TRENTON, N.J. -- Pfizer and Botox maker Allergan are discussing a potential deal that could be the biggest of 2015, a year marked by a rapid-fire pace of megadeals, particularly in health care.

A merger could enable Viagra maker Pfizer, the world's second-biggest drugmaker by revenue, to surpass Switzerland's Novartis AG and regain the industry's top spot.

In separate statements, both companies last week said they were in "preliminary friendly discussions." Allergan Plc said there's no certainty the talks with Pfizer Inc. will lead to a deal.

The talks come amid the latest wave of health-care consolidation, which includes brand-name and generic drugmakers as well as insurers, pharmacy chains and drug wholesalers -- all groups trying to boost bargaining clout. Allergan, based in Dublin, is selling its generics unit to Israel's Teva Pharmacueticals Industries Ltd., the world's top generic drugmaker.

Generic competition to its blockbuster drugs, such as cholesterol-fighter Lipitor, is expected to cut Pfizer's sales by $28 billion from 2010 through next year. It's done three sizeable deals since 2000 to boost revenue.

A deal for Allergan would allow for additional growth, and Pfizer might pursue an "inversion." That's a tax-saving maneuver in which a U.S. company reincorporates in a country with a lower corporate tax rate.

Inversions have become a hot political topic, raising the ire of lawmakers in Washington and public-interest groups.

Pfizer, based in New York, spent months in the spring of last year pursuing another top 10 drugmaker, Britain's AstraZeneca PLC, in an attempted inversion, but those talks collapsed when the two sides couldn't agree on a price. Pfizer was willing to pay $118 billion.

With other companies announcing or pursuing inversions, however, the Obama administration acted.

By the end of the year, the U.S. Treasury Department had initiated new regulations designed to limit the financial benefits of inversions. The rules bar certain techniques that companies use to lower their tax bills and tighten ownership requirements.

Last week, billionaire investor Carl Icahn announced he was setting up a $150 million super PAC bent on revising U.S. corporate tax law and ending the practice of inversions, ratcheting up political pressure more.

Analysts who follow Pfizer were not surprised deal talks were underway but warned an inversion might trigger more pushback from Washington. That could compound public anger over soaring prices for prescription drugs, which have become another big issue in the 2016 presidential race.

Sen. Charles Schumer, D-New York, issued a statement last week saying, "The continued pursuit of inversions, mergers and foreign acquisitions of major U.S. companies for purely tax purposes shows there is a lot more work to be done to stop them."

Ian Sams, a spokesman for Hillary Clinton's campaign, said in a statement last week "Clinton is committed to cracking down on" inversions.

Pfizer said in its statement it won't comment on speculation regarding the terms of a potential transaction.

Buying Allergan would add its brand-name medicines for eye conditions, infections and heart disease to Pfizer's extensive portfolio of vaccines and drugs for cancer, pain, erectile dysfunction and other conditions.

Given Allergan's market capitalization of about $113 billion before deal talks surfaced, it would be the biggest buyout of the year, more expensive even than Anheuser Busch InBev's $106 billion bid for SABMiller.

And some industry analysts said the price tag for Allergan could be much higher.

According to SanfordBernstein analyst Dr. Timothy Anderson, an all-stock deal is likely, because Allergan shareholders would own at least 40 percent of the combined company, a level that would allow Pfizer to get full tax relief under Treasury's new ownership thresholds.

Pfizer's current tax rate is about 25 percent and Allergan's around 15 percent, he noted.

Beyond any potential tax benefits, Anderson called the deal a good fit.

"Allergan is (mostly) a U.S. company operating mainly in the primary care markets, which Pfizer understands well. The two organizations are geographically close, and the post-merger integration would therefore be easier than a trans-Atlantic deal," Anderson wrote. "Second, Allergan management is unlikely to be an obstacle to a transaction."