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Sublingual Immunotherapy (SLIT)

What is Sublingual Immunotherapy and how does it work?

Sublingual immunotherapy, or SLIT, is a form of immunotherapy that involves putting drops or dissolvable tablets of allergen extracts under the tongue. They are then either swallowed or spat out. Studies suggest that keeping the allergen under the tongue then swallowing the extract seems to work better.

The immune system of the gastrointestinal tract tends to tolerate foreign substances, ie it doesn’t overreact to swallowed material. This makes sense because otherwise the body would overreact to anything swallowed, including food.

So with SLIT, the immune system tolerates the airborne pollen, pet dander or other allergen and becomes desensitised, resulting in fewer allergy symptoms when the body is exposed to it.

The process is often referred to as “allergy drops” and is an alternative treatment for allergy injections. Although SLIT has been used for years in Europe this form of immunotherapy is not approved by the Food and Drug Administration (FDA) in the United States.

In the UK GPs may prescribe sublingual immunotherapy for severe cases of allergic rhinitis (hayfever). The tablets are made up of Timothy grass pollen extract and go by the brand name Grazax. You may find a private doctor more willing to prescribe this treatment than an NHS GP as the tablets are expensive and have to be taken for 3 years.

Sublingual immunotherapy using Grazax is usually administered daily, or several times per week and after the first dose has been administered by a doctor 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.

If you would like to read more about Grazax, please click here.

How Well Does SLIT Work?

Most studies on sublingual immunotherapy show benefit in the treatment of allergic disease and it appears to be effective in the treatment of allergic rhinitis, allergic conjunctivitis and allergic asthma. However, the results are somewhat inconsistent, with up to one-third of studies showing no benefit over placebo treatment.

How safe is Sublingual Immunotherapy?

Over the past 10 years, the safety of SLIT has been well documented with no serious or fatal reactions having been reported. 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 diarrhoea
  • 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 Can Receive SLIT?

  • People who have been diagnosed with a positive skin prick test and/or specific IgE test to an allergen may be considered for SLIT.
  • Children over the age of five have been shown to tolerate and benefit from SLIT, as have older adults.
  • Pregnant women can continue SLIT during pregnancy, but should not begin the therapy while pregnant
  • People with severe asthma may need to be monitored more closely, since asthma symptoms can worsen with SLIT.

Most studies on desensitisation using SLIT have focused on people with one type of allergy, such as grass or dustmite allergy. Those with multiple allergies, such as to moulds, pollens, pet dander and dust mite may not be good candidates for SLIT because of the number of different allergen extracts that would need to be taken.

Recommended Home Allergy Tests 

You can test yourself for allergy to pollen, cat and dustmite at home, with an economical 3-in-one finger prick test that will give the same IgE results as the tests carried out in hospitals.


More allergy info and advice here