If those drugs aren't sufficient or side effects are intolerable, immunotherapy is an option. Researchers are now investigating techniques that may make the therapy more convenient. But for now it still requires progressively larger doses of allergens, such as grass pollen, injected by your doctor into your skin, at least monthly for several years. It also carries a slight risk of anaphylactic shock, requiring patients to remain in the doctor's office for 30 minutes after the shot.

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Leukotriene blockers, such as montelukast (Singulair), zafirlukast (Accolate), and zileuton (Zyflo), are more common for treating asthma but can ease severe nasal allergies. Those drugs are much more expensive than antihistamines and have a higher risk of side effects. Similarly, the injectable drug omalizumab (Xolair) is costly, only officially approved for asthma, and has a high risk of complications, but may be an option for those who have tried everything else.