These offices maintain publicly accessible Web sites on current prescription drug prices at the pharmacies in their respective states. The researchers confirmed the prices by direct contact with the pharmacies.
For some drugs, the price differences between pharmacies were dramatic.
Consider metformin, one of the most popular diabetes drugs in the United States and the 10th most popular generic drug prescribed overall in 2008, with 40 million prescriptions written, according to Drug Topics magazine.
According to the new study, a 30-day supply of metformin sold for $4.00 in the generic drug discount program at Wal-Mart and Target and for $5.00 at Kmart. But the local neighborhood pharmacies averaged $38.95 and pharmacy chain Rite Aid charged $39.99.
While stores such as Wal-Mart have heavily marketed their low-cost generic programs, they tended to offer more competitive prices for non-generic drugs as well, the researchers found.
And, although the superstores and mail-order pharmacies did not consistently offer lower prices for every medication, none of the local chains or independently-owned pharmacies had the lowest price for any drug on the list.
When prices for the 10 drugs most commonly prescribed to diabetes patients were added (excluding rosiglitazone), the monthly totals were:
$428.35 for Medco by Mail (excluding shipping and handling)
$432.53 for Wal-Mart
$483.94 for Kmart
$501.65 for Drugstore.com (excluding shipping and handling)
$505.95 for Target
$584.44 for CVS
$633.11 for Duane Reade
$638.31 for Walgreen's
$639.20 for local pharmacies
$641.90 for Rite Aid
Unfortunately, this kind of price information is not readily available in most states, said Dr. Patricia Coon of the Billings Clinic in Billings, Mont.
Nevertheless, savvy patients and physicians can find this information locally by doing their homework, said Coon, who was not involved in the study.
"They do a lot of shopping from pharmacy to pharmacy to get the lowest price," Coon said. "It's not unusual for patients to be asking to be switched to generics or the generic that's offered by a Wal-Mart or large brand."
Jackness agreed, noting that even if it is not posted in a central location, price information is available with a phone call.
"People shouldn't assume a drug is the same price everywhere," he said.
In his own New York City practice, Jackness said he often recommends low-priced local outlets to patients at financial risk.
"If we see patients without insurance we tell them to go down to Penn Station and go to Kmart," he said.
But realizing the savings from purchasing all medications at a superstore or mail-order company may not be possible for all patients, the researchers noted.
"The patient must have the physical ability and means of transportation to travel to these stores or order online," they said.
They cautioned that the study did not take into consideration insurance coverage, which might limit how much its findings can be generalized.
But regardless of patients' insurance status, the findings should serve as a wakeup call for physicians to take an active role in ensuring patients are able to obtain their prescribed medications, Jackness and Tamler concluded.
If adherence is an issue, physicians should ask patients about the impact of medication costs and suggest cost-lowering strategies, Robertson said.