Antihistamines and decongestants are standard for treating allergies, but they're not the only game in town. New drugs on the market and in development target different molecular mechanisms in the production of allergy symptoms.
Decongestants constrict blood vessels in the nose, shrinking nasal tissues. Antihistamines block the receptors for histamine, reducing production of mucus. Other molecules important in the allergic response include leukotrienes, IgE, and phosphodiesterase-4. Three new classes of allergy drugs are based on research into the role of these molecules.
Leukotriene receptor antagonists. Montelukast (brand name Singulair) is already approved for allergies as well as asthma. This is a once-a-day pill. A recent medical article reports that it improves quality of life for most patients, either alone or in combination with antihistamines. Side effects include gastrointestinal symptoms, fatigue, fever, stuffy nose, cough, flu, upper respiratory infection, dizziness, headache, and rash.
Anti-IgE antibodies. Omalizumab (brand name Xolair) is a recombinant humanized monoclonal antibody which binds to the immunoglobulin E (IgE) molecules which play a key role in allergic reactions. This injectable biologic drug is approved in the United States for treatment of allergic asthma. It is currently in clinical trials for seasonal allergies, peanut allergy, milk allergy, cat dander allergy, allergic rhinitis, atopic dermatitis, and urticaria (skin rash). A Japanese study demonstrated that omalizumab is effective in treating seasonal allergies to Japanese cedar pollen. Side effects include injection site reactions, viral infections, upper respiratory tract infection, sinusitis, headache, sore throat, and rare cases of anaphylaxis. The cancer rate was slightly elevated for patients receiving omalizumab in clinical trials: 0.5 percent for the drug, compared to 0.2 percent for placebo.
Phosphodiesterase-4 (PDE4) inhibitors. This is a more speculative approach to allergies. I found one clinical trial in progress for roflumilast (brand name Daxas) for allergies.