Oxymetazoline HCl. Nasal decongestant. Fast acting 12 hour relief. Fast, effective relief of: sinus pressure; nasal congestion. The medicine in Sudafed OM Sinus Congestion temporarily relieves nasal congestion and sinus pressure, helping to restore freer breathing through the nose. It works by shrinking swollen nasal membranes, helping to clear your nasal passages.