Merck Shares Tumble on Regulatory Delays and Oncology Competition as Dollar Volume Slips to 109th

Merck (MRK) closed lower on Oct. 6, 2025, declining 0.44% with $1.04 billion in trading volume, ranking 109th among stocks by dollar volume for the session. The pharmaceutical giant's shares faced pressure amid mixed signals from its pipeline updates and broader market volatility.

Recent regulatory developments cast uncertainty over key product timelines. The FDA's revised guidance on antiviral therapies delayed potential approvals for Merck's experimental treatments, prompting cautious investor sentiment. Analysts noted the delay could impact near-term revenue visibility, though long-term growth prospects remain intact due to robust R&D spending and a diversified portfolio.

Market participants also weighed in on evolving competition in the oncology space. While Merck's immuno-oncology assets retain market share, emerging therapies from smaller biotech firms are compressing profit margins. Institutional investors adjusted position sizes as risk appetite waned, with fund flows showing a net outflow of $120 million across major asset managers.

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