Somewhere in the $40 billion frenzy of healthcare deals announced Thursday, something was bound to falter at some point. But the first crack took barely a day to appear, with U.S. biopharmaceutical firm Medivation (NASDAQ:MDVN) announcing Friday that it had rejected a $9.3 billion takeover offer from French pharmaceutical company Sanofi (NYSE:SNY).

Thursday’s announced mergers and acquisitions drew attention for their sheer combined value. Analysts have attributed those new combinations to tectonic shifts in the healthcare industry, especially as the U.S. government pushes to overhaul the ways doctors and hospitals are paid and to force cumbersome health systems to become more efficient. But companies and investors seem split over whether combining forces is best way for healthcare and drug companies to respond to these sea changes.

Sanofi’s proposal “substantially undervalues Medivation and is not in the best interests of the company and its stockholders,” San Francisco-based Medivation said Friday in rejecting Sanofi's offer.

Sanofi responded that it was “committed to the combination,” which it said “represents a compelling strategic and financial opportunity to drive immediate and certain value for Medivation's shareholders.”

In its unsolicited proposal, Sanofi offered to acquire Medivation for $52.50 per share, which Medivation CEO Dr. David Hung called “substantially inadequate” given the company’s current value and its prospects, saying it had several potential blockbusters in its pipeline. The company also noted that the offer was 21 percent less than Medivation’s 52-week trading high of $66.40. The stock closed at $57.80 Friday.

Other deals also generated uncertainty among investors.

After Abbott Laboratories (NYSE:ABT), headquartered in Lake Bluff, Illinois, announced Thursday it would buy St. Paul, Minnesota-based medical device maker St. Jude Medical (NYSE:STJ) for $25 billion, its shares tumbled to drop Abbott's market cap by more than $5 billion, even though Abbott described the deal as “creating a premier medical device leader with top positions in high-growth cardiovascular markets.”

St. Jude shareholders would receive $85 per share, estimated as being a 37 percent premium over its closing share price Wednesday. (It closed at $76.20 Friday.) Abbott said the St. Jude deal would add 21 cents to its adjusted earnings per share for 2017 and 29 cents the year after.

Some analysts speculate the deal will lead to another spin-off by Abbott, which sold its branded drugs business AbbVie in 2013.

AbbVie (NYSE:ABBV), for its part, also announced a deal Thursday to buy Stemcentrx, a private oncology company, for $5.8 billion in cash and stock.

One reason for so much consolidation, especially within specialty sectors of healthcare and medicine, is that the federal government is trying to push healthcare payments into systems that reward hospitals and doctors for better quality of treatment, not quantity. The way it’s doing that is by changing how it pays them, through a process called bundled payments, where the overall treatment for a medical problem is covered with a single payment, rather than individual payments for every X-ray, every blood test or every checkup issued, known as fee for service.

Under that model, the theory goes, everyone will win. Doctors will be financially motivated to provide the best and most cost-efficient care possible, and patients will ideally be healthier and happier. The rise in healthcare spending, which at $3 trillion a year now accounts for close to a fifth of the U.S.’s GDP, will be curbed.

The list of conditions or medical problems, ranging from bronchitis to urinary tract infections to hip replacements, eligible for these bundled payments from the U.S. government is growing. Meanwhile, doctors and hospitals are under ever greater pressure to cut costs.

In this shifting landscape, pharmaceutical and medical device companies that can lower their prices have a distinct advantage over pricier competitors. Another option, of course, is to gain market share — through strategic purchases of other healthcare companies.