In a move that has sent shockwaves through the biotechnology sector, Merck announced on November 14, 2025, that it will acquire Cidara Therapeutics in a $9.2 billion all-cash deal. The agreement, which values Cidara at $221.50 per share—a staggering 109% premium over the previous day’s close—marks one of the year's most dramatic biotech takeovers. The transaction is expected to close in the first quarter of 2026, pending customary conditions, according to reporting from Stocktwits and multiple financial news outlets.
Cidara Therapeutics has been on a meteoric rise throughout 2025, with its stock surging more than 700% year-to-date. The company’s fortunes have been closely tied to its lead drug candidate, CD388, a long-acting antibody designed to prevent influenza infections in high-risk populations. The U.S. Food and Drug Administration has granted CD388 Breakthrough Therapy designation, a status that could accelerate the drug’s path to market. According to Stocktwits, late-stage clinical studies are underway, with more than 6,000 participants expected to be enrolled globally by the end of November 2025. These studies are focusing on vulnerable groups, including immunosuppressed patients who cannot receive seasonal flu vaccines and adults aged 65 and older.
Merck’s interest in Cidara is strategic and timely. The pharmaceutical giant faces the looming 2028 patent expiration of Keytruda, its blockbuster cancer therapy that generated over $25 billion in revenue in 2024. Losing exclusivity on Keytruda would leave a significant gap in Merck’s revenue stream, so the company has been aggressively building out its pipeline. The acquisition of Cidara follows Merck’s $10 billion purchase of Verona Pharma in July 2025, part of what many analysts describe as a broader wave of pharmaceutical dealmaking. Pfizer’s recent high-profile acquisition of obesity-drug developer Metsera for up to $10 billion underscores the competitive environment for innovative therapies.
The road to Merck’s acquisition of Cidara was anything but straightforward. According to Stocktwits and other financial sources, negotiations extended late into November 13, 2025, as Merck faced stiff competition from another unnamed pharmaceutical group. The intense bidding war reflects the growing importance of long-acting influenza prevention technologies, especially for populations that remain underserved by existing vaccines.
Despite the dramatic surge in Cidara’s stock price and the eye-popping premium offered by Merck, the reaction from major Wall Street brokerages was surprisingly muted. Almost immediately after the deal’s announcement, top firms downgraded Cidara to neutral stances. Morgan Stanley moved the stock to “Equal Weight,” JPMorgan shifted to “Neutral,” RBC Capital dropped it to “Sector Perform,” Needham went to “Hold,” and H.C. Wainwright also stepped back to “Neutral.” The consensus among analysts appears to be that, with the acquisition price set and the deal all but certain, Cidara’s shares have little room left to run. As one analyst put it, “The upside has been realized; now it’s a waiting game for the deal to close.”
Merck, for its part, has emphasized the strategic value of the Cidara acquisition. In a statement quoted by Stocktwits, Merck said the move “strengthens its respiratory pipeline ahead of the anticipated 2028 patent loss for Keytruda.” The company is betting that CD388 will become a cornerstone of its future respiratory offerings, providing a much-needed buffer as it navigates the post-Keytruda landscape. The FDA’s Breakthrough Therapy designation for CD388 could expedite regulatory review, potentially bringing the drug to market faster and giving Merck a leg up on competitors.
Retail investors, meanwhile, have been celebrating in online forums. On Stocktwits, sentiment for Cidara was described as “extremely bullish,” with message activity ranging from “extremely high” to “high.” Many users expressed gratitude to the Cidara team and congratulated fellow shareholders, noting that the deal delivered major gains for those who held on through years of uncertainty. “I’ve waited a long time for this outcome,” wrote one user, echoing a sentiment shared by many. Another added, “Congrats to all the holders—this is what we’ve been waiting for!”
Merck’s own stock, however, has not fared as well in 2025, declining 4% so far this year. Some analysts attribute this to investor concerns about the company’s heavy spending on acquisitions and the approaching patent cliff for Keytruda. Still, the company’s leadership appears undeterred, signaling that bold moves are necessary to secure future growth.
The Cidara deal is emblematic of a broader trend in the pharmaceutical industry, where established players are racing to acquire promising biotech firms in order to replenish aging pipelines and address looming patent expirations. The frenzy has been fueled by robust clinical data, speculation about potential auctions, and rising interest in therapies with strong commercial prospects—particularly in areas like influenza prevention, where unmet medical needs remain high.
Looking ahead, the focus will be on the continued progress of CD388’s clinical trials and the regulatory review process. With more than 6,000 participants expected to be enrolled by the end of November 2025, the global scale of the studies underscores both the ambition of the program and the high stakes involved. If successful, CD388 could offer a new standard of care for high-risk individuals who are poorly served by existing flu vaccines. For Merck, the acquisition represents a calculated gamble—one that could pay off handsomely if CD388 delivers on its promise.
For Cidara’s investors and employees, the deal is a validation of years of work and risk-taking. For Merck, it’s a bold step toward securing its future in an increasingly competitive pharmaceutical landscape. As the dust settles, all eyes will be on the progress of CD388 and the completion of the merger in early 2026. The outcome could reshape the market for influenza prevention—and set the tone for biotech dealmaking in the years to come.
With the ink barely dry on the agreement, both companies now face the task of integrating their operations and keeping the momentum going. The stakes couldn’t be higher, and the industry will be watching every step of the way.
