The next time you go to the drugstore to pick up shampoo or paper towels, you might get that cough checked out, too.

More than a quarter of the U.S. population lives within a 10-minute drive from a retail walk-in medical clinic (or convenient care clinic) that can provide appointment-free screenings and examinations of minor afflictions right inside the store.

Staffed mostly by nurse practitioners, these clinics offer lower costs and longer hours than a standard physician's office. But how does the quality of treatment at these convenient alternatives compare? Pretty well, according to a pair of studies published online yesterday in Annals of Internal Medicine.

"Retail clinics could serve a relatively large demographic," says lead study author of one of the studies, Ateev Mehrotra, a professor of medicine at the University of Pittsburgh School of Medicine and a researcher at the RAND Corp., a nonpartisan research group. "I had thought of these clinics as being a new issue, a novel way of [providing] care," he says, but after looking into their prevalence, he found that they "could have a substantial impact on the health system."

The first retail clinics opened nearly a decade ago, and as of August 2008, there were nearly 1,000 of these clinics around the country, which had received some three million visits. "The increasing number of patients who receive care at retail clinics has fueled concerns about increased health care costs, greater rates of misdiagnosis, overuse of antibiotics, and decreased delivery of preventative care," the authors in one of the studies wrote.

Many of those concerns may be unfounded, according to the studies, based on patient records from a major insurer in Minnesota, where the clinics first emerged. The quality of care for treating three common acute afflictions—ear infections, sore throats and urinary tract infections—was just as good at retail clinics as at physician offices and urgent care centers, and better than emergency rooms (ERs), when checked against standard clinical treatment guidelines.

The findings about the nurse-only clinics were no surprise to Mehrotra, who cites previous studies showing no difference between care given by physicians as opposed to nurse practitioners.

Nevertheless, Rebecca Patchin, chair of the American Medical Association and an assistant professor of anesthesiology at Loma Linda University School of Medicine in California, recommends that, "store-based clinics have appropriate physician oversight on site and that patients be clearly informed of the qualifications of the person providing care."

Depending on nurses for care, however, is one of the ways retail clinics keep costs down, which can be important for those who seek care there—often young and uninsured folks, Mehrotra says. Most of the clinics take insurance, Medicare and some Medicaid, but out-of-pocket prices are also listed on a service menu, allowing patients to evaluate the cost before treatment. Total costs for treating the three common minor afflictions noted above were on average 30 to 40 percent lower at a retail clinic than at a physician office or urgent care center and 80 percent lower than at ERs.

Sporadic treatment at retail clinics could disrupt continuity of treatment and preventative care, some medical groups worry. But, the study authors found, the number of patients who had preventative care within three months of treatment was about the same across all types of facilities (about 14 percent).

Most clinics are run by for-profit chains such as CVS pharmacies; Walgreens and Target that also have in-store pharmacies, causing Mehrotra and others to worry about medication overprescription. "We actually found, and perhaps surprisingly, retail clinics were not more likely to prescribe," Mehrotra says.

Physician groups caution that the clinics should not become the sole locus of treatment. "Store-based health clinics can offer patients an option for episodic care, but cannot replace the patient–physician relationship," Patchin said in a prepared statement.

How might changes in the health care system and the number of insured individuals alter the use of retail clinics? "It's hard to know," Mehrotra says. He points to anecdotal results from Massachusetts, where more people have gotten insurance, showing that it has become more difficult to get in to see physicians, so a retail clinic model might become increasingly popular.

"From a societal perspective, it might lead to a better allocation of health care resources if more patients with a mild illness go to a retail clinic," the paper authors noted. The American Medical Association, for its part, has yet to issue an unqualified endorsement of retail clinics. As Patchin said in her statement, "Convenience should never compromise safety."