GLP-1 and glucagon come from the same gene.
| Stat | Value |
|---|---|
| Single precursor protein that produces both hormones | Proglucagon |
| Average body weight loss with retatrutide (48 weeks, 12mg) | 24.2% |
| Receptors targeted by retatrutide: GLP-1, GIP, glucagon | 3 |
| GLP-1 and glucagon's effects on blood sugar | Opposite |
Key Takeaways
- Shared origin: Both GLP-1 and glucagon are cleaved from proglucagon — but in different tissues, producing hormones with opposite blood sugar effects.
- Glucagon's role: Raises blood sugar by triggering liver glucose release; promotes fat burning (lipolysis) — the body's emergency fuel-mobilization system.
- GLP-1's role: Lowers blood sugar, slows digestion, suppresses appetite — broadly counters glucagon's metabolic effects post-meal.
- The paradox explained: Glucagon burns fat through a pathway that is separate from its blood sugar-raising effects. Triple agonists exploit this by activating glucagon signaling in fat tissue while using GLP-1 and GIP components to keep blood sugar stable.
- Retatrutide data: 24.2% average body weight loss over 48 weeks in Phase 2 — the strongest efficacy data of any drug in this class so far.
- Real limitation: Higher weight loss with glucagon co-agonism may come with trade-offs in tolerability that are still being characterized in Phase 3 trials.
That shared origin is more than a biological curiosity — it is the reason the newest and most powerful weight loss drugs are built the way they are. To understand why retatrutide outperforms semaglutide by nearly 10 percentage points of body weight, you need to understand what glucagon actually does and why targeting it — despite appearing counterintuitive — unlocks a fat-burning pathway that GLP-1 alone cannot reach.
Glucagon: the hormone that gets blamed unfairly
Glucagon has an image problem.
In the context of diabetes and metabolic health, it is almost always discussed as the villain — the hormone that raises blood sugar when insulin is trying to lower it. And that framing is not wrong, exactly. Glucagon is produced by alpha cells in the pancreas and its primary job is to signal the liver to release stored glucose (glycogenolysis) and manufacture new glucose (gluconeogenesis) when blood sugar drops too low.
But glucagon does something else entirely, something that gets far less attention in mainstream discussions: it promotes lipolysis — the breakdown of stored fat into free fatty acids that can be burned for energy. This is glucagon's other job, and it operates largely independently of what is happening with blood sugar.
When you fast overnight, glucagon rises and keeps your blood sugar from cratering — that is the well-known effect. But at the same time, glucagon is also signaling fat cells to release stored lipids. The two effects travel together in normal physiology, which is why they were long assumed to be inseparable.
GLP-1: the appetite brake glucagon doesn't have
GLP-1 is produced in an entirely different location.
L-cells in the small intestine and colon release GLP-1 when food arrives. It does the opposite of glucagon in nearly every way that touches blood sugar: it stimulates insulin secretion, suppresses glucagon release (particularly post-meal), slows gastric emptying so food energy enters the bloodstream more gradually, and signals the brain to reduce appetite and food intake.
After a meal in a healthy person, this GLP-1 signal is what brings blood sugar back toward normal. It is also why you eventually feel full and stop eating — the signal reaches the hypothalamus and brainstem and creates satiety. The problem is that natural GLP-1 lasts only about two minutes in the bloodstream before DPP-4 enzymes break it down. The signal is real but fleeting.
The tension between GLP-1 and glucagon is real and physiologically important. After eating, GLP-1 suppresses glucagon release, which is part of how it prevents post-meal blood sugar spikes. In type 2 diabetes, this suppression is blunted — glucagon stays too high after meals, contributing to elevated post-meal blood sugar. Semaglutide addresses this directly: it suppresses glucagon secretion after meals, which is one of several mechanisms behind its blood sugar benefits.
Semaglutide lowers post-meal glucagon by roughly 30–40% in clinical studies. This is not a side benefit — it is one of the core mechanisms through which it improves blood sugar control in people with type 2 diabetes, operating alongside its effects on insulin secretion and appetite.
The paradox of glucagon in weight loss drugs
Here is the question that stops most people: if glucagon raises blood sugar, why would you want a weight loss drug to activate glucagon receptors?
This is where the biology gets genuinely interesting. The glucagon receptor is expressed in multiple tissues — the liver (where it raises blood sugar), fat cells (where it promotes lipolysis), and the brain (where it has appetite-suppressing effects of its own). The blood sugar-raising effect and the fat-burning effect are mediated by the same receptor, but they happen in different tissues and can, in principle, be decoupled — at least partially — by carefully controlling the hormonal environment the drug creates.
Triple agonists like retatrutide are designed around exactly this insight. By simultaneously activating GLP-1 receptors and GIP receptors — both of which produce powerful insulin-stimulating and blood-sugar-lowering effects — the drug creates a metabolic backdrop in which activating glucagon receptors does not produce dangerous hyperglycemia. The blood sugar-raising effect of glucagon is essentially overridden by the insulin-stimulating effects of GLP-1 and GIP, while the fat-burning lipolytic effect is allowed to proceed.
The result is a drug that is reaching into a fat-burning pathway that single or dual agonists cannot access — and the clinical data suggests this matters enormously.
Retatrutide Phase 2: what 24.2% body weight loss actually means
Numbers this large deserve context.
Semaglutide at its 2.4mg weekly dose (Wegovy) produces approximately 15% average body weight loss over 68 weeks. Tirzepatide (Mounjaro/Zepbound), which targets both GLP-1 and GIP receptors, produces approximately 22.5% over 72 weeks at the highest dose. Retatrutide, the first triple agonist to publish Phase 2 results, showed 24.2% average body weight loss at the 12mg dose over 48 weeks — and notably, the curve had not plateaued at the end of the study period.
That trajectory — weight still falling at week 48 — is part of what makes these results notable. Standard GLP-1 agonists tend to plateau at around 6–12 months as the body adapts. The glucagon component in retatrutide may be contributing to continued fat mobilization beyond the point at which pure GLP-1/GIP agonism levels off.
| Drug | Receptors Targeted | Avg. Weight Loss | Study Duration | Status |
|---|---|---|---|---|
| Semaglutide (Wegovy) | GLP-1 | ~15% | 68 weeks | Approved |
| Tirzepatide (Zepbound) | GLP-1 + GIP | ~22.5% | 72 weeks | Approved |
| Retatrutide | GLP-1 + GIP + Glucagon | ~24.2% | 48 weeks | Phase 3 |
Where both hormones come from: the proglucagon story
Both GLP-1 and glucagon are cut from the same cloth.
Proglucagon is a single 160-amino-acid precursor protein encoded by the GCG gene. Depending on which tissue expresses it, the protein gets cleaved into completely different products:
In pancreatic alpha cells, proglucagon is processed primarily into glucagon — the blood-sugar-raising hormone. In intestinal L-cells and neurons, the same protein is processed instead into GLP-1 and GLP-2 (plus a few smaller peptides). The tissue-specific processing enzymes — primarily prohormone convertase 2 in the pancreas and prohormone convertase 1/3 in the gut and brain — determine which hormone gets produced.
This shared origin is not just a curiosity. It explains why GLP-1 and glucagon have structural similarities (both are 29-30 amino acid peptides with related sequences) even though they act on different receptors and produce opposite blood sugar effects. It also means that drugs designed to target GLP-1 signaling were always going to eventually lead researchers toward glucagon signaling — the two were always part of the same biological system.
The GCG gene does not "choose" which hormone to make. The pancreas and the gut read the same genetic instruction and produce different outputs. Understanding this makes the triple agonist strategy obvious in retrospect — the hormones were related all along, and their effects in fat tissue were always available to be leveraged.
What this means if you're deciding between drug options
If you are currently taking a GLP-1 agonist and wondering whether a triple agonist would make a difference, the answer depends on your specific goals and history.
For people who have reached a plateau on semaglutide — where weight loss has stalled despite continued use — the addition of GIP and glucagon receptor activation represents a genuinely different pharmacological approach, not just a larger dose of the same thing. Tirzepatide is already available and approved. Retatrutide is in Phase 3 trials, with a regulatory submission expected in 2025 or 2026.
One honest limitation worth naming: the glucagon component that makes these drugs more effective may also contribute to a more complex side effect profile. Nausea, vomiting, and gastrointestinal discomfort are common to the entire drug class, but adding glucagon activation adds another layer of pharmacological activity that is still being characterized in large-scale trials. The 24.2% weight loss figure comes from a Phase 2 study — Phase 3 results will provide a clearer picture of what the full benefit-risk profile looks like in a larger, more diverse population.
Frequently Asked Questions
Does semaglutide block glucagon entirely?
No. Semaglutide suppresses post-meal glucagon secretion — it reduces the inappropriate glucagon spikes that occur after eating in people with insulin resistance or type 2 diabetes. It does not block glucagon's fasting activity, which is important for preventing hypoglycemia during periods without food.
If glucagon burns fat, why don't people just take glucagon?
Because glucagon's fat-burning and blood-sugar-raising effects are largely inseparable in normal physiological conditions. Administering glucagon alone produces significant hyperglycemia, which is harmful. The triple agonist approach allows the fat-burning benefit to be accessed while using GLP-1 and GIP signaling to neutralize the blood sugar effect.
Is retatrutide available as a prescription?
As of early 2026, retatrutide is in Phase 3 clinical trials and is not yet approved for prescription use. Phase 3 results are expected to support a regulatory submission, but approval timelines depend on regulatory agency review. Ask your prescriber for current status.
Why does the incretin-glucagon system matter more than just "eating less"?
Because appetite and fat storage are hormonally regulated in ways that willpower alone cannot override. The GLP-1/glucagon system is part of the biological machinery that determines how much you eat and how efficiently your body stores or burns the energy from that food. Modifying that system pharmacologically changes the setpoint — it doesn't just make eating less temporarily easier.
This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before starting any medication or treatment.
