What Is GIP?

What Is GIP?

Glucose-dependent insulinotropic polypeptide (GIP) is a hormone produced by cells in the upper small intestine. Like GLP-1, GIP is an incretin hormone -- meaning it is released after eating and helps regulate the body's blood sugar response to meals. GIP was actually the first incretin hormone discovered, identified in the 1970s before GLP-1 research began.

How GIP Works

When food enters the digestive system, GIP is released into the bloodstream and acts on the pancreas to stimulate insulin secretion. This effect is glucose-dependent: GIP primarily triggers insulin release when blood sugar levels are elevated, which helps reduce the risk of hypoglycemia.

Beyond insulin, GIP also appears to play roles in:

• Fat metabolism: GIP receptors are found in adipose (fat) tissue, where the hormone may influence how the body stores and uses fat.
• Bone health: Some research suggests GIP may have protective effects on bone density.
• Appetite regulation: GIP receptors are present in brain regions involved in appetite and satiety, though the exact mechanisms are still being studied.

Dual GIP/GLP-1 Receptor Agonists

Traditional GLP-1 receptor agonists -- such as semaglutide (Ozempic, Wegovy) and liraglutide (Victoza, Saxenda) -- target only the GLP-1 receptor. Tirzepatide is the first medication to act on both the GIP and GLP-1 receptors simultaneously. This dual-receptor approach is sometimes called a "twincretin" because it engages both arms of the incretin system.

By activating both receptors, tirzepatide may produce additive or complementary effects on insulin secretion, blood sugar regulation, and appetite. Clinical trial data have shown that tirzepatide achieves greater A1C reductions and weight loss compared to GLP-1-only medications, though individual results vary.

Mounjaro and Zepbound: The Only Dual Agonists

As of this writing, tirzepatide is the only FDA-approved dual GIP/GLP-1 receptor agonist. It is marketed under two brand names:

• Mounjaro -- approved for type 2 diabetes management
• Zepbound -- approved for chronic weight management in adults with obesity (BMI of 30 or greater) or overweight (BMI of 27 or greater) with at least one weight-related condition

No other dual GIP/GLP-1 receptor agonist has received FDA approval, though several are under investigation in clinical trials.

Why the Dual Mechanism Matters

The inclusion of GIP receptor activation may help explain why tirzepatide has demonstrated some of the largest A1C reductions and weight loss results seen in clinical trials of incretin-based medications. In the SURPASS clinical trial program, tirzepatide showed statistically superior A1C reduction compared to semaglutide. In the SURMOUNT program for weight management, tirzepatide demonstrated average weight loss exceeding 20% of body weight at the highest dose.

However, it is important to note that more research is needed to fully understand the long-term implications of dual-receptor activation. Patients should discuss the potential benefits and risks with their healthcare provider to determine whether a dual GIP/GLP-1 agonist is appropriate for their situation.