Drug synergy must be taken into account when prescribing several drugs for treating the same disorder. Synergies are sometimes known from clinical trials, but they are not systematically studied. In this paper, we present a visual approach for identifying and explaining the potential synergies between the 2–15 drugs available for a given disorder. It is based on the chaining of two bioinformatics databases, Drug Bank and Signor, and relies on set visualization with rainbow boxes. We apply this approach to antihypertensive drugs, and show that some European recommendations can be visually deduced and explained.