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Allergy Drops - Sublingual Immunotherapy for Allergic Asthma


Updated: July 31, 2008

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What It Is:

Allergy drops are a form of allergic asthma treatment. The more proper medical name is Sublingual Immunotherapy (SLIT). Sublingual means under the tongue, and immunotherapy is a treatment, where small amounts of an allergen are put in to the body in order to reduce sensitivity to it over time.

Allergy drops are similar to injection allergen immunotherapy for asthma, which is also known as allergy shots. But as explained above, with SLIT, the allergen extract is placed under the tongue. SLIT can be in either liquid or tablet form.

Allergy drops have been widely used in Europe for many years but are not yet officially approved for use in the United States by the Food and Drug Administration. In the United States, they are considered to be an alternative treatment for asthma and allergies.

How It Works:

SLIT is meant to stay under the tongue and be partially absorbed into the mucus membranes, where it is dispersed in to the lymph glands that are part of the immune system. Experts are not exactly sure how or why allergy drops work, but studies have shown that there are changes in allergen-specific antibodies. SLIT can be started at a higher maintenance-level dose, which is then used continuously, as opposed to allergy shots that start out with a tiny amount of allergen and are slowly increased to the maintenance level over time.

How You Use It:

Allergy drops or tablets are usually taken daily over a period of years, but there are currently no real standards on how to use allergy drops — even in Europe. After the first dose, which should be given in the doctor's office in case of side effects, you can take allergy drops on your own at home.

That is one of the main reasons why people with asthma and allergies are often interested in allergy drops as an alternative to allergy shots, which must be given by an allergist in the doctor's office, making them potentially more expensive and less convenient.

Safety and Effectiveness:

Allergy drops, as noted above, have been used for many years in Europe, with reportedly beneficial effects. Until recently, though, there has been a significant lack of scientific evidence from controlled studies. By 2005, however, there were 21 studies involving 959 patients that experts could use to analyze the effectiveness of SLIT.

This analysis suggests that SLIT is effective in reducing allergy symptoms. It is difficult to draw specific conclusions, though, as there is great variation in the allergens used as well as how the SLIT is administered and the ways in which researchers measure outcomes. So in 2006, three large well-designed trials were carried out. Unfortunately, the trials only looked at grass pollen allergen immunotherapy, administered in tablet form.

The 1,600 patients involved in the three trials showed a 35 to 40% reduction in symptoms and in the use of rescue medicine during the first year of treatment. Eighty-two percent of the patients receiving the grass pollen tablets reported feeling better, as compared with 55% of those who received a placebo. Since these studies were limited to grass pollen immunotherapy, it is not known how effective SLIT would be against other allergens, though it seems likely similar results could be obtained.

What is not known is whether SLIT could be used effectively with multiple allergens at once. Even with allergy shots, it is not entirely clear whether giving multiple allergens together is completely effective. In addition, there is not enough evidence to know if SLIT continues to be effective once stopped or if the protection is only sustained while actively under treatment.

Side effects with SLIT are usually mild and short-lived. The most common are irritation and itching in the mouth, which generally do not require any change in dose and go away by the eighth day of treatment. Anaphylaxis is quite rare with SLIT.


Allergy drops and tablets are not approved for use in the United States. In Europe, only the grass pollen tablet is officially approved for use, though other SLIT preparations are quite widely available and used. There has been increasing interest in SLIT in the United States recently, so the FDA may decide to approve it at some point if enough clinical trials have validated its effectiveness for treating allergies and allergic asthma.

The biggest stumbling block to approval of SLIT as a treatment is probably the lack of standardization, even in Europe. Although some of the clinical guidelines in Europe do mention SLIT, they do not provide any kind of guidelines for use, so great variation exists in the amount of allergens used, type of allergens and duration of treatment.

In Summary:

If you are interested in exploring allergy drops or tablets for your allergic asthma or nasal allergies, it would be wise to discuss it with a reputable allergist. There may be other types of healthcare professionals who will offer SLIT, but because of the lack of standardization in practice or FDA approval, it may not be beneficial to accept such treatment from anyone but an asthma/allergy specialist who is familiar with your situation.

SLIT is considered quite safe and effective and is more convenient than allergy shots, which (overall) have a stronger record of effectiveness and are usually covered by health insurance — SLIT is not. It should also be noted that even if you do elect to use SLIT, you may still need to use allergy and/or asthma medication, particularly if you are sensitive to multiple allergens.


Frew, Anthony J. MD. "Sublingual Immunotherapy." NEJM. 358:21 2008. <http://content.nejm.org/cgi/content/full/358/21/2259>

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