If allergies to grass pollen, ragweed, or dust mites are making you sneeze, drip, and itch, you might want to know about a newer preventive therapy: sublingual immunotherapy, or SLIT.

According to the American College of Asthma, Allergy, and Immunology, the prescription treatment offers an alternative to traditional immunotherapy—commonly called allergy shots or subcutaneous immunotherapy (SCIT) in medical lingo. But instead of injections, you place a tablet under your tongue.

With allergy shots, a doctor injects you with increasingly larger amounts of allergens over time, gradually increasing your tolerance to them. This can take three to five years.

Sublingual immunotherapy involves holding a dissolvable tablet containing purified extracts of the offending allergens under your tongue for a few minutes a day.

SLIT has been used in Europe and some other areas for decades. But here, the treatment is approved by the Food and Drug Administration (FDA) only for certain grass pollens, ragweed, and, more recently, dust mites. Studies on sublingual immunotherapy for other allergens are underway.

If you're looking for more allergy relief, here's what you need to know about SLIT.

How SLIT Works

An allergist will initially administer the treatment in his or her office to ensure that you don't experience significant side effects such as anaphylaxis, a potentially deadly allergic reaction.

After that, you should be able to take the tablets yourself at home. (Allergy shots are always given under medical supervision.)

Currently, four FDA-approved SLIT treatments are available. The newest, which became available in mid-January, is Odactra, the first approved for house dust mite allergies, a year-round problem for millions of Americans. The others are Oralair, for five different grass pollens; Grastek, for Timothy grass allergies; and Ragwitek, for ragweed allergies.

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All are only for those age 65 and younger. Depending on the specific SLIT treatment, younger people may start at age 5 (for Grastek), 10 (Oralair), or 18 (Odactra and Ragwitek).

Some doctors prescribe sublingual drops instead of tablets and recommend them for a wider range of allergens, including cat dander. But that approach is still being studied and is "off-label"—legal, but not for a use that's officially approved by the FDA.

For grass and ragweed, it's wise to begin treatment three to four months before the allergy season gets underway, says Mark S. Dykewicz, M.D., the Raymond and Alberta Slavin Endowed Professor in Allergy & Immunology at the Saint Louis University School of Medicine. 

This way, by the time grass and ragweed are in full bloom, you'll have built up a tolerance to the allergens and your reactions to them should be significantly diminished. (Ragweed season tends to be late summer to early fall; grass pollen is prevalent in late spring, or in warmer areas, all year.)

For dust mite allergies, according to The Medical Letter, a nonprofit periodical for healthcare providers, it can take up to 14 weeks of Odactra use for symptoms to ease. Clinical trials have found that it reduced allergy symptoms and the need for allergy medication by 16 to 18 percent compared with a placebo. 

SLIT may cause mild side effects such as itchy or irritated mouth and throat, and nausea or abdominal discomfort. Severe reactions such as anaphylaxis appear to be quite rare.

However, guidelines released by the American Academy of Allergy, Asthma, and Immunology and the American College of Allergy, Asthma, and Immunology recommend that people using SLIT have a prescription for an epinephrine auto-injector—and know how to use it—just in case.

Is SLIT for You?

You might consider the under-the-tongue approach if you have frequent, bothersome dust mite, grass, or ragweed allergy symptoms that don't respond sufficiently to allergy medications such as steroid nasal sprays, and you don’t want to use traditional immunotherapy.

But what's a better choice, tablets or shots? Some early research suggests that SLIT may be "somewhat less effective" than allergy shots, according to UpToDate, which provides evidence-based treatment information to healthcare providers. Experts say that clinical trials comparing traditional immunotherapy with sublingual are needed to determine which is more helpful. 

In addition, notes Dykewicz, "patients who are allergic to multiple allergens would be better candidates for SCIT, which can be used to treat multiple allergens. Administration of several different types of SLIT tablets together has not been well-studied."

And while the risk of a serious allergic reaction with SLIT is far lower than it is with allergy shots (which is why the injections are always given in a medical setting), the sublingual approach isn't for everyone, he adds.

For example, you shouldn't use it if you have conditions such as severe, unstable, or uncontrolled asthma; eosinophilic esophagitis (EOE), an immune disorder that can make swallowing food difficult; or a history of a severe reaction to immunotherapy. If you're considering the therapy, be sure your doctor has your full medical history.