For decades, allergy sufferers in Europe and much of South America have been able to control their allergies with daily under-the-tongue drops instead of shots.

And while the prescription drops are not yet approved by the Food and Drug Administration, their use is spreading across the U.S.

Last month, Dr. Todd Zachs, a West Hartford, Conn., ear, nose and throat specialist, began offering the drops to his patients.

Like shots, the active ingredients in the drops are customized to the patients' allergies and use the same allergy antigens. Because the antigens in the shots are FDA-approved, it is legal for doctors to prescribe the medication in a novel way. In this practice, known as off-label prescribing, a doctor uses an approved drug in a way that is not specifically listed in the FDA package insert. Botox and blood pressure medications prescribed for migraine headaches are common examples of off-label use.

Zachs said he became interested in the drops after some insurance companies started charging his patients a co-payment for each weekly allergy shot. The co-payments of $10 to $25 a week became such a burden that some patients stopped taking the shots.

Like shots, said Zachs, allergy drops are not for people who just sneeze for two weeks when the trees bud each spring. They are for people whose immune systems overreact to a variety of environmental offenders, mistaking harmless dust, pollen or other substances for threatening bacteria and going into overdrive to repel them.

Allergy drops work in the same way that shots do. The idea is to inoculate people with small amounts of the substances they are allergic to so their bodies gradually develop immunity. Because such small amounts of the allergens are introduced with each shot or drop, it can take three to five years to reach a point at which a patient allergic to pollen, for example, will not sneeze in the spring.

Instead of going to a doctor's office for weekly shots, patients can take allergy drops at home. Patients place one or two drops under the tongue first thing in the morning and before going to bed at night. There is no taste and the only reported side-effect can be some itching under the tongue for the first several weeks of treatment.

The drops cost about $12 a week, with most patients buying a three-month supply. They are not covered by most health insurance plans.

It is estimated that several hundred doctors in the United States are using allergy drops without the FDA's blessing, and their decision remains somewhat controversial.

Dr. Linda Cox, an allergist in West Palm Beach, Fla., says she is not prescribing allergy drops. Cox is co-chairman of a joint task force of the American College of Allergy, Asthma and Immunology and the American Academy of Allergy, Asthma and Immunology that is researching allergy drops.

In its most recent report, the task force refused to endorse the drops because a review of 100 studies published in English, French and German did not specify exactly what dose of the drops should be given for maximum usefulness.

“We need to know how much works,” Cox says, noting that the dose for a twice-daily drop would not be the same as a dose for a weekly shot.

Several studies in the United States are expected to answer that question, possibly within a year. The largest study is being done by Greer Pharmaceuticals of South Carolina, a company that makes the antigens now used in allergy shots. Cox says she would like to see another study done by a university or physician group independent of the allergy industry. But so far none has heeded the call.

And while she is wary of the drops, largely because they are not approved and not covered by insurance, Cox says she expects to have them in her office sometime in the future.

“It's gaining such ground it's hard to completely ignore it,” Cox says. “It's just expensive to introduce something in the U.S. market.”