Pharmaceutical stocks in Asia fell, but big pharma groups in Europe in the U.S. were largely unaffected after President Trump announced a 100% tariff on drugs by companies that aren’t building plants in the U.S.

“Starting October 1st, 2025, we will be imposing a 100% Tariff on any branded or patented Pharmaceutical Product, unless a Company IS BUILDING their Pharmaceutical Manufacturing Plant in America,” Trump posted on his social media site, Truth Social, on Thursday without providing details.

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In Europe, small and midsize companies took the hardest hit, as shares in the biggest companies opened lower but pared losses and some even bounced back later. Asian pharma stocks fell across the board and led stock markets lower. Meanwhile, big pharma stocks rose slightly in U.S. premarket trading.

The tariff announcements are “not quite as big a move as it appears at first sight,” said Neil Shearing, group chief economist at Capital Economics, in a note.

The exemptions for generic drugs and companies that are constructing manufacturing facilities in the U.S. will help lower the effective tariff rate, as many global pharmaceutical companies either already have some production in the U.S. or have announced plans to do so, Shearing said.

Among European companies, shares in AstraZeneca, GSK, Novartis, Roche and Sanofi—all of which have outlined plans for multibillion-dollar investments in the U.S. in coming years—traded broadly flat or rose slightly after opening in the red. Novo Nordisk shares fell 1.5%, while smaller groups including Genmab and Zealand Pharma fell close to 2%.

The levies might have a limited impact on major players with established U.S. footprints, Vontobel analysts said. There is ample room for interpretation of Trump’s announcement, but Novartis and Roche should avoid a hit given construction already underway, while Galderma and other small groups with limited U.S. presence may be more vulnerable, the analysts said.

In Asia, Japan’s Nikkei Stock Average closed 0.9% lower, weighed down by chip and pharmaceutical companies. Sumitomo Pharma, Chugai Pharmaceutical and Daiichi Sankyo declined 3.45%, 4.8% and 2.0%, respectively.

SK Biopharmaceuticals and Samsung Biologics fell 3.5% and 2.15%, respectively, in South Korea. The benchmark Kospi ended 2.5% lower.

Chinese pharma companies were among the biggest losers on Hong Kong’s Hang Seng Index, with Alibaba Health Information Technology and JD Health International down 4.6% and 4.3%, respectively. WuXi AppTec lost 3.3%.

Citi Research analysts said the tariff impact on China’s pharmaceutical and biotechnology companies should be limited, given that China only accounted for about 4% of U.S. drug imports in 2024.

While Chinese firms have minimal drug sales exposure to the U.S., “investors may have concerns regarding Chinese biotechs’ U.S. expansion,” Jefferies equity analysts said in a note. “At this stage, most companies are at least 1-2 years away from potential U.S. commercialization, and most are receiving low-teen percentage royalties from U.S. pharma.”

Furthermore, the majority of Chinese biotech companies have U.S. partners and are therefore exempt from tariffs, Jefferies analysts added.

Pharmaceutical stocks also fell in India, with Sun Pharmaceutical Industries last down 2.9% and Natco Pharma dropping 3.6%.

Barclays economists said the proposed U.S. tariff only applies to branded or patented pharmaceuticals, which will likely help limit India’s exposure, while its overall domestic orientation will help cushion the blow.

Other tariffs Trump announced Thursday include duties on large trucks and home goods. All of them will begin Oct. 1, he said.

Heavy trucks brought from outside the U.S. will be hit with a 25% tariff, Trump said.

Write to Kimberley Kao at kimberley.kao@wsj.com and to Billy Gray at william.gray@wsj.com

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