(CNN) The Trump administration's proposal to require pharmaceutical companies to list drug prices in television ads would have a profound impact on the way consumers think about expensive drugs and whether they would ask their doctor about them, according to a study published Tuesday.

But the study found that the effect was mitigated when the advertisements included modifiers, such as saying the medication might not cost anything due to insurance coverage or other discounts. Pharmaceutical companies have been pushing for such modifiers to be allowed in the ads.

"This regulation has good intentions, but the design of it leaves a huge loophole, and without getting rid of it, this law will have no effect," said study co-author Ge Bai, an expert on health care finance and accounting at Johns Hopkins University. "The loophole is that pharmaceutical companies understand that modifiers work. They will do things to blunt what the administration is trying to achieve."

Health and Human Services Secretary Alex Azar introduced a proposal in October requiring drug manufacturers to include the list price of any drug paid for by Medicare or Medicaid in television ads.

"We will not wait for an industry with so many conflicting and perverse incentives to reform itself," Azar said.

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