Reasons Behind Merck’s Stock Surge by 70%

Merck’s stock saw a significant 67% jump between June 2025 and February 2026, driven more by investor enthusiasm than by substantial revenue and profit gains. Various factors contributed to this surge, including robust sales in the oncology segment, breakthroughs in the pipeline, and strategic acquisitions. However, the optimistic outlook was tempered when the company provided cautious guidance for 2026, causing a noticeable pullback in the stock’s momentum.

During the specified time frame, Merck’s stock price soared by 67%, with only a modest 1.7% increase in total revenues and a 2.9% boost in net income margin. The sharp 57% rise in the P/E multiple further fueled investor excitement. Key drivers of this upward trajectory included the strength of Keytruda sales in the oncology segment, a 9% growth in the Animal Health segment, successful pipeline execution with positive Phase 3 trial results, and a proactive approach to mergers and acquisitions, exemplified by the acquisition of Verona Pharma.

Despite the positive developments, Merck’s 2026 earnings per share guidance of $5.00-$5.15 reflected a significant impact from the acquisition of Cidara Therapeutics, causing a near-term earnings reset. The core investment debate surrounding Merck focuses on whether new product launches and pipeline progress can offset the anticipated loss of exclusivity for Keytruda in 2028, a product that constitutes nearly half of the company’s sales. While Keytruda and new launches show promise, concerns about the Gardasil franchise, declining forward estimates due to M&A costs, and the looming 2028 patent cliff contribute to a neutral sentiment among investors.

Bullish viewpoints highlight strong initial sales from Winrevair and Capvaxive, the extension of Keytruda’s life cycle, and the potential for future diversified growth post-2028. Conversely, bearish arguments emphasize the magnitude of the revenue cliff resulting from the Keytruda loss of exclusivity, high pipeline execution risks, and competitive pressures faced by new products. Navigating these contrasting perspectives requires a broader portfolio framework to manage inherent volatility and investment risks associated with individual stocks.

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