Nature Metabolism Study: Cagrilintide-Retatrutide Combination Outperformed Single Drugs in Obese Rats

A study published online in Nature Metabolism on September 15, 2026 reports that combining two investigational obesity peptides, cagrilintide and retatrutide, produced greater weight loss in obese male rats than either drug alone or than matched combinations built around the approved drugs semaglutide and tirzepatide. The paper, "Cagrilintide and retatrutide combination therapy enhances weight loss and metabolic outcomes in obese male rats," was led by corresponding author Christoffer Clemmensen and lead author Jonas Petersen, with additional co-authors at the Novo Nordisk Foundation Center for Basic Metabolic Research and the Department of Biomedical Sciences at the University of Copenhagen, and the Department of Physiology at the University of Gothenburg.

Retatrutide is described in the paper as a unimolecular triple-hormone-receptor agonist that activates the GLP-1, GIP, and glucagon receptors. Cagrilintide is described as a co-agonist of the amylin and calcitonin receptors, the same mechanism used in Novo Nordisk's investigational combination drug CagriSema, which pairs cagrilintide with semaglutide. Combining retatrutide and cagrilintide engages five distinct receptors at once, which the authors describe as a "five-receptor polypharmacology" strategy.

According to the published abstract, daily co-administration of the two peptides in diet-induced obese male rats produced dose-dependent reductions in body weight and food intake that exceeded both equimolar monotherapies and matched-dose comparator combinations that substituted semaglutide or tirzepatide for one of the two drugs. The combination also improved circulating markers of metabolic health, including cholesterol, triglycerides, and insulin levels, relative to the comparators tested.

The researchers used pair-feeding and weight-matching experiments, methods that control for how much an animal eats or how much weight it has already lost, to test whether the added benefit of the combination was simply a byproduct of the animals eating less. The abstract states that the enhanced weight loss could not be explained by reduced food intake alone, which the authors say allowed them to separate effects that depend on weight loss itself from effects specific to the drug combination. Plasma proteomic profiling showed enrichment of bioenergetic, or energy-metabolism-related, biological processes in the combination-treated animals, while brain transcriptomic profiling identified converging neuronal programs linked to energy balance regulation.

The paper's authors disclosed several competing interests. According to the published conflict of interest statement, Jonas Petersen, Anders Bue Klein, and Christoffer Clemmensen are co-founders of Ousia Pharma, a biotech company developing obesity therapeutics, and Petersen, Christoffer Merrild, and Clemmensen are co-founders of Heureka Therapeutics, a biotech company developing cardiometabolic therapeutics. Clemmensen has received speaking fees from Novo Nordisk. Co-author Tune H. Pers has received research support from Novo Nordisk, holds Novo Nordisk stock through his household, and has received consulting fees from Eli Lilly and Zealand Pharma. The Novo Nordisk Foundation, which funds the university research center where most of the authors work, is a philanthropic foundation that is a majority shareholder of Novo Nordisk but operates separately from the company.

The study was conducted only in male rats fed a high-fat diet to induce obesity, and the findings have not been replicated in female animals or tested in humans. No registered clinical trial currently combines cagrilintide and retatrutide in people; each compound is being developed and tested separately, including in Eli Lilly's ongoing retatrutide obesity program and Novo Nordisk's cagrilintide programs, most prominently the cagrilintide-semaglutide combination CagriSema. Both cagrilintide and retatrutide remain investigational and are not approved by the FDA, the European Medicines Agency, or Australia's Therapeutic Goods Administration for any use.

As with other early-stage animal research on obesity drug combinations, these results identify a biological mechanism and a direction for further study rather than a therapy ready for clinical testing. Rodent metabolic studies do not always translate to the same magnitude of effect, or the same safety profile, in humans. Nothing in this study constitutes treatment or dosing guidance, and no combination product involving these two peptides has been approved or authorized by any regulator.