That 2% slice of the rebate cash flow now gives drug manufacturers and other PBM critics a tool they can use to attack PBMs and confuse the public about why U.S. prescription drugs cost so much, Witty said.

"We're taking that excuse off the table," Witty said.

UnitedHealth does not post details about the cash flow related to drug debates, but it reported in its annual financial statement filing for 2023 that it accumulated $11 billion in prescription rebate receivables on its consolidated balance sheets as of the end of 2023, up from $8.2 billion at the end of 2022.

The backdrop: PBMs help employer-sponsored health plans, unions, insurers and other payers set up prescription drug benefits programs and buy the drugs needed to run the programs. The big PBMs operated by UnitedHealth, Cigna and CVS Health have come under relentless attacks in Congress, state legislatures and elsewhere in recent years.

Critics have accused PBMs of pushing up drugs' retail prices to maximize rebates and increase PBM revenue that's based on the total value of the rebates and other discounts negotiated.

Mark Cuban, a former "Shark Tank" investor and the founder of the Mark Cuban Cost Plus Drug Co. mail-order pharmacy, has argued that most of the rebates at employer-sponsored plans come from what employees pay for cost-sharing and put unfair burdens on the plan participants.

Pharmaceutical Research and Manufacturers of America, a trade group for drug manufacturers, is running television ads featuring a PBM "Middleman" villain who snatches a rebate card away from a bewildered patient.

Republicans and Democrats on the House Energy and Commerce Committee are trying to revive a group of popular, bipartisan health insurance bills that expired in December, when the 118th Congress ended and representatives of President-elect Donald Trump blocked an effort to put the bills in the legislation that ultimately created the American Relief Act 2025 anti-government-shutdown and hurricane-disaster-aid package. One of the bills that could be revived would forbid PBMs from keeping any of the prescription drug rebates they negotiate for employer-sponsored health plans.

Some small and midsize PBMs emphasize that they already pass all rebates on to the customers or provide clear reporting to help customers understand where the benefits of the rebates are going.

Related: 5 ways to improve your PBM procurement process in 2024

Witty accused drug manufacturers and other prescription drug market players of attacking Optum Rx and other PBMs to try to weaken one of the few forces holding down what payers pay for drugs.

"Pharmaceutical prices in America are high," Witty said. "The PBM acts on behalf of the ultimate payer. That is often lost."

One sign that Optum Rx is serving the ultimate payers well is that Optum Rx had a 98% customer retention rate in 2024 and attracted 750 new customers that provide prescription benefits for 1.6 million people, Witty said.

Earnings: UnitedHealth held the conference call to go over earnings for the fourth quarter of 2024, which ended Dec. 31.

The Minnetonka, Minnesota-based health insurer and health care services company reported $5.8 billion in net income for the latest quarter on $101 billion in revenue, compared with $5.7 billion in net income on $94 billion in revenue for the fourth quarter of 2023.

The UnitedHealthcare health insurance unit generated $3 billion in operating earnings on $74 billion in revenue, compared with $3.1 billion in operating earnings on $71 billion in revenue for the year-earlier quarter.

UnitedHealthcare ended 2024 providing or administering major medical coverage for 51 million people, down from 53 million people at the end of 2023.

The number of people who had fully insured individual or group coverage from UnitedHealthcare increased to 8.8 million, from 8.1 million.

The number of participants in the employer-sponsored self-insured plans that the company administered increased to 21 million, from 19 million.

Company executives noted during the conference call that health claim costs were higher than what executives had hoped they'd be at the beginning of the year but that claims for the fourth quarter were in line with what the company saw in the third quarter.

Earnings were lower than securities analysts had predicted, and investors responded by pushing the price of a share of UnitedHealth stock down about 4% when compared with the previous day's close, to about $517 per share as of noon today, and pushing the prices of the shares of Cigna, CVS Health, Elevance and Humana down about 2%.