If allergies to grass pollen or ragweed 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. 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 Saint Louis University School of Medicine.

Ragweed season tends to be late summer to early fall, while grass pollen is prevalent in late spring, or in warmer areas, all year round. 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.

SLIT has been used in Europe and some other areas for decades. But here, this treatment is only approved by the Food and Drug Administration (FDA) for a few allergens. (Odactra, the first SLIT for dust mite allergens, was approved in March, but there's no release date for it yet, and studies on sublingual immunotherapy for other allergens are underway.)

Here's what you need to know about SLIT.

How SLIT Works

With SLIT, 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 tablet yourself at home (allergy shots are always given under medical supervision).

Currently, three FDA-approved SLIT treatments are available: Oralair, for five different grass pollens; Grastek, for Timothy grass allergies; and Ragwitek, for ragweed allergies.  

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 (Ragwitek).

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

Mild side effects such as itchy or irritated mouth and throat and nausea or abdominal discomfort may affect three-quarters of users, but often subside within a week or two, according to UpToDate, which provides evidence-based treatment information to healthcare providers.

Severe reactions are quite rare. However, recent 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 grass or ragweed allergy symptoms that don't respond sufficiently to antihistamines and steroid nasal sprays, and don’t want to use traditional immunotherapy.

"The ideal patient for grass and ragweed SLIT tablets would be someone who is not getting adequate relief of seasonal rhinitis, restricted to the grass or ragweed season, using medications," says Dykewicz.

But should you choose shots or tablets? Experts say that clinical trials comparing traditional immunotherapy with sublingual are needed to determine which is more helpful. Some early research suggests that SLIT may be "somewhat less effective" than allergy shots, according to UpToDate.

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 is not for everyone, explains Dykewicz.

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