The United States has too few doctors, and the Association of American Medical Colleges (AAMC) is projecting that the shortage will grow to more than 90,000 by 2020. The statistics are particularly troublesome for primary care, which accounts for half of the shortage.

Nearly 1 in 5 Americans lacked access to a primary care physician in 2009. That means we have only about half the needed supply for an optimal patient load of 2,500 patients per primary care doctor nationwide. The shortage continues to grow due to several factors, including low reimbursement rates for primary care, lower incomes than for specialty doctors, and high workloads.

Part of the problem is that doctors are retiring faster than students are graduating. They are aging along with the rest of the population, and 250,000 are expected to retire in the next decade. It takes 7 years from the start of medical school until a new doctor can enter practice. That forces many to accumulate a large amount of debt, so they are reluctant to take primary care positions that are lower paying than most specialist slots. Health reform will likely make the shortage worse, because it will add and estimated 32 million more people to health insurance rolls.

Your primary care doctor treats everything from the common cold to diabetes. He or she is the central player in coordinating your care, connecting you with specialists, pharmacists, and others. As the number of doctors per patient decreases, the need to add more of them rises.

Linda Green, a mathematician who studies health care, recently published a study suggesting that the shortage can be avoided if non-physicians take over routine care - treating conditions like strep throats and ear infections. That is where your neighborhood drugstore can help.

On April 4, 2013, Walgreens became the first retail pharmacy chain to add medical services to its traditional role of filling prescriptions. It now offers such services as diagnosing and treating chronic conditions like asthma, diabetes and high cholesterol. To do this, it is using non-physicians - nurse practitioners and physician assistants - at more than 300 Take Care Clinics in 18 states. Where state law permits, they write prescriptions, make diagnoses, refer patients for additional tests, and help people manage their conditions.

While Walgreens has explicitly declared that they are not trying to replace primary care physicians, their entry into the realm of medical care has met with resistance. The president of the American Academy of Family Physicians has warned that its move could harm the quality of care and patient safety. Other medical organizations, such as the American Medical Association, have taken a more pragmatic view of the situation and are in discussions with Walgreens to ensure safety for patients.

Despite the objections, Walgreens has a big advantage. Its costs are projected to be 30% to 40% less than those in doctor's offices, and 80% less than those in emergency rooms. This could position it as a major player in primary care medicine.

While safety concerns remain to be resolved, retail health care is likely here to stay. And it could dramatically change the way we receive health care services.