When Pfizer announced plans to acquire Allergan for $160 billion, the first questions to surface had to do with the feasibility of the deal. What are the tax implications? What would a combined Pfizer-Allergan look like? 

The deal not only creates the world’s largest drugmaker but also one of the world’s largest advertisers. Combined Pfizer and Allergan spent a total of $1.6 billion on advertising in 2014, according to Kantar Media.  

At stake are the fates of the drugmakers’ massive brand budgets for drugs like Viagra, Celebrex, Botox and Juvederm, to name a few. There remains a lot of uncertainty about which agencies will be left outside looking in and which firms will be awarded potentially hundreds of millions of dollars in new billings when the dust clears, according to agency executives interviewed for this story.

An unnamed executive at an independent healthcare agency said the merger will likely lead to a consolidation of marketing agencies. “It’s not a matter of if, but when,” he said. “They have to figure out how profound a disruption do they want?”

Pfizer is already the seventh largest advertiser in the US, according to Kantar Media data cited by The Wall Street Journal. Globally, in 2014 Pfizer spent $1.4 billion on advertising; Allergan spent $266 million; and Actavis, which acquired Allergan in November 2014 and took the drugmaker’s name, spent $387 million, according to Kantar Media. In comparison, Procter & Gamble—the world’s largest advertiser in 2014—spent $4.6 billion.

From January to June of this year, Pfizer spent $740 million while Allergan spent $144 million. Actavis spent $261 million in the same timeframe. 

The same agency executive noted, however, that it’s unlikely any significant changes to the drugmakers’ agency rosters will occur prior to September 2016. The deal is expected to close by the end of next year. 

Pfizer currently works with a global network of WPP creative agencies known as “Team Pfizer.” Team Pfizer is made up of more than 100 regionally based offices in 33 countries and works on more than 35 Pfizer brands. Pfizer is one of WPP’s largest clients.

WPP will not be alone, though, in wondering if Team Pfizer awaits a review of the business. At least 26 healthcare advertising agencies could stand to be affected by the deal, according to agency-supplied information published in the MM&M 2015 Agency issue. Nineteen companies listed Pfizer as one of their healthcare accounts, and another seven agencies listed Allergan as a healthcare account. 

Those twenty-six agencies span four agency networks: Omnicom, WPP, Interpublic Group and Publicis Groupe. 

Pfizer declined to discuss future marketing plans. Allergan did not respond to inquiries by press time. 

The CEO of a major agency network said his biggest fear is simply an overall slowdown in marketing spending. “Mergers and acquisitions create uncertainty,” he said, noting that he doesn’t anticipate many changes in 2016. 

“I can be nervous because there’s change,” the same executive added, with the caveat: “We have pretty solid relationships.”

In order to wade through that uncertainty, it’s helpful to look at Pfizer’s last megadeal—the acquisition of Wyeth in 2009—as a possible blueprint for how it may handle marketing divisions following the deal’s closing.

Pfizer announced its acquisition of Wyeth in January 2009 and closed the deal in October the same year. From 2008 to 2009, Pfizer’s advertising spend in professional healthcare journals dropped 22% from $47 million to $36 million, according to Kantar Media. Its spend did rebound somewhat the following year, rising 10% year-over-year to $40 million in 2010.  

Five months after Pfizer finalized the deal to acquire Wyeth, it consolidated all of the media buying for Wyeth’s DTC brands. The combined drugmaker eventually awarded an estimated $250 million in billings to Carat, according to Advertising Age. An in-house division at Wyeth had previously had the business.

After another review in September 2010, Carat kept the business, noting at the time that it would continue to be Pfizer’s AOR for DTC media planning and buying for its pharmaceutical business across all channels, Ad Age reported

If history is any indicator, in-house agencies employed by Allergan and Pfizer could face a review. One agency executive said: “Pfizer historically doesn’t do in-house agencies.” 

Pacific Communications is an in-house agency for Allergan. Pacific Communications President Craig Sullivan said in an email that it’s premature to comment on anything related to the merger, but that his shop “remains committed to supporting our Allergan clients.”

Pacific’s website currently features work for Allergan brands Botox, Latisse and Lastacraft, a prescription eyedrop brand, as well as Valeant’s Bausch & Lomb.  

Pfizer may not find much fat to trim at Allergan, however, as the company already slimmed margins last year to fend off a hostile takeover by Valeant. David Pyott, Allergan’s CEO at the time, devised a cost-savings plan as a way to appease investors before Valeant’s takeover fell through and the company was ultimately acquired by Actavis. 

Still, Allergan in 2015 launched “Actually She Can,” an unbranded social media campaign. Herm Cukier, VP of women’s healthcare for Allergan, described the initiative at the time as part of a long-term commitment to women: “This isn’t just a three-month campaign. In five years I hope we’ll look back and see that this a starting point to a more transformational approach.”

While Pfizer-Wyeth may hold a few clues as to how Pfizer-Allergan’s marketing strategy may begin to take shape, its future plans may be complicated by the fact that Pfizer has already undergone a recent consolidation of its major brands. 

In 2014 Pfizer completed a global creative review that concluded with that business being divvied up between three holding companies: WPP, Omnicom and Publicis. Ad Age reported at the time that the review was conducted through Pfizer’s procurement department.