It's often cheaper for some Medicare patients to buy prescription drugs through Walmart's $4 generic program than through their own health insurance, according to a study out Monday.
The study's lead author told NBC News it's more evidence that patients can't always rely on health insurance for reasonable prices on their prescriptions.
"Twenty percent of the time, at least, we should go to Walmart," said Dr. Joseph Ross of the Yale School of Medicine.
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The study, published in the Annals of Internal Medicine, was informed by discussion about pharmacy gag rules, Ross said. Those rules prevent pharmacists from telling patients about possible savings on drugs, like by not using health insurance.