Sclerosants administered intravenously as micro-foams, are an established therapy for varicose veins. Rapidly assessing sclerosing agents to determine which are the most effective, and how they interact with normal and dysfunctional vasculature is important. Our microfluidic vein-on-a-chip accurately simulates the physiological conditions of varicose veins in vitro, by combining a human umbilical vein endothelial cell (HUVEC) coated channel with representative flow dynamic and mechanical environments. This allows us to work with University Hospital Southampton NHS and industrial partners at BTG International Ltd, to rapidly determine the therapeutic potential of sclerosing agents. Our future work aims to further enhance physiological accuracy of the vein-on-a-chip by incorporating functional venous valves, and increasing the constituent cell types used to replicate structure and function of the vein wall.