Both Flonase and Nasacort are available without a prescription. These medications contain different steroids but both are meant to treat sinus congestion due to allergies. Neither should be used in children without talking to your doctor first. You can substitute Flonase for Nasocort, but you should use it regularly but shouldn't use more than 1 spray in each nostril twice a day. If you have diabetes, glaucoma, cataracts or liver disease, ask your doctor before using.