When European drugmakers promoted billions of dollars in investments to build manufacturing plants in the United States earlier this year, they had hoped to gain immunity from President Trump’s tariff threats.

Those plans appear to have paid off. Mr. Trump’s announcement on Thursday of 100 percent tariffs on brand-name drugs imported to the United States contained a carve out for drugmakers that were already building new factories in the country.

Although some European officials and companies appeared confident on Friday that existing trade agreements and investments would shield them from this exceedingly high tariff rate, others were cautiously awaiting further details. As with many aspects of Mr. Trump’s turbulent trade policy, key information on how the new levies would be put in place has not yet been revealed.

Still, the pharmaceutical companies and their investors believe that Mr. Trump’s tariff announcement will potentially have little effect on them.

On Friday, Novartis, one of the world’s biggest drugmakers, said that a new pharmaceutical tariff “should have no impact” on its activities, pointing to a $23 billion investment in U.S. infrastructure and the construction of new sites in the country.

“We are working to ensure that all major Novartis medicines for U.S. patients are manufactured in the U.S.,” the Swiss-based company said in a statement. “Against this backdrop, the announced 100 percent tariff should have no impact on Novartis.”

Roche, a colossal player in the global health care industry, pointed out that its U.S. subsidiary, Genentech, is a “shovels-in-the-ground company” that recently began construction on a $700 million facility in Holly Springs, N.C., calling it “the initial phase of Genentech and Roche’s $50 billion investment in U.S. manufacturing, infrastructure, and R&D.”

The drugmakers’ announcements come as Mr. Trump has pushed for more production in the United States and railed against the higher cost of medicines. Before his tariff announcement on Thursday, Mr. Trump floated the idea of imposing a 200 percent tariff on drugs imported into the United States. But he also said he would give companies at least a year to move the manufacturing sites to U.S. shores.

Many American pharma companies have moved production of their blockbuster medications to Europe to take advantage of the tax benefits. The largest players may be largely exempt from the newest tariffs, but it’s less clear how smaller drugmakers that do not have the capacity to build American factories will fare.

The European Union’s trade deal with the United States includes a provision keeping pharmaceutical tariffs at 15 percent, the across-the-board rate that the bloc had negotiated. On Friday, officials at the European Commission, the European Union’s executive arm, emphasized that deal, arguing that the bloc’s companies would not be subject to the new tariff.

“This clear, all-inclusive 15 percent tariff ceiling for E.U. exports represents an insurance policy that no higher tariffs will emerge for European economic operators,” Olof Gill, a commission spokesman, said in a statement.

Still, there was some lack of clarity about whether the terms of that trade deal would hold. Mr. Gill said that Maros Sefcovic, the E.U. trade commissioner, had not yet spoken to his American counterpart on Friday, but would within the coming days.

Pharmaceutical products and chemicals are the European Union’s No. 1 export to the United States, and span the weight-loss blockbuster Ozempic, cancer treatments, cardiovascular drugs and flu vaccines. Most are name-brand drugs that yield a large profit in the American market.

Ireland in particular is home to more than 90 pharmaceutical companies, according to its Foreign Direct Investment Agency, and many of the biggest American drugmakers have operations in that nation. Last year, the pharma industry in Ireland, which includes multinational companies like Eli Lilly, exported 58 billion euros, or about $68 billion, in pharmaceutical and chemical products to the United States.

Many of Britain’s largest pharma companies may also be insulated because they have a substantial manufacturing presence in the United States and recently announced new investments. AstraZeneca, which is based in Cambridge, England, said in July that it would invest $50 billion in the United States by 2030, including building a manufacturing plant in Virginia.

During Mr. Trump’s state visit to Britain last week, GSK announced a $1.2 billion investment in manufacturing, artificial intelligence and advanced digital technologies in the United States, bringing its investment over the next five years to $30 billion.

Even so, some drugmakers were still scrambling to figure out the implications of Mr. Trump’s latest announcement.

A spokesman for Germany’s Merck said the company was “engaging with the U.S. administration to understand details of this tariff and impact on our business and the patients we serve.” Two other large German pharmaceutical companies, Bayer and Boehringer Ingelheim, said that it was too early to comment.

The United States is an important market for Germany’s pharma industry, which last year sold roughly 27 billion euros of its drugs there, according to the country’s statistics office, Destatis.

European officials remained wary. Bernd Lange, who heads the committee for international trade in the European Parliament, slammed the latest round of tariffs as arbitrary and unfair. He warned that unless European companies were exempted from them under the U.S. trade deal, the bloc should retaliate.

“If these new tariffs really do come into force, then the E.U. must immediately put countermeasures on the table,” Mr. Lange said in a statement.

The main pharmaceutical lobby group in Europe, known as EFPIA, warned that tariffs on medicines would “create the worst of all worlds,” adding that “urgent discussions are needed on how to avoid any tariffs on medicines that harm patients in the E.U. and the U.S.”

Although Britain had reached an agreement with the United States to limit the impact of tariffs, the provision to protect pharmaceutical companies is indeterminate. The two countries agreed in May that they would be focused on “securing significantly preferential outcomes for the export of pharmaceutical products” from Britain to the United States.

But it is unclear what that will mean in practice now that Mr. Trump has announced higher tariffs.

“We know this will be concerning for industry, which is why we’ve been actively engaging with the U.S. and will continue to do so over the coming day,” a British government representative said in a statement on Friday.

William Bain, the head of trade policy at the British Chambers of Commerce, said that he expected the investment plans from Britain’s pharma companies to protect them from new duties.

“The expectation is that the U.K.’s trade deal should provide a framework for exemptions which can give certainty to the U.K.’s leading pharmaceutical firms,” he added.