Caglayan E, Axmann S, Hellmich M, Moinzadeh P, Rosenkranz S. Vardenafil for the treatment of raynaud phenomenon: a randomized, double-blind, placebo-controlled crossover study. Arch Intern Med. 2012 Aug 13;172(15):1182–4. doi: 10.1001/archinternmed.2012.2271. PMID: 22710940.