GSK to acquire efimosfermin from Boston Pharmaceuticals for $2bn to bolster liver disease pipeline

GSK plc (LSE/NYSE: GSK) has announced a definitive agreement to acquire Boston Pharmaceuticals’ lead investigational asset, efimosfermin alfa, in a deal worth up to $2 billion. The acquisition includes an upfront payment of $1.2 billion and potential milestone-based payments totaling an additional $800 million. Efimosfermin is a Phase III-ready fibroblast growth factor 21 (FGF21) analog, designed to treat and prevent the progression of steatotic liver disease (SLD), a condition that affects roughly 5% of the global population and currently lacks effective treatment options.

This strategic transaction strengthens GSK’s specialty medicine portfolio and advances its research focus on fibrosis, immunology, and targeted metabolic disorders. The asset complements GSK’s existing siRNA pipeline candidate, GSK’990, which also targets liver disease driven by metabolic and alcohol-related damage.

Why Is GSK Investing in Efimosfermin Now?

The acquisition of efimosfermin aligns tightly with GSK’s long-term strategy of developing precision-based treatments for chronic and underserved diseases. Efimosfermin is designed to address metabolic dysfunction-associated steatohepatitis (MASH), a progressive and fibrotic form of SLD, and is also being explored for alcohol-related liver disease (ALD). With its antifibrotic mechanism, the molecule has shown promising Phase II data that suggests it can reverse liver fibrosis and prevent progression to cirrhosis—outcomes that have been historically difficult to achieve.

According to GSK’s Chief Scientific Officer, Tony Wood, efimosfermin represents a potentially best-in-class therapy, citing its monthly dosing schedule, tolerability profile, and efficacy data in reversing fibrosis. These qualities could support broad adoption and define a new therapeutic benchmark in the hepatology space.

How Does Efimosfermin Work, and What Makes It Unique?

Efimosfermin is a long-acting, subcutaneous analog of FGF21, delivered as a once-monthly injection. FGF21 is a hormone that plays a central role in regulating lipid metabolism, glucose control, and energy expenditure. The investigational compound is designed to activate this pathway in patients with MASH and ALD to reduce hepatic steatosis, limit inflammation, and ultimately reverse fibrosis.

In a Phase II clinical trial presented at the American Association for the Study of Liver Diseases (AASLD) Annual Meeting in November 2024, efimosfermin demonstrated statistically significant improvements in fibrosis scores among patients with biopsy-confirmed moderate-to-advanced MASH (F2-F3). These results were achieved regardless of concurrent GLP-1 agonist use, underscoring efimosfermin’s independent therapeutic effect.

The candidate also showed positive cardiometabolic benefits, such as reduced triglyceride levels and improved glycaemic control—key comorbid factors in this patient population. With low immunogenicity and a long half-life, efimosfermin offers the convenience of monthly dosing, which may improve adherence and quality of life for chronic disease patients.

What Market Opportunity Is GSK Targeting with This Acquisition?

SLD—including MASH and ALD—has emerged as a growing global public health burden. ALD alone affects approximately 26 million people worldwide and, along with MASH, has become the leading cause of liver transplants in the United States. The costs of end-stage liver disease, which include liver cancer and transplantation, are disproportionately high. According to recent estimates, delaying disease progression could reduce healthcare costs in the U.S. by between $40 billion and $100 billion over the next two decades.

Despite this, treatment options remain limited. Current interventions primarily focus on lifestyle modifications or metabolic control. Efimosfermin, with its demonstrated fibrosis-reversing properties, enters this unmet therapeutic landscape with potential to radically improve patient outcomes and reduce long-term medical expenditures.

GSK anticipates a potential first regulatory approval and commercial launch of efimosfermin by 2029.

What Are the Financial and Transactional Details?

Under the terms of the acquisition, GSK will purchase Boston Pharmaceuticals‘ subsidiary BP Asset IX, Inc., gaining full development and commercial rights to efimosfermin. The upfront cash consideration is $1.2 billion, with up to $800 million in additional milestone-based payments contingent on clinical and regulatory success.

GSK will also be responsible for tiered royalty payments to Novartis Pharma AG, reflecting existing licensing agreements. The transaction will be recorded as a business combination on GSK’s books and is subject to standard regulatory approvals, including clearance under the U.S. Hart-Scott-Rodino Antitrust Improvements Act.

Evercore Partners International LLP acted as GSK’s exclusive financial advisor, with legal counsel from Cleary Gottlieb Steen & Hamilton LLP. Boston Pharmaceuticals was advised by Centerview Partners LLC and represented legally by Sullivan & Cromwell LLP.

What Are Analysts and Investors Saying About GSK’s Acquisition Strategy?

The acquisition of efimosfermin has sparked cautious optimism among investors and analysts. While the asset is still in development and revenue contribution is not expected until the next decade, market watchers view the move as evidence of GSK’s continued commitment to building a robust specialty medicine pipeline following the demerger of its consumer healthcare arm, Haleon.

Analysts have highlighted efimosfermin’s strong Phase II data and potential best-in-class profile as encouraging signs. The asset’s ability to be used in combination with GSK’990 enhances its strategic value, offering pipeline diversification and optionality for targeted combination therapies in SLD.

Despite the market’s broader concerns around pricing reform and macroeconomic headwinds, GSK’s acquisition has helped reassure investors about its long-term innovation trajectory. Some institutional investors have increased exposure following the announcement.

How Has GSK’s Stock Reacted, and What Is the Market Sentiment?

GSK’s shares on the New York Stock Exchange (NYSE: GSK) closed at $37.37 on May 12, 2025, up 2.05% from the prior session. Over the past month, the stock has climbed nearly 8%, reflecting renewed investor interest amid new pipeline developments and business realignment.

However, the stock has not been immune to market-wide headwinds. Pharmaceutical equities broadly came under pressure following a policy announcement from U.S. President Donald Trump, who proposed cutting prescription drug prices by up to 80%. The plan aims to benchmark U.S. prices to those in developed nations using a “most favoured nation” pricing model, potentially squeezing margins for drugmakers including GSK.

Following the announcement, GSK’s stock saw a temporary 3.2% decline in intraday trading, reflecting investor concern over pricing sustainability in its largest market. While the efimosfermin acquisition helped offset these losses, regulatory uncertainties remain a persistent overhang.

What Does Institutional Activity Reveal About Market Confidence?

Institutional sentiment towards GSK has been mixed. On the one hand, firms such as Forum Financial Management LP significantly increased their GSK holdings by over 160% in Q4 FY2024, suggesting confidence in the company’s direction. On the other hand, broader FII/DII data reveals dynamic positioning.

For instance, on May 8, 2025, foreign institutional investors (FIIs) were net buyers in Indian equities, with purchases totaling ₹2,007.96 crore. Meanwhile, domestic institutional investors (DIIs) recorded net outflows of ₹596.25 crore, according to Trendlyne data. Though not GSK-specific, these flows indicate shifting sentiment patterns in global pharma exposure amid sector rotation and defensive positioning.

In the U.S. and UK, institutional holdings in GSK have remained relatively stable. No major insider transactions or institutional divestitures have been reported since the efimosfermin announcement.

What’s Next for GSK and Efimosfermin?

GSK plans to initiate Phase III clinical trials of efimosfermin within the next year, with trial enrollment targeted for late 2025. The company will focus on developing both monotherapy and combination regimens with GSK’990, supporting a modular approach to treating various subtypes of SLD.

If successful, efimosfermin could become a flagship product in GSK’s hepatology franchise and a foundational treatment for liver fibrosis. Its potential for monthly dosing, positive metabolic effects, and anti-inflammatory benefits position it well for broad adoption pending regulatory approval.

Looking ahead, the investment underscores GSK’s strategic pivot toward higher-margin specialty medicines that align with its core R&D competencies in immunology, genetic science, and precision medicine.