Riociguat (Adempas(®)), a soluble guanylate cyclase stimulator, is a new, 
first-in-class drug approved for the treatment of patients with chronic 
thromboembolic pulmonary hypertension (CTEPH) [inoperable or 
persistent/recurrent following surgery] or pulmonary arterial hypertension 
(PAH). It has been designated an orphan medicine by the European Medicines 
Agency and the US FDA. This article reviews the available pharmacological 
properties of oral riociguat and its clinical efficacy and tolerability in 
adults with CTEPH or PAH. Riociguat is effective and well tolerated in patients 
with inoperable CTEPH or persistent/recurrent CTEPH following pulmonary 
endarterectomy, and in patients with PAH. It has a positive result on exercise 
capacity and pulmonary haemodynamics, and improves WHO functional class. Most 
adverse events can be attributed to the vasodilatory mechanism of riociguat; 
however, there is a potential for serious bleeding and fetal harm, and riociguat 
use is contraindicated in pregnant patients. Pulmonary endarterectomy remains 
the first treatment of choice for CTEPH, as it is potentially curative. 
Head-to-head trials comparing riociguat with the approved phosphodiesterase type 
5 inhibitors in patients with PAH would be of value for the placement of 
riociguat in the management of this disease. Riociguat is a promising addition 
to the treatment options for patients with CTEPH or PAH.