To understand how these deals work, consider the one that the drugmaker Amgen made with Harvard Pilgrim Health Care, a nonprofit insurer in Massachusetts and one of the insurers to most aggressively test the concept. It has entered into at least eight such deals over the past two years. This spring, Amgen agreed to pay a full refund to Harvard Pilgrim if patients who took its pricey new cholesterol drug, Repatha, suffered a heart attack or stroke. Repatha is intended for patients with very high cholesterol levels, for which cheaper drugs, known as statins, do not work.

As part of such deals, insurers eased restrictions on which patients could gain access to the drug, said Dr. Joshua J. Ofman, a senior vice president at Amgen. Sales of Repatha and similar drugs have disappointed in part because insurers have been reluctant to pay for them given their price.

If Harvard Pilgrim patients taking Repatha have a heart attack or stroke, they share in the refund, getting back all out-of-pocket payments that they have made toward the drug, said Dr. Michael Sherman, chief medical officer at Harvard Pilgrim.

Doctors who prescribe Repatha said the deals do not affect how they treat patients. “We’re completely agnostic to it,” said Dr. Frederic S. Resnic, chairman of cardiovascular medicine at the Lahey Hospital & Medical Center in Burlington, Mass., who sees patients with Harvard Pilgrim insurance. The drugs are so costly that doctors still only prescribe them when patients really need them, he said.

Dr. Peter B. Bach, director of the Center for Health Policy and Outcomes at Memorial Sloan Kettering Cancer Center in New York, is skeptical. He said the pharmaceutical industry is conflating setting drug prices based on the value they bring to patients and the health care system, which he supports, with negotiating givebacks when patients don’t respond to drugs, which he sees as too little, too late.

The arrangements, he said, carried “bells and whistles” that made them look good in theory. “But as long as you control all the contract terms, it can be a lot of optics but no substance,” he said.