High Quality Content by WIKIPEDIA articles! Riociguat (BAY 63-2521) is a novel drug that is currently in clinical development by Bayer. It is a stimulator of soluble guanylate cyclase (sGC). At the moment Phase III clinical trials investigate the use of riociguat as a new approach to treat two forms of pulmonary hypertension (PH): chronic thromboembolic pulmonary hypertension (CTEPH) and pulmonary arterial hypertension (PAH). Riociguat constitutes the first drug of a novel class of sGC stimulators.