How GLP-1 and GIP Drugs Shut Down Hunger Neurons in the Brain | Research

The takeaway

Drugs like tirzepatide suppress appetite by inhibiting the brain's hunger-promoting AgRP neurons, and dual GIP/GLP-1 activation is more powerful than either alone.

Dual > Single
Combined GIP and GLP-1 receptor agonism inhibited hunger neurons and suppressed food intake more than either agonist alone

What the researchers found

Using fiber photometry in live mice, researchers discovered that GIP and GLP-1 play distinct roles in appetite regulation through AgRP neurons — the brain's key hunger-promoting cells. Endogenous GIP (but not GLP-1) was required for normal nutrient-triggered suppression of these hunger neurons. However, at pharmacologic doses, both GIP and GLP-1 analogs inhibited AgRP neurons.

Critically, dual GIP and GLP-1 receptor agonism (as in tirzepatide) more potently inhibited AgRP neurons and suppressed food intake than either agonist alone. The degree of neural inhibition directly correlated with how much each drug reduced eating.

Why it matters

Semaglutide and tirzepatide are blockbuster obesity drugs, but scientists still don't fully understand how they suppress appetite in the brain. This study identifies a specific neural mechanism — inhibition of AgRP hunger neurons — and reveals why dual agonists like tirzepatide may work better than GLP-1-only drugs like semaglutide. Understanding these pathways is essential for designing next-generation weight loss drugs that are more effective and have fewer side effects.

The numbers in context

Dual GIP/GLP-1 agonism > single agonism for AgRP inhibition · Neural inhibition magnitude proportional to food intake reduction · GIP required for normal nutrient-mediated AgRP suppression · GLP-1 not required for physiologic AgRP inhibition

How the study worked

Researchers used in vivo fiber photometry to monitor real-time activity of AgRP neurons in living mice. They tested the effects of endogenous incretin hormones (GIP and GLP-1) during normal feeding, as well as pharmacologic doses of incretin analogs, on AgRP neuron activity and food intake. They compared single versus dual receptor agonism.

Who was studied

Male mice studied with in vivo fiber photometry

What this study cannot tell us

This was a mouse study, and the neural circuits controlling appetite differ somewhat between mice and humans. The pharmacologic doses used may not directly correspond to clinical doses in humans. The study focused on one neural population (AgRP neurons) when incretin drugs likely affect multiple brain circuits.

How to read the evidence

This is a preliminary-grade mechanistic study in mice using advanced neuroscience techniques. While it provides important insights into how incretin drugs work in the brain, it has not been validated in humans.

When this study was published

Published in 2025 in the Journal of Clinical Investigation, a top-tier journal. This is very recent work at the forefront of obesity neuroscience.

The bigger picture

The obesity drug market is rapidly expanding, with next-generation triple agonists already in clinical trials. Understanding exactly how these drugs work in the brain — which neurons they target and why dual/triple agonism outperforms single targets — is the foundation for designing better drugs. This study provides a mechanistic explanation for tirzepatide's clinical superiority over semaglutide and points toward AgRP neurons as a key therapeutic target.

Questions still open

Do AgRP neurons respond the same way to incretin drugs in humans as they do in mice?
Could triple agonists (GLP-1/GIP/glucagon) produce even greater AgRP neuron inhibition?
Are the nausea side effects of these drugs also mediated through AgRP neuron pathways or separate circuits?

Common questions

What are AgRP neurons and why do they matter for weight loss drugs?

AgRP neurons are brain cells in the hypothalamus that drive hunger. When they're active, you feel hungry and seek food. GLP-1 and GIP drugs work in part by shutting these neurons down, which reduces appetite. This study shows that targeting both GIP and GLP-1 receptors simultaneously is more effective at silencing these hunger signals than targeting either one alone.

Does this explain why tirzepatide works better than semaglutide?

It provides a key piece of the explanation. Tirzepatide activates both GIP and GLP-1 receptors, while semaglutide only activates GLP-1 receptors. This study shows that dual activation shuts down hunger neurons more powerfully than single activation, which aligns with clinical trial data showing tirzepatide produces more weight loss than semaglutide.

Read the original research

Incretin receptor agonism rapidly inhibits AgRP neurons to suppress food intake in mice.

The Journal of clinical investigation, 135(21)

View on PubMed ↗Publisher’s paper ↗

Citation

McMorrow, Hayley E; Cohen, Andrew B; Lorch, Carolyn M; Hayes, Nikolas W; Fleps, Stefan W; Frydman, Joshua A; Xia, Jessica L; Samms, Ricardo J; Beutler, Lisa R. (2025). Incretin receptor agonism rapidly inhibits AgRP neurons to suppress food intake in mice.. The Journal of clinical investigation, 135(21). https://doi.org/10.1172/JCI186652