Roche is licensing an experimental obesity treatment from South Korea’s Hanmi Pharmaceutical designed to do something today’s blockbusters cannot: melt fat while preserving muscle.
Announced August 24, 2026, the deal gives Roche rights to HM17321 outside South Korea for $190 million upfront plus up to $2.3 billion in development, regulatory and commercial milestones, plus royalties. Hanmi will finish the Phase 1 trial before Roche takes over.
Why lean mass became the issue
GLP-1 drugs produce weight loss on a scale previously achievable only through surgery. What they do not do is discriminate.
Rapid weight loss from any cause removes both fat and lean tissue, and studies of GLP-1 therapy have found a meaningful share of the weight lost is not fat. Some lean mass reduction is expected and appropriate — a smaller body needs less muscle to move it — but the proportion has been higher than many clinicians consider desirable.
The concern is sharpest in older patients. Muscle mass and strength decline with age regardless, and accelerating that loss risks frailty, falls and reduced functional independence. Losing weight while becoming weaker is not straightforwardly a health improvement for someone in their seventies.
There is also a metabolic argument. Muscle is where most glucose disposal occurs, so losing it may undermine some of the metabolic benefit the weight loss was meant to deliver — and lower muscle mass reduces resting energy expenditure, potentially making regain easier.
What HM17321 does differently
It is a urocortin 2 analogue — an injectable designed to activate a pathway that stimulates muscle growth and fat metabolism.
That is mechanistically distinct from GLP-1 drugs, which work substantially by suppressing appetite and slowing gastric emptying so people eat less. Reduced intake drives weight loss, and the body draws on whatever it has, including muscle.
An agent acting on muscle growth and fat metabolism directly addresses body composition rather than energy balance. “The paradigm of obesity treatment is evolving beyond simple weight reduction toward improving body composition,” said Hanmi’s R&D head.
Complement or competitor?
The framing matters commercially, and the likely answer is complement.
A drug preserving muscle without producing the dramatic weight loss GLP-1s achieve would struggle as monotherapy. Combined with a GLP-1, it could allow the same fat loss with better composition — which is a more plausible product than a replacement.
That is why large companies are buying into this category rather than betting against GLP-1s. The dominant drugs are not going away, and the value lies in improving what they deliver.
How early this is
Phase 1 began in November 2025, and Hanmi will complete it before Roche assumes development.
Phase 1 in obesity establishes safety, tolerability and pharmacokinetics, with early signals on weight and possibly body composition. It does not establish that muscle is preserved over the months during which meaningful weight loss occurs — which is the entire claim.
Hanmi says it holds a head start over rivals working on similar approaches, and the category has attracted substantial interest, with several companies pursuing muscle-preserving agents through different mechanisms.
The measurement problem
A difficulty rarely mentioned in coverage: demonstrating muscle preservation is harder than demonstrating weight loss.
Weight is trivially measured. Body composition requires imaging, and different methods disagree. More importantly, muscle mass and muscle function are not the same thing — preserving measured lean tissue while strength and physical performance decline would be a hollow result.
Regulators are likely to want functional endpoints, not just imaging, and those are slower and harder to move. That requirement may prove the real barrier for this category rather than the underlying pharmacology.
What the deal structure signals
$190 million upfront for a Phase 1 asset is substantial, and reflects competition rather than certainty. Multiple companies want a position in muscle-sparing obesity therapy, and waiting for Phase 2 data means bidding against everyone who has seen it.
The obesity market is fragmenting into sub-problems
This deal is one instance of a broader shift in how the industry approaches obesity, and the direction is informative.
The first generation competed on a single axis: how much weight comes off. That contest has largely been decided, and the leading agents produce reductions approaching what surgery achieves.
Attention has consequently moved to everything else. Muscle preservation is one front. Others include tolerability, since gastrointestinal side effects drive substantial discontinuation; oral formulations, since weekly injection limits uptake; weight regain after stopping, which is near-universal and turns treatment into a lifetime commitment; and demonstrating benefit on specific comorbidities to support reimbursement.
Each of those is a distinct product opportunity, which is why a category dominated by two companies is nonetheless attracting large deals from others. The unmet needs are no longer about the primary effect — they are about everything surrounding it, and those are problems a differentiated mechanism can address without having to beat GLP-1s at their own game.
The remaining $2.3 billion is milestone-contingent and mostly will not be paid unless the drug succeeds through registration — the standard structure that makes headline deal values a poor guide to committed capital. Business news, not investment advice.