Scientists have solved a puzzling question about a brain receptor involved in appetite: How can activating it and blocking it both lead to weight loss? The answer appears to depend on location.
In a study involving mice, researchers at the University of Cambridge found that drugs targeting the glucose-dependent insulinotropic polypeptide receptor, or GIPR, can influence body weight through separate regions of the brain. Activating the receptor in the brainstem reduced appetite, while blocking it in the hypothalamus strengthened the brain’s response to signals of fullness.
The findings, published in Nature Metabolism, could help explain why obesity medicines with seemingly contradictory mechanisms can produce similar outcomes. They may also point toward more effective combinations of GIPR-targeting treatments and drugs that act on the GLP-1 receptor, the target of medicines such as Wegovy and Ozempic.
As we know, substantial and sustained weight loss is often difficult to achieve through changes in diet and physical activity alone. Newer obesity medications work partly by influencing the biological systems that control hunger, fullness, and blood sugar.
Wegovy and Ozempic, for example, activate the glucagon-like peptide 1 receptor, commonly known as GLP-1R. Other treatments act on GLP-1R and GIPR at the same time.
That is where the scientific puzzle begins. Mounjaro and Zepbound activate GIPR as part of their mechanism. MariTide, an investigational medicine in phase 3 clinical trials, takes the opposite approach by blocking GIPR while activating GLP-1R. Both strategies can support weight loss, even though one turns the GIP receptor on and the other prevents it from working.
The Cambridge research suggests these approaches are not producing the same effect in the same place. Instead, they appear to engage distinct brain circuits that ultimately lead to reduced food intake and body weight.
To investigate, the researchers used genetically engineered mice in which GIPR had been removed from selected parts of the brain. Some mice lacked the receptor in the brainstem, an area near the spinal cord that helps regulate appetite and nausea. Others lacked it in the hypothalamus, which plays a central role in hunger, energy balance, and body-weight regulation. A third group of mice had not been genetically modified and served as a control.
The animals received different combinations of three types of treatment: a GIPR agonist that activated the receptor, a GIPR antagonist that blocked it, and a GLP-1-based drug. The researchers then measured how much the mice ate, how their body weight and fat mass changed, how well they regulated blood sugar, and which parts of their brains became active.
By comparing the results among the three groups, the scientists were able to identify the brain regions required for each treatment to work.
The experiments indicated that GIPR agonists depend largely on the brainstem. When the receptor was activated in this area, the mice ate less and lost weight. But when GIPR had been removed from the brainstem, the appetite-reducing effect was weakened, suggesting that this region is a key site of action for drugs that stimulate the receptor.
This helps explain how medicines that activate both GIPR and GLP-1R can influence eating behavior. Their effects are not limited to the digestive system or the pancreas; they also involve neural circuits that help determine when an animal stops eating.
GIPR antagonists worked differently. Their weight-loss effects depended more heavily on the hypothalamus. In this part of the brain, GIPR appears to act like a “brake,” reducing the strength of fullness signals coming from the brainstem.
Blocking the receptor releases that brake. As a result, signals telling the brain that the body has had enough food may become more powerful.
This means that activating and blocking GIPR can each reduce eating, but they reach that outcome through different routes. Activation directly engages appetite-suppressing pathways in the brainstem, while antagonism appears to make the hypothalamus more receptive to signals of satiety. That distinction may also explain why both strategies can complement GLP-1 medicines.
The findings offer a clearer biological explanation for the design of MariTide, which combines GIPR antagonism with GLP-1R activation. Because the two components may act through separate but interacting circuits, combining them could potentially produce a greater effect than targeting either pathway alone.
The researchers also found signs that GIPR antagonism could strengthen the effects of medicines aimed at the amylin receptor, another emerging target for obesity treatment. If that finding translates beyond mice, blocking GIPR might eventually be used to enhance several different types of weight-loss drugs — not only GLP-1 therapies.
Dr. Jo Lewis, the study’s first author from the Institute of Metabolic Science at the University of Cambridge, said:
Understanding which brain circuits respond to these medications — and how they do so — could help us design better drugs that produce more weight loss with fewer side effects, and which might work in combination with other obesity medicines to even greater effect…
Our work also strengthens the idea that the brain is central to obesity treatment. Obesity drugs are not acting simply on the gut or pancreas. Instead, they have important effects on specific, identifiable brain circuits that regulate appetite and food intake.
The research provides a useful framework for understanding an apparent contradiction in obesity pharmacology. Drugs that activate GIPR and drugs that block it are not necessarily cancelling out the same biological process. They may be acting in different brain regions, on different circuits and at different stages of the body’s appetite response.
However, the work was conducted in mice. Further research will be needed to determine how closely the same mechanisms apply to humans and whether targeting these pathways in combination can reliably improve weight loss, blood sugar control, or tolerability in patients.
Even so, the results underline an important shift in the science of obesity treatment. The effects of these medicines cannot be understood solely by studying the gut, insulin production, or digestion. Their success may depend just as much on where — and how — they alter communication within the brain.
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Source: “Scientists solve the mystery of a brain “switch” that can trigger weight loss in opposite ways,” ScienceDirect, 8/15/26
Source: “Distinct brain regions mediate regulation of food intake in response to GIPR agonism or antagonism,” Nature Metabolism, 7/24/26
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