The Incretin Class: Three Compounds, One Research Trajectory

The short version

NextGen Peptides is a reading desk, not a store. It compiles what the published research literature actually reports about three peptides that define the current metabolic pharmacology frontier: semaglutide, tirzepatide, and retatrutide.

A peptide is a short chain of amino acids — the same building blocks as proteins, only far smaller and more targeted. These three are all incretin mimetics: they imitate hormones the gut releases after eating, signaling the pancreas, liver, and brain to regulate blood sugar and food intake. What separates them is how many receptors they activate. Semaglutide targets one (GLP-1). Tirzepatide targets two (GLP-1 and GIP). Retatrutide targets three (GLP-1, GIP, and glucagon), adding an energy-expenditure lever the other two lack.

This desk does one job: it reports what each compound was tested on, in which populations, and what the trial results actually showed. We use plain language and cite every claim. Two of the three are FDA-approved prescription medicines used by millions of people. One is investigational, still in Phase 3 trials. None of the content here is medical advice, none lists a dose, and none of it directs you to a source.

What are incretin peptides?

"Incretin" refers to gut hormones — most importantly GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide) — that are secreted in response to food entering the small intestine. Their job is to augment insulin release from the pancreas, suppress inappropriate glucagon, and send satiety signals to the brain. In people with type 2 diabetes or obesity, this system is blunted.

The compounds on this desk are synthetic peptides engineered to mimic or extend those signals, with chemical modifications that resist normal degradation and allow once-weekly dosing. They are not the same as the endogenous hormones they mimic. They are prescribed medicines or investigational drugs studied under clinical oversight — not supplements, not amino acid products, not nutritional agents.

Research-grade versions are sold by vendors for laboratory use outside clinical trials, carrying documented quality, purity, and regulatory risks that are distinct from the approved-product evidence base. This desk covers only the published clinical and preclinical science.

How these three relate to each other

The three compounds on this desk trace a single pharmacological progression, each adding a receptor target:

• Semaglutide is the reference point — a selective GLP-1 receptor agonist with a two-decade evidence base. Its STEP program documented a mean -14.9% body-weight change at 68 weeks in adults with obesity ^[4], and the SELECT trial added a 20% reduction in major cardiovascular events in non-diabetic individuals with obesity ^[3]. It is the most studied, most prescribed, and most regulated compound on this desk.
• Tirzepatide adds co-agonism at the GIP receptor, producing mean weight losses of up to -20.9% at 72 weeks in the SURMOUNT-1 trial ^[10]. In the direct SURMOUNT-5 head-to-head comparison (n=751), it outperformed semaglutide by roughly 6.5 percentage points (-20.2% vs -13.7%) ^[1].
• Retatrutide adds a third lever — the glucagon receptor — which drives thermogenesis and lipid mobilization beyond what GLP-1/GIP alone achieves. In its Phase 2 obesity trial it produced a mean -24.2% body-weight change at 48 weeks ^[15], currently the largest published weight loss from any single pharmacological compound in a controlled trial. Phase 3 data are pending.

For a structured side-by-side of these numbers, see the comparison page.

A note on how this desk reads the evidence

NextGen Peptides is a cross-referenced literature digest. Every quantitative claim on this site cites the trial it came from. Where study designs differed, we flag the methodological context: open-label versus blinded, Phase 2 versus Phase 3, industry-sponsored versus independent. Effect sizes are reported as the primary trials published them — means, hazard ratios, confidence intervals — not rounded summaries.

Where there are known safety signals (GI tolerability, gallbladder disease, lean-mass loss, weight regain after discontinuation) we report them the same way, from the same sources. The goal is a map of what is known, stated at the resolution the data support.