Objectives: Riociguat is approved for pulmonary arterial hypertension and has antiproliferative, anti-inflammatory and antifibrotic effects in animal models of tissue fibrosis. We evaluated the efficacy and safety of riociguat in patients with early diffuse cutaneous systemic sclerosis (dcSSc) at high risk of skin fibrosis progression., Methods: In this randomised, double-blind, placebo-controlled, phase IIb trial, adults with dcSSc of <18 months' duration and a modified Rodnan skin score (mRSS) 10-22 units received riociguat 0.5 mg to 2.5 mg orally three times daily (n=60) or placebo (n=61). The primary endpoint was change in mRSS from baseline to week 52., Results: At week 52, change from baseline in mRSS units was -2.09±5.66 (n=57) with riociguat and -0.77±8.24 (n=52) with placebo (difference of least squares means -2.34 (95% CI -4.99 to 0.30; p=0.08)). In patients with interstitial lung disease, forced vital capacity declined by 2.7% with riociguat and 7.6% with placebo. At week 14, average Raynaud's condition score had improved ≥50% in 19 (41.3%)/46 patients with riociguat and 13 (26.0%)/50 patients with placebo. Safety assessments showed no new signals with riociguat and no treatment-related deaths., Conclusions: Riociguat did not significantly benefit mRSS versus placebo at the predefined p<0.05. Secondary and exploratory analyses showed potential efficacy signals that should be tested in further trials. Riociguat was well tolerated., Competing Interests: Competing interests: DK reports personal fees from Actelion, grants and personal fees from Bayer AG, grants and personal fees from BMS, grants from Pfizer, personal fees from Arena, personal fees from Eclos Sciences, Inc, personal fees from BI, personal fees from Arena, personal fees from CSL Behring, personal fees from GSK, personal fees from Galapagos, personal fees from Genentech/Roche, personal fees from Corbus, personal fees from Cytori, grants from Horizon, outside the submitted work. OD reports other from Actelion, other from Bayer, other from Boehringer Ingelheim, other from Mitsubishi Tanabe, other from AnaMar, other from ChemonAb, other from espeRare Foundation, other from Genentech/Roche, other from GSK, other from Inventiva, other from Italfarmaco, other from iQvia, other from Lilly, other from Medac, other from MedImmune, other from Pharmacyclics, other from Novartis, other from Pfizer, other from Sanofi, other from Serodapharm, other from UCB, other from Amgen, other from AbbVie, other from Mepha, other from MSD, outside the submitted work. YA reports personal fees from Actelion, personal fees from Bayer AG, grants and personal fees from BMS, grants from Inventiva, personal fees from BI, grants from Roche, grants from Sanofi, outside the submitted work. CPD reports personal fees from Actelion, personal fees from Bayer AG, grants and personal fees from Inventiva, personal fees from BI, personal fees from Roche-Genentech, personal fees from Sanofi Aventis, grants and personal fees from CSL Behring, grants and personal fees from GlaxoSmithKline, outside the submitted work. MK reports grants and personal fees from Actelion, personal fees from Bayer AG, personal fees from Chugai, personal fees from BI, personal fees from Reata, personal fees from Corpus, personal fees from CSL Behring, personal fees from GlaxoSmithKline, personal fees from Mochida, personal fees from Pfizer, personal fees from Nippon Shinyaku, outside the submitted work. MMC reports grants and personal fees from Actelion, grants from Chemomab, grants and personal fees from BMS, grants from Pfizer, grants and personal fees from MSD, grants from Sanipedia, personal fees from Janssen, outside the submitted work. JEP reports personal fees from Actelion, personal fees from Bayer AG, personal fees from BMS, personal fees from AbbVie, personal fees from Lilly, personal fees from Roche, personal fees from Sanofi, personal fees from Merck, personal fees from Novartis, personal fees from Pfizer, personal fees from Sandoz, personal fees from UCB, personal fees from Amgen, outside the submitted work. TA reports grants and personal fees from Astellas, grants and personal fees from Takeda, grants and personal fees from Mitsubishi Tanabe, grants and personal fees from Chugai, grants and personal fees from Daiichi-Sankyo, grants from Otuska, grants from Takeda, grants and personal fees from Pfizer, grants from Alexion, grants from Bayer, grants from Eisai, grants from Bristol-Myers Squibb, grants from Asahi Kasei, personal fees from Ono, personal fees from Sanofi, personal fees from Eli Lilly, outside the submitted work. LC reports personal fees from Actelion, personal fees from Bayer AG, personal fees from BI, personal fees from Roche-Genentech, personal fees from Lilly, personal fees from Medac, personal fees from Novartis, personal fees from Pfizer, outside the submitted work. EH reports grants, personal fees and non-financial support from Actelion, grants, personal fees and non-financial support from Bayer AG, grants, personal fees and non-financial support from GlaxoSmithKline, grants, personal fees and non-financial support from MSD, grants and personal fees from Pfizer, outside the submitted work. TI reports personal fees from Astellas, personal fees from Daiichi-Sankyo, personal fees from Chugai, personal fees from Sanofi, personal fees from AbbVie, personal fees from Bristol-Myers, personal fees from Mitsubishi Tanabe, personal fees from Eisai, personal fees from Janssen, personal fees from Asahi Kasei, personal fees from Ono Pharmaceutical, personal fees from Ayumi Pharmaceutical, personal fees from Pfizer, outside the submitted work. Virginia Steen reports participation in advisory boards, consultancy for economics of scleroderma management, and clinical trials for Bayer; investigator-initiated grant, advisory board, and steering committee (consulting) for CSL Behring; advisory board and site primary investigator (PI) of clinical trial for Roche; site PI of clinical trial for Sanofi; site PI of clinical trial for Immune Tolerance Network; and DSMB for open labs phase 2 trial and site PI for the phase 3 trial for Corbus. ME-T reports consulting fees, speaking fees and honoraria from AbbVie, BMS, Lilly, Medac, MSD, Pfizer, Roche, UCB, outside the submitted work. MW reports employment from Bayer AG, outside the submitted work. KL reports other from StatFinn Oy, outside the submitted work. JdOP reports other from Bayer AG, outside the submitted work. ZY reports other from Bayer HealthCare, outside the submitted work. FK reports other from Bayer AG, outside the submitted work., (© Author(s) (or their employer(s)) 2020. Re-use permitted under CC BY. Published by BMJ.)