An extract from
http://www.aviationmedicine.com/allergies.htm
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Preventive Medication- Nasal Steroids
Another method of prevention is the use of medication to block the body’s reaction the allergens. The most common symptoms of nasal stuffiness are effectively relieved by nasal steroid sprays. These steroids act by stabilizing the cells in the body exposed to allergens so they do not release histamines. They are not immediately effective, but may take several days to weeks to reach their full effect. If someone can anticipate their allergy season, using they agents several weeks before the season starts may block most symptoms. The steroids are usually well tolerated and act on the nose and upper respiratory tract.
They are relatively safe for long term use and the FAA will approve their use if they are effective. Reporting their use to the FAA may be done at the airman’s next physical exam. Some of the name brands for these effective products are
Beconase, Vancenase, Flonase, Nasalide, Nasacort, Nasonex, Nasarel and Rhinocort.