The era of giant pharmacy managers that brokered prices between drug companies and insurers and employers has been upended, now that the $69 billion merger between CVS Health and Aetna, a big health insurer, has been approved by the Justice Department.

The merger can go ahead as long as Aetna sells off its private Medicare drug plans, the Justice Department said in announcing the deal’s approvalon Wednesday.

CVS Health was the last of the large independent pharmacy managers to enter into deals with major insurers, consolidating control over the money that Americans spend on medical care and prescription drugs.

The deal is the latest in a flurry of combinations among health care companies in the past few years. Last month, the Justice Department approved Cigna’s takeover of Express Scripts, a major CVS rival.

The companies involved say that they will be better able to coordinate care for consumers as the mergers help tighten cost controls. But critics worry that consumers could end up with far fewer choices and potentially higher expenses.

“This type of consolidation in a market already dominated by a few, powerful players presents the very real possibility of reduced competition that harms consumer choice and quality,” George Slover, senior policy counsel for Consumers Union, an advocacy group, said in a statement.

The organization had opposed the merger, arguing that people enrolled in Aetna health plans could be forced to seek care at CVS retail clinics, and that those who were not insured by Aetna could pay higher prices for drugs than those who were.

“The combination of CVS and Aetna creates an enormous market force that we haven’t seen before,” Mr. Slover said.

The country’s three largest pharmacy benefit managers, or P.B.M.s, have wielded tremendous power for decades, negotiating with drug companies over the prices of brand and generic drugs, and acting as go-betweens for employers and insurers.

Amid a growing outcry over the high price of medicines, pharmacy managers have been vilified alongside big drug makers. Critics point to pharmacy managers’ secretive deals — under which price-setting strategies are not publicly disclosed — that they say enrich companies on all sides of the prescription drug pipeline while failing to benefit consumers.

In addition to the two major entities now attached to powerful health insurance companies, OptumRx, another major pharmacy manager, is owned by UnitedHealth Group, the parent of the large insurer. Anthem, which operates for-profit Blue Cross plans in several states, is developing its own in-house pharmacy operation.

“There are going to be mammoth organizations,” said Adam J. Fein, the chief executive of Drug Channels Institute, a research firm.

The role of pharmacy benefit managers has changed over time. Generic drugs now account for about 90 percent of all prescriptions, and higher drug prices are largely a product of the increase in expensive specialty medicines for conditions like rheumatoid arthritis or cancer.

“The job of the P.B.M. is being transformed,” Mr. Fein said.

Facing the prospect of competition from outsiders like Amazon, whose tentative forays into the pharmacy business have already shaken up the industry, established players have also been looking for ways to stay relevant to their customers and enlarge their share of the health care market.

The companies “are feeling pressure to do something different or it will be done to them,” said Brian Marcotte, the chief executive of the National Business Group on Health, which represents large employers.

Some employers are actively looking for alternatives to the status quo. This year, Amazon, JPMorgan Chase and Berkshire Hathaway announced plans to form a new company to address the high costs and frustrations that their employees must contend with as they navigate the existing system.

“It’s a disruptive period of time when the players are rearranging themselves,” said David W. Johnson, the chief executive of 4sight Health, a consultant.

Although the Justice Department appears willing to allow so-called vertical mergers by companies that do not directly compete, Aetna said last month that it would sell its private Medicare drug plans to WellCare Health Plans to address concerns that the combined companies would control too much of the market.

State regulators and consumer groups have also raised concerns about the impact of the Aetna’s merger with CVS, saying that the lack of large pharmacy managers that aren’t affiliated with insurers could make it difficult for smaller competitors in either sector.

Previous mergers in the industryhave left consumers with fewer choices and higher drug bills, said David A. Balto, an antitrust lawyer who is a critic of the pharmacy managers.

“This is a marketplace that hasn’t done well because of lack of transparency, and transparency may be even weaker,” said Mr. Balto, who had worked at the Federal Trade Commission and the Justice Department. Affiliations with large insurers could also change that dynamic, he added. “It might correct some of the more pernicious practices.”

Mr. Balto warned that while state officials have not traditionally overseen pharmacy managers, the combined mammoths “could bring them into the cross hairs of regulation.”

The mergers also show how far organizations are crossing the traditional line between insurance companies responsible for paying for care and providers responsible for delivering it.

There have always been organizations that perform both functions, but the lines have become increasingly blurred. UnitedHealth, for example, has been aggressively buying physician practices and surgery centers, while Humana announced plans to become the nation’s largest provider of hospice care.

“The nature of the last six to 12 months is much more vertical and the size of the deals are significantly larger,” said Gurpreet Singh, a partner specializing in health care services at the consulting and advisory firm PwC.

Much of the enthusiasm over CVS’s acquisition of Aetna has focused on the insurer’s addition of a retail component and the potential for to it to use CVS’s 10,000 pharmacies and 1,100 retail clinics to deliver care, particularly to Aetna customers.

Imagine a single hub where someone can go to get care for everything from a sore throat to their diabetes.

“In our new health care model, we provide people access to more affordable care when, where and how they need it,” Larry Merlo, CVS’s chief executive, recently said. “Care will be coordinated among the health care providers, caregivers and their health care teams, leveraging the connectivity CVS will provide.”

Mr. Merlo will be the chief executive of the combined companies, and Mark T. Bertolini, Aetna’s chief executive, will step down and join the CVS board. CVS has committed to keeping Aetna at its headquarters in Hartford for the next decade.

CVS stores could become places to get blood tests for monitoring chronic conditions, not just toothpaste or prescription refills. “You could see the store as a base of operations for a lot of these delivery channels,” said George Hill, a senior analyst at RBC Capital Markets.

Mr. Hill said CVS was also well situated for any onslaught by newcomers like Amazon. In addition to the regulatory hurdles such entrants would have to scale to sell prescription drugs, people typically buy medicine from drugstore or mail-order companies dictated by their health plan.

“You’re going to go where your payer has told you to go,” Mr. Hill said.

It may be years before it is clear whether Aetna and CVS can succeed in changing how their businesses operate.

“There’s a lot of opportunity,” Mr. Marcotte said, but warned that the size of the combined companies makes it even more challenging. “These big mergers take a while to integrate,” he said.

Source: The New York Times