Lilly agrees to acquire SiteOne Therapeutics for up to $1 billion
Lilly's up-to-$1 billion purchase of SiteOne Therapeutics adds a non-opioid pain candidate that is ready for Phase 2 testing, but no trial timing, data or approval path has been disclosed.
Eli Lilly and Company has agreed to acquire SiteOne Therapeutics, a private biotechnology company developing non-opioid pain medicines, in a deal that could pay SiteOne shareholders up to $1.0 billion in cash [1]. The two companies announced the definitive agreement on May 27, 2025 [1].
The transaction brings Lilly STC-004, a drug that targets a sodium channel called Nav1.8 and is described in the announcement as "Phase 2 ready" for the treatment of pain [1]. SiteOne says it develops highly selective small molecule inhibitors of Nav1.7, Nav1.8 and other ion channels to treat pain, cough and conditions involving hyperexcitability of the peripheral nervous system, the nerves outside the brain and spinal cord [1]. The company is also working on separate candidates for chronic cough and chronic ocular surface pain [1].
The $1.0 billion total includes an upfront payment plus later payments tied to regulatory and commercial milestones, according to the announcement [1]. How the money splits between the upfront amount and the milestones was not disclosed, and neither company gave a date for closing beyond saying the deal is subject to customary closing conditions [1]. Lilly said it will determine the accounting treatment under Generally Accepted Accounting Principles when the transaction closes, after which the deal will be reflected in Lilly's financial results and financial guidance [1].
Mark Mintun, Lilly's group vice president for neuroscience research and development, said in the announcement that "the global burden of chronic pain continues to increase, and an effective non-opioid treatment remains elusive" [1]. He added that Lilly is "eager to continue the development of STC-004 with the outstanding SiteOne team as part of our efforts to advance novel, addiction-free pain therapies" [1].
John Mulcahy, chief executive officer and cofounder of SiteOne, said the company has spent more than a decade working toward "safer, more effective, non-opioid therapies for patients suffering from pain" and that Lilly's "global capabilities and neuroscience leadership will accelerate our efforts to realize the full potential of STC-004" [1].
For Lilly, J.P. Morgan Securities LLC is acting as exclusive financial advisor and Jones Day as legal counsel; for SiteOne, Centerview Partners LLC is exclusive financial advisor and Skadden, Arps, Slate, Meagher & Flom LLP and Cooley LLP are legal counsel [1].
Why it matters for patients
Chronic pain is common and growing worldwide, and the announcement states that an effective non-opioid treatment has remained out of reach [1]. SiteOne was founded around the goal of developing pain medicines without what it describes as the significant addiction potential and side effects of opioids [1]. A new non-opioid option would matter to patients who cannot take opioids, do not tolerate them, or want to avoid them, though nothing in the announcement shows that STC-004 works or is safer than existing treatments.
STC-004 is not approved, and the announcement gives no timeline for a Phase 2 trial, later-stage testing or a regulatory decision [1]. The release also does not report results from any earlier human studies of STC-004, so its effectiveness and side effects in people have not been established here [1]. Patients waiting for a new class of pain medicine would still be looking at a drug that has not yet entered mid-stage testing, and Lilly's own filing language notes that there is no guarantee the acquisition will yield commercially successful products [1].
The announcement does not mention GLP-1 medicines, weight loss or diabetes; STC-004 is described only as a pain treatment [1].
What happens next
The acquisition still has to clear customary closing conditions, and no expected closing date was given [1]. Once it closes, Lilly will set the GAAP accounting treatment and fold the deal into its reported results and guidance [1]. Lilly said it intends to continue developing STC-004, but whether that means a Phase 2 study starts in 2025, 2026 or later has not been reported [1].
Sources
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