For the past decade and a half, people suffering from minor maladies such as earaches and sore throats have flocked to a low-cost, convenient place for treatment — clinics inside drugstores and department stores.

But a study published Monday suggests such convenience may come at a cost: Researchers found that retail clinics — Massachusetts has 58 — increase medical spending by attracting people who otherwise would have stayed home.

“So many people have emphasized that retail clinics are a way to save the health care system money. That may not be the case,’’ said Dr. Ateev Mehrotra, a Harvard Medical School professor and an author of the study, published in the March issue of the journal Health Affairs.

Proponents have argued that retail clinics substitute for more expensive visits to doctor offices, urgent care centers, and hospital emergency departments. That’s true some of the time, the researchers found. More often, they said, the clinics merely substituted for doing nothing, thus adding costs to the health care system.

The extra cost is modest — estimated at only $14 a year for each patient who uses the clinics. But use of retail clinics is growing, said Mehrotra, who is also an adjunct researcher at the RAND Corp., a nonprofit that does research to inform public policy.

Several specialists who read the study said it left questions unanswered.

“What we don’t know from this study is what are the impacts on health,’’ said Dr. Elliott S. Fisher, director of the Dartmouth Institute for Health Policy and Clinical Practice. “Is this utilization a good thing or a bad thing?’’

For example, he said, the study doesn’t analyze whether the fast, early treatment prevented problems that might have led to costlier care later on.

But Mehrotra said the conditions measured rarely lead to serious problems.

The retail clinic industry’s trade group, the Convenient Care Association, denounced the study as outdated and inaccurate, saying researchers overlooked the retail clinics’ role in providing access to those who wouldn’t otherwise be able to get care. Other research, the association said, has shown retail clinics reduce overall health care costs.

Dr. Andrew J. Sussman, president of MinuteClinic — the CVS-owned company that runs the largest number of retail clinics nationwide — said about half of MinuteClinic patients have no other source of care.

“We want to be able to provide patients with timely care so it doesn’t get worse,’’ and more expensive to treat, he said. “There’s a profound shortage of primary care physicians. Retail clinics can help keep patients healthy.’’

Retail clinics are staffed by nurse practitioners or physician assistants who treat a limited menu of ailments, such as urinary tract infections and sinusitis. In recent years, they have begun expanding into managing chronic diseases such as diabetes, and offering preventive services such as smoking cessation, although those services were not part of the study. The clinics are open evenings and weekends, require little or no waiting, and have a good record of providing appropriate care, usually at lower cost than a physician.

Introduced in 2000, retail clinics now number more than 2,000 nationwide, receiving more than 6 million patient visits annually. Massachusetts health authorities first allowed the clinics in 2008, after an intense argument about whether they would disrupt patients’ relationships with their primary care doctors. All of Massachusetts’ retail clinics are MinuteClinics run by CVS.

Researchers from Harvard, RAND, and other institutions examined the insurance claims of 13.3 million Aetna enrollees in 22 cities from 2010 through 2012. (None of the clinics in the study was in New England, where retail clinics are relatively new.) They identified 500,000 people who sought care at retail clinics for 11 conditions, including urinary tract infections, influenza, allergies, and ear infections. Then, they compared these people with a similar group who did not go to a retail clinic.

The two groups of patients had similar characteristics before some visited retail clinics, so researchers could assume that roughly the same number of, say, sore throats would occur in each group. But when they looked at the claims, the group that used retail clinics was significantly more likely to have sought treatment for their sore throats than the other patients.

Researchers estimated that 42 percent of the time, patients who used retail clinics went there instead of visiting a doctor, urgent care center, or hospital emergency room. But the rest — 58 percent of clinic visits — represented use of medical care that wouldn’t have happened if the patient had not gone to a retail clinic. These additional visits led to a 21 percent increase in spending for these minor conditions.

Mehrotra said the findings might prompt insurance plans to reconsider incentives, such as waiving copayments, that encourage use of retail clinics. The research also raises questions about whether a similar increase in costs is occurring at physician offices that are extending their hours to increase access. There are similar cost questions about new technologies, such as programs that enable patients to consult doctors over the Internet.

Dr. Nitin S. Damle, president-elect of the American College of Physicians and chairman of its study group on retail clinics, said retail clinics “have a limited role to play.’’ Damle said a few of his patients visit a MinuteClinic a quarter mile from his office in Wakefield, R.I. Many then come to see him for follow-up or to confirm the clinic did the right thing — a duplication that may also add costs.

“They do provide a service that may be of value to patients who have minor acute problems and who are relatively healthy,’’ he said. “Beyond that, they really don’t provide a valued service.’’

The popularity of retail clinics is part of a trend toward greater access that will only grow with the advent of telemedicine, said Dr. Steven Strongwater, president of Atrius Health, an alliance of Eastern Massachusetts medical groups. Atrius has long offered evening and weekend hours, but Strongwater said he sees no risk that extra access will lead to unnecessary visits. Unlike at retail clinics, he said, a visit to a doctor can provide added value, such as identifying unrelated problems, missed vaccinations, or other gaps in care.

Dr. G. Alan Kurose, president of Coastal Medical, a Rhode Island group practice that stays open evenings, weekends, and holidays, said the study “challenged assumptions in an important way.’’ But until more is known, he’s not going to back off from Coastal’s efforts to expand access.

“Convenience matters to the patient,’’ he said. “Expectations are changing and the behaviors of consumers of health care are changing. There’s no going back to the old way.’’

Felice J. Freyer can be reached at felice.freyer@globe.com. Follow her on Twitter @felicejfreyer.