All About Sublingual Immunotherapy

Allergy Drops Under the Tongue

Allergy Drops
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What is Sublingual Immunotherapy?

Sublingual immunotherapy, or SLIT, is a form of immunotherapy that involves putting drops of allergen extracts under the tongue. Many people refer to this process as “allergy drops,” and it is an alternative treatment for allergy shots. This form of immunotherapy has been used for years in Europe, and recently has had increased interest in the United States. However, it is not approved by the Food and Drug Administration (FDA) in the United States.

SLIT is usually delivered one of two ways: drops (or tablets) of allergen extract are placed under the tongue, then either swallowed or spat out. Most studies have looked at swallowing the extract, which seems to work better. Immunotherapy by the oral route (swallowed and not kept under the tongue for any period of time), causes too many gastrointestinal side effects (nausea, vomiting, diarrhea), and therefore is not used.

Generally, SLIT is administered daily, or multiple times per week, over a period of years. Most patients are able to self-administer SLIT at home. Studies have looked at giving SLIT before a pollen season, during a pollen season, both, or year-round. It is not yet known what the best dosing regimen is for SLIT.

How Does SLIT Work?

The immune system of the gastrointestinal tract tends to "tolerate" foreign substances, meaning that it does not respond in an over-active way to swallowed material.

This makes sense; otherwise the body would over-react to anything swallowed, including food. When SLIT is administered into the gastrointestinal tract, the immune system tolerates the allergen, instead of the over-reactivity of the immune system, as with allergic disease. This results in less allergy symptoms when the body is exposed to the allergy source, such as airborne pollen or pet dander.

How Well Does SLIT Work?

SLIT appears to be effective in the treatment of allergic rhinitis, allergic conjunctivitis and, to a lesser degree, allergic asthma. While most studies on SLIT do show benefit in the treatment of allergic disease, the results are somewhat inconsistent, with up to one-third of studies showing no benefit over placebo treatment.

What is the Safety of SLIT?

Over the past 10 years, the safety of SLIT has been well documented. Serious and fatal reactions to SLIT have not been reported to date. Mild side effects, such as an itchy mouth, occur in the majority of people, and moderate side effects have been documented (1 in about every 12,000 doses), including:

  • lip, mouth and tongue irritation
  • eye itching, redness and swelling
  • nausea, vomiting, abdominal cramping and diarrhea
  • sneezing, nasal itching and congestion
  • asthma symptoms
  • urticaria and angioedema

Because of the safety of SLIT, people generally treat themselves at home, and are followed in the clinic at close intervals to monitor response to treatment.

Who Could (or Should) Receive SLIT?

People with documented allergic disease (allergic rhinitis, allergic conjunctivitis and/or allergic asthma) by allergy testing may be considered for SLIT.

Young children have been shown to tolerate and benefit from SLIT, as have older adults. Pregnant women, as is considered the general rule of thumb for allergy shots, can continue SLIT during pregnancy, but should not start the therapy while pregnant. People with severe asthma may need to be monitored more closely on SLIT, since asthma symptoms can worsen with SLIT.

Most studies on SLIT have focused on people with one type of allergy, such as grass or dust mite allergy. People with multiple allergies, such as to molds, pollens, pet dander and dust mite may not be good candidates for SLIT, given the large volume of different allergen extracts that would need to be taken.

Is there any form of SLIT that has received FDA Approval?

In 2014, the FDA has approved three SLIT products for the treatment of seasonal allergic rhino conjunctivitis. All three exist as an oral disintegrating tablet that is placed and held under the tongue. These products include Grazax (for grass allergy), Oralair (for grass allergy) and Ragwitek (for ragweed allergy). Unfortunately, these products will only be effective for symptoms caused by grass and/or ragweed allergy, and not by other allergens.

Why are Other Forms of SLIT Not Yet FDA Approved?

Multiple studies are currently being conducted for the purpose of trying to get SLIT approved in the United States, but is it likely that approval is at least a few years away. Until the FDA approves the use of SLIT, most mainstream allergists will not offer this type of therapy, and insurance companies will not cover the costs of the therapy. Some health-care professionals are offering SLIT, but people should use extreme caution and talk with a reputable allergist before choosing this non-FDA approved treatment.

Questions that remain to be answered prior to SLIT receiving FDA approval:

  • What is the effective dose, dosing regimen and timing of SLIT?
  • How can multiple allergens be given in an effective, convenient and cost-effective way?
  • Is SLIT safe for high-risk groups?
  • What is the significance of the known side effects?

How Does SLIT Compare with Traditional Allergy Shots?

Traditional allergy shots are a proven therapy in treating allergic rhinitis, allergic conjunctivitis, allergic asthma and venom allergy for nearly a century.

Allergy shots have been FDA proved for many years, although they need to be given in a physician’s office due to the potential for severe side effects. Therefore, they may be an inconvenience to many people.

Studies comparing the efficacy of traditional allergy shots and SLIT show that allergy shots are better at treating allergic rhinitis and asthma symptoms.

In addition, immunologic markers and other tests that correlate with response to immunotherapy are seen less commonly in people receiving SLIT. Therefore, while allergy shots appear to be superior at treating allergic disease, SLIT will likely become an important treatment option for people unwilling or unable to receive allergy shots.

Want to keep learning? Read more about traditional allergy shots.


Cox LS, Linnemann DL, Nolte H, Weldon D, Finegold I, Nelson HS. Sublingual Immunotherapy: A Comprehensive Review. J Allergy Clin Immunol. 2006;117:1021-35.

Potter PC. Update on Sublingual Immunotherapy. Ann Allergy Asthma Immunol. 2006;96:S22-5.

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