. Purpose: The purpose of this review is to explain and explore the complexity of plasma kinins and to explore the relations between Kinins and to analyse the failures in drug development with these receptors as targets. Implication: This extensive review might help in understanding the complexity and ensure the reduction of drug development failures in these molecules as drug targets Conclusion: kinins have important role in homeostatic functions of the body physiologically. The pathophysiological roles in inflammation are also known. The complexity of these systems is well established.