Merck Shares Plummets 1.34% as Regulatory Scrutiny and Sector Headwinds Push Stock to 127th in Market Activity

On October 7, 2025, Merck & Co. (MRK) closed with a 1.34% decline, trading with a daily volume of $0.83 billion, ranking 127th in market activity. The stock’s performance followed a mixed trading session influenced by regulatory developments and sector-specific dynamics.

Regulatory scrutiny intensified as the U.S. Department of Justice reportedly expanded its antitrust investigation into pharmaceutical pricing practices, with Merck’s diabetes and HIV treatment portfolios under closer review. Analysts noted that while the probe is not Merck-specific, its broader implications for the sector could pressure margins and R&D budgets. Additionally, a European Union court ruling on generic drug pricing timelines created uncertainty in international markets, where Merck holds significant revenue exposure.

Investor sentiment was further dampened by a revised earnings forecast from a key biotech partner, which indirectly affected Merck’s collaboration revenue streams. The adjustment, though unrelated to Merck’s core operations, prompted risk-off trading in healthcare equities, with Merck’s high-conviction pipeline stocks experiencing outflows. Short-term traders also reacted to a technical breakdown in the stock’s 50-day moving average, triggering algorithmic selling pressure.

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