Blue-chip drugmakers holding $200 billion in cash, mostly overseas, will start investing more of it in mergers and acquisitions after President Trump's tax overhaul slashed the cost of spending the money in the U.S., debt-ratings firm Moody's predicts.

A repatriation provision in the Tax Cuts and Jobs Act, approved by Congress in December and signed into law by Trump, allows U.S. companies to bring assets held overseas back to the U.S. without a penalty after paying a mandatory one-time fee of 15.5 percent on cash holdings and 8 percent on the remainder. Under the previous structure, the Internal Revenue Service typically would have assessed levies of about 30 percent, prompting firms that could get money less expensively through capital markets to simply pay for acquisitions with debt.

The tax bill changes the playing field for U.S corporations considerably, "both because the accumulated cash can be accessed more tax efficiently and, separately, because ongoing future cash flows can be accessed more tax efficiently," Michael Levesque, a senior vice president at the New York-based firm, told the Washington Examiner.

While corporate takeovers will be a priority for the 10 U.S.-based firms with investment-grade credit ratings that Levesque analyzed in a report released Tuesday, executives may also use the cash to start or increase dividends and share buybacks.

U.S. companies are required under current law to pay for such investor rewards with money taxed in the U.S., and they're generally required to use such funds when buying U.S. companies.

Since those are the areas where pharmaceutical firms want to invest most, and much of their cash is outside the U.S., they will benefit significantly now that "there's really no constraint on keeping the money abroad versus moving" once they've paid the repatriation charge, Levesque said.

Amgen, Pfizer, Gilead, and Celgene are the most likely to seek deals, Moody's projects, as they grapple with challenges from a shrinking market for some medications to the expiration of patents on others that will enable rivals to produce cheaper generic versions.

Pfizer's U.S. patent on Lyrica, a treatment for diabetic nerve pain, will expire in mid-2019, for instance, and Celgene will eventually have to grapple with producers of a generic version of Revlimid, a cancer drug that makes up 60 percent of its revenue, Levesque said.

Expiring patents on such products force pharmaceutical companies "to replenish their pipelines," Levesque said. "That's not always done internally. Many times, it's done through acquisitions."

The pace of dealmaking for pharmaceuticals is likely to pick up in the next six to 12 months, he added. The S&P pharmaceuticals index has climbed 8.1 percent in the past year, compared with a 21 percent increase on the broader S&P 500.

Corporate acquisitions are expected to increase outside the pharmaceutical industry, too, as U.S. businesses benefit from a reduction in the top tax rate to 21 percent from 35 percent, according to Wall Street economists and analysts.

Corporate takeovers had dwindled in the past two years to a comparatively small $1.3 trillion in the U.S., according to research firm Mergermarket, which tracks global dealmaking.