Richard DiMarchi and Matthias Tschöp—the chemist and physiologist whose work underlies the entire dual-incretin agonist field—just published a paper proposing that GLP-1 activation may not actually be necessary for effective weight loss. Their alternative: a GIP/glucagon dual agonist with zero GLP-1 activity at all.

The paper, in Molecular Metabolism on April 16, is the kind of intellectual move that doesn’t get much oxygen in the daily noise of GLP-1 launches and Phase 3 readouts but probably should. Every weight-loss drug currently on the market or in late-stage development—semaglutide, tirzepatide, retatrutide, Foundayo, MariTide, VK2735, CagriSema, survodutide—relies on GLP-1 receptor agonism as a central mechanism. If the people who built the most successful dual incretin agonist in pharmaceutical history are now saying GLP-1 may be replaceable, that’s worth paying attention to. (STAT News)

The Mechanistic Argument

The team synthesized a peptide that activates both GIP and glucagon receptors but has been engineered to have no detectable GLP-1 activity. They then dosed obese mice and obese cynomolgus monkeys at exposures higher than what’s typically used with GLP-1-containing drugs, and produced weight loss that—at those doses—was comparable to what GLP-1-containing drugs achieve at their standard doses.

The mechanistic claim is that the weight loss is being driven by a different pathway than the appetite suppression that has defined the GLP-1 era. Glucagon receptor activation drives energy expenditure—it stimulates hepatic gluconeogenesis, lipolysis in adipose tissue, and increases metabolic rate. GIP-mediated effects on adipocyte function appear to contribute to the fat-loss specificity. Add the two together at sufficient dose, and you get a drug that—in animals—produces comparable weight loss without engaging the appetite-suppression pathway that produces most of the nausea and gastrointestinal side effects associated with GLP-1 drugs.

That last part is what makes the argument practically interesting. Nausea and vomiting are the dose-limiting toxicity of every approved GLP-1 drug. Discontinuation rates of 5–18% across the Phase 3 obesity trials are largely driven by GI tolerability. If a non-GLP-1 mechanism can produce comparable weight loss without that ceiling on dosing, the implications for patient experience, dose escalation, and long-term adherence are substantial.

The Honest Caveats

This is preclinical data. The authors are the first to say so.

Animal models—even nonhuman primate models—do not transfer cleanly to humans. The history of obesity drug development is littered with compounds that produced beautiful weight loss in mice and failed catastrophically in human trials. GLP-1 receptor agonism, ironically, is one of the few mechanisms that has translated reliably from animal preclinical data to human Phase 3 outcomes. The “drop GLP-1” thesis would, by definition, be giving up that translational track record in exchange for a hypothesis that hasn’t yet been tested in humans.

The paper was funded by BlueWater Biosciences, a biotech in which DiMarchi and Tschöp have a stake. That’s not disqualifying—much of the most important obesity drug research is funded by drug companies with commercial interest in the outcome—but it should be on the reader’s mind when interpreting the framing.

The mouse and monkey doses required to produce the comparable weight loss were higher than what GLP-1 drugs use. Whether that translates to a human dosing regimen that is practical, tolerable, and commercially viable is exactly the kind of thing only a Phase 1 study can establish. None has been initiated yet.

Why This Matters

Two things, both consequential.

First, the GLP-1 dogma was always provisional. Semaglutide and tirzepatide work, dramatically, in ways nothing before them did. That commercial success calcified an assumption that GLP-1 receptor agonism is the necessary backbone of any future obesity drug. The DiMarchi/Tschöp paper challenges that assumption with the credibility of having designed the dual agonist that everyone is currently chasing. If they’re right, the next-generation pipeline could look meaningfully different from the current consensus.

Second, the current pipeline is committed to GLP-1 as a foundational mechanism. Every late-stage obesity drug other than amylin agonists (Viking’s VK3019, Pfizer’s PF-3944, Alveus’s ALV-200) builds on GLP-1 receptor activation. If the GIP/glucagon-only thesis turns out to be clinically viable, the companies that have made GLP-1 the foundation of their pipeline strategy will face a different competitive landscape than the one they’re currently operating in.

What to Watch

Three things will determine whether this becomes a real shift or a footnote.

A first-in-human study of the GIP/glucagon-only molecule (or a successor compound from the same chemistry) is the necessary next step. Without Phase 1 data, the argument remains a preclinical hypothesis—provocative, but not actionable. The closest current human evidence is from Boehringer’s survodutide, a GLP-1/glucagon dual agonist that just produced 16.6% weight loss in its first Phase 3 trial, and from earlier glucagon-receptor exploration in metabolic disease. Neither tested the GIP/glucagon-only configuration the DiMarchi paper specifies.

The competitive response from the major obesity drug developers will be telling. If Lilly, Novo, Amgen, or Viking quietly initiate GIP/glucagon programs over the next twelve months, that’s the strongest endorsement of the thesis. If they don’t, it suggests they read the argument as preclinical-only and are content to keep building on what’s already working in human data.

The translational risk is real. The paper proposes a mechanistic alternative that—if validated—would represent a substantial pivot for obesity pharmacology. If it fails to translate, it joins a long list of preclinical findings that didn’t survive contact with human biology. Either outcome is informative.

For the full evidence picture on the existing GLP-1 family—including dose-response, mechanism, evidence tier, and trial portfolio—our tirzepatide, semaglutide, and retatrutide compound articles cover the current state of play.

References

1. Researchers behind GLP-1 obesity drugs advance new approach: Drop GLP-1 as a target. STAT News. April 16, 2026. STAT
2. DiMarchi RD, Tschöp MH, et al. Molecular Metabolism. April 2026.
3. Boehringer Ingelheim’s survodutide achieved significant weight loss of 16.6% in Phase III SYNCHRONIZE-1. April 28, 2026. Boehringer Ingelheim