Numerous compounds acting on the venous system have been developed over the last 50 years, including and often associating flavonoids, pycnogenols, saponosides, nucleosides and bilobatides. Some products have proved highly successful such as Cyclo 3 Fort (Fabroven), Phlebodril, made of ruscus extract (flavonoids, saponins), hesperidin-methyl-chalone and ascorbic acid. This presentation is an attempt to classify the scientifically proven mechanisms of such substances. All selected substances have been tested in clinical trials for their action on the symptoms of chronic venous insufficiency (CVI), leg pain and edema. As the distensibility of the leg veins is the main pathological factor determined by plethysmogaphy, it was at first thought that leg pain would be related to it. But observations have shown that this factor is often unrelated to the enlargement of the veins but rather to a whole chain of factors. The effects of different drugs on venous distensibility, rheological disorders, the prevention of wall dystrophy and action on the microcirculation are examined.