Desensitizing a person to allergies usually involves a series of injections of small amounts of allergens, but a large review of studies has found that putting allergens under the tongue in a water solution might work just as well.
The Food and Drug Administration has not approved sublingual immunotherapy, although it is widely used in Europe, and some American doctors prescribe it off label.
Researchers analyzed 63 randomized controlled trials with 5,131 patients ages 4 to 74. The studies looked at allergies to grass, tree pollen, dust mites, ragweed and other substances.
The review, published in The Journal of the American Medical Assocation, found strong evidence that the oral therapy improves asthma symptoms, with greater than 40 percent improvement compared with placebo, and a significant reduction in the use of asthma medicines. There was moderate evidence that the treatment reduces runny nose and inflammation of the eyes.