The GIP Paradox: Why Both Activating and Blocking the Same Receptor Can Help with Weight Loss | Research

The takeaway

Both GIP receptor agonism (as in tirzepatide) and antagonism (as in MariTide) provide additive weight loss when combined with GLP-1 receptor activation — a seeming paradox that this review traces from preclinical roots to clinical outcomes.

Both agonism and antagonism work
The central paradox: activating and blocking the same GIP receptor both produce additive weight loss when combined with GLP-1 — a puzzle driving major drug development programs

What the researchers found

The review synthesizes evidence supporting the paradox:

- GIP receptor agonism (tirzepatide): Activating both GIP and GLP-1 receptors produces greater weight loss and metabolic improvement than GLP-1 alone — demonstrated in clinical trials leading to tirzepatide's approval

- GIP receptor antagonism (maridebart cafraglutide/MariTide): Blocking GIP while activating GLP-1 also enhances weight loss — demonstrated in early clinical data

- The paradox is supported by: human genetic evidence (GIPR loss-of-function variants associated with lower BMI), rodent genetic knockout models, and preclinical pharmacology in rodents and non-human primates

- The review highlights where early preclinical findings successfully predicted clinical efficacy and where the translation was less straightforward

Why it matters

Understanding the GIP paradox is critical for the next generation of obesity drugs. If both agonism and antagonism work, it suggests the GIP system is more complex than a simple on/off switch. Resolving this paradox could reveal new mechanisms for weight loss and lead to even more effective peptide drugs — potentially with different side effect profiles that allow more patients to benefit.

How the study worked

Narrative review examining human physiology of GIP, human genetic evidence (loss-of-function variants), rodent genetic models (GIPR knockout), preclinical pharmacology studies in rodents and non-human primates, and clinical development data for tirzepatide and MariTide.

What this study cannot tell us

This is a review without original data. The paradox itself remains unresolved — the review examines the evidence motivating both programs but does not provide a unified mechanistic explanation. Some preclinical findings in rodents may not translate directly to humans. The clinical data for GIPR antagonism (MariTide) are still early-stage compared to the extensive tirzepatide trial program.

How to read the evidence

This is a narrative review synthesizing human genetics, preclinical studies, and clinical trial data. The evidence spans from observational genetics to randomized clinical trials, providing a strong multi-level foundation for the paradox.

When this study was published

Published in 2025, this review captures the state of understanding at a pivotal moment when both GIPR agonist and antagonist programs have advanced to late-stage clinical development.

The bigger picture

The GIP paradox is arguably the most important unresolved question in incretin pharmacology. Tirzepatide is already a commercial success, and MariTide is advancing through clinical trials. If the paradox can be explained — perhaps through concepts like receptor desensitization, tissue-specific signaling, or biased agonism — it would fundamentally reshape our understanding of metabolic peptide pharmacology and open new drug design strategies.

Questions still open

Does GIP receptor agonism work through a fundamentally different mechanism than antagonism, or do both ultimately converge on the same downstream pathway?
Could a patient's genetic GIP receptor variants predict whether they respond better to agonism or antagonism?
Will GIP antagonism-based drugs like MariTide have different side effect profiles than agonist-based approaches like tirzepatide?

Common questions

How can both activating and blocking the same receptor cause weight loss?

This is the central paradox and it's not fully resolved. One theory is that chronic GIP receptor stimulation may eventually desensitize the receptor, effectively producing a similar outcome as blocking it. Another possibility is that GIP acts differently in different tissues — so agonism might help in some places while antagonism helps in others. The answer likely involves complexity in how the GIP signaling system operates across the body.

What are tirzepatide and MariTide?

Tirzepatide (Mounjaro/Zepbound) is an approved drug that activates both GIP and GLP-1 receptors, producing dramatic weight loss. MariTide (maridebart cafraglutide) is an experimental drug that blocks GIP receptors while activating GLP-1 receptors, and has also shown impressive weight loss in early trials. They represent opposite approaches to the same receptor — yet both seem to work.

Read the original research

The Premise of the Paradox: Examining the Evidence That Motivated GIPR Agonist and Antagonist Drug Development Programs.

Journal of clinical medicine, 14(11)

View on PubMed ↗Publisher’s paper ↗

Citation

Douros, Jonathan D; Mowery, Stephanie A; Knerr, Patrick J. (2025). The Premise of the Paradox: Examining the Evidence That Motivated GIPR Agonist and Antagonist Drug Development Programs.. Journal of clinical medicine, 14(11). https://doi.org/10.3390/jcm14113812