Drug makers spent nearly $4.5 billion on television advertising of prescription drugs last year, according to Kantar Media, an ad tracking company.

Even some people who desperately want lower drug prices question how effective the disclosure requirement would be.

David Mitchell, the founder of Patients for Affordable Drugs, a nonprofit advocacy group, said that the disclosure of list prices in TV ads could be helpful to patients, but he added: “We have not seen any evidence that it will lower drug prices. We do not believe drug companies will be shamed by public displays of prices.” Mr. Mitchell has a blood cancer called multiple myeloma.

Carl E. Schmid II, the deputy executive director of the AIDS Institute, a public policy and advocacy organization, said: “The list price is an inflated price and does not represent what the patient pays, nor for that matter, what the pharmaceutical company receives. In and of itself, it is not a useful figure for patients. What they need to know is how much a drug will actually cost them at the time of sale.”

When the Trump administration proposed the price-disclosure requirement last fall, Mr. Azar called it a “historic action” to reduce drug prices by providing consumers with more information.

But in the fine print of the proposed rule, the Department of Health and Human Services made some notable concessions. It acknowledged that “Congress has not explicitly provided H.H.S. with authority to compel the disclosure of list prices to the public.”

In addition, while extolling the benefits of “price transparency,” the department said that “consumers, intimidated and confused by high list prices, may be deterred from contacting their physicians about drugs or medical conditions.” This, in turn, “could discourage patients from using beneficial medications” and “potentially increase” the total cost of care, the department said in a preamble to its proposed rule.