Researchers have developed the first drug that can protect the 1.5 million Americans who are allergic to peanuts — the leading cause of all allergy deaths.

The monthly shots are not a cure. But doctors believe the still-experimental drug should let people avoid severe complications if they unknowingly eat one or two peanuts, the typical accidental exposure.

“Basically, we would not be seeing people in the emergency room or the morgue from peanut accidents,” said Dr. S. Allan Bock, an allergist from Boulder, Colo., who was not part of the study.

However, the drug is a few years away from going on the market. Its critical third round of tests has been stalled by legal infighting among the three companies with rights to it.

And Dr. Hugh A. Sampson of Mount Sinai Medical School in New York said patients would need lifelong monthly shots of the drug, called TNX-901, and still would have to guard against eating peanuts.

Peanut allergies account for 50 to 100 deaths in the United States each year. Some youngsters must eat at a peanut-free cafeteria table or even in an isolated room. Some airlines have stopped serving peanuts to safeguard people allergic to even a whiff of the nut.

Peanut allergies have been rising in recent decades. No one is sure why, but a new study found that baby creams or lotions containing peanut oil may lead to peanut allergies.

Babies whose rashes or eczema were soothed by such creams were more likely to become allergic to peanuts than those whose creams did not include peanut oil, said Dr. Gideon Lack of St. Mary’s Hospital at Imperial College in London.

Lack’s study — and research on the effectiveness of the allergy drug — were presented Monday in Denver to the American Academy of Allergy, Asthma and Immunology. They will be published Thursday in the New England Journal of Medicine, which released them Monday on its Web site.

The drug is likely to be expensive, but none of the companies involved would say what it may cost.