GLP-1 and glucagon are often described as opposites: GLP-1 lowers blood sugar and curbs appetite, while glucagon raises blood sugar by prompting the liver to release glucose. Yet the newest obesity drugs deliberately activate both receptors at once. The reason is that glucagon also burns energy, and pairing it with GLP-1 cancels out its blood-sugar downside.
Because these hormones interact, many readers ask is GLP-1 the same as insulin.
What is glucagon and what does it do?
Glucagon is a hormone made by the alpha cells of the pancreas, and it is essentially insulin's counter-regulatory partner. When blood sugar falls, glucagon is released to protect you from going too low.
Glucagon's classic actions
- Raises blood glucose by triggering the liver to break down stored glycogen (glycogenolysis) and to manufacture new glucose (gluconeogenesis).
- Mobilizes fat by promoting lipolysis and fatty-acid oxidation in the liver.
- Increases energy expenditure and has thermogenic effects, a property that turns out to be central to its use in weight-loss drugs.
That last point is the key. Beyond its role in glucose, glucagon increases how many calories the body burns at rest, which is why drug developers became interested in adding it to incretin therapies.
Glucagon and energy expenditure
The thermogenic side of glucagon is well documented. A NIH review on glucagon regulation of energy expenditure describes how glucagon increases oxygen consumption and resting energy expenditure, and notes that sustained glucagon action raises overall calorie burn. The NCBI Endotext chapter on glucagon physiology similarly outlines its roles in glycogenolysis, gluconeogenesis, lipolysis, and fatty-acid oxidation. These catabolic, energy-burning properties are precisely what makes glucagon attractive as one ingredient in a weight-loss molecule, provided its glucose-raising tendency can be contained.
What does GLP-1 do, and why is it the opposite?
GLP-1 (glucagon-like peptide-1) is an incretin hormone from the gut. Its name reflects that it is structurally related to glucagon, yet its metabolic effects point in the opposite direction.
GLP-1 lowers blood sugar by stimulating glucose-dependent insulin release, suppresses glucagon secretion, slows stomach emptying, and reduces appetite through the brain. For a fuller treatment of its biology, see our guide to GLP-1 and GIP. The short version: GLP-1 is a brake on blood sugar and appetite, while glucagon is, in part, an accelerator on blood sugar and energy burn.
How do GLP-1 and glucagon compare directly?
| Action | GLP-1 | Glucagon |
|---|---|---|
| Source | Gut L-cells | Pancreatic alpha cells |
| Effect on blood glucose | Lowers it | Raises it |
| Insulin secretion | Stimulates (glucose-dependent) | Indirect / mixed |
| Appetite | Strongly suppresses | Can reduce intake at pharmacologic levels |
| Energy expenditure | Largely neutral | Increases (thermogenic) |
| Liver fat | Reduces over time | Promotes fat oxidation |
Reading the table, the apparent conflict is obvious in one row, blood glucose, and complementary in several others, including energy expenditure and liver fat.
Why would a drug activate both opposing receptors?
The strategy is called co-agonism or multi-agonism. The idea is to capture glucagon's benefits, more calories burned and more liver-fat oxidation, while using GLP-1's blood-sugar-lowering power to neutralize glucagon's tendency to raise glucose.
The energy-expenditure advantage
Most weight-loss drugs work almost entirely by reducing how much you eat. Glucagon-receptor activity adds a second lever: increasing how much energy you burn. This matters because the body fights weight loss with adaptive thermogenesis, a slowing of metabolism that undermines diet-only approaches. A drug that nudges energy expenditure upward, rather than letting it fall, directly counters that defense, which may be part of why glucagon-containing agonists have produced such large and durable results. According to a phase 2 trial of the triple agonist retatrutide published in the New England Journal of Medicine, adding glucagon activity to GLP-1 and GIP produced striking weight loss, with the highest dose group losing roughly 24 percent of body weight at 48 weeks.
Retatrutide and the triple-agonist approach
Retatrutide is an investigational "triple G" agonist that targets the GLP-1, GIP, and glucagon receptors simultaneously. The glucagon component is included specifically for its thermogenic and hepatic-fat effects. You can read a focused breakdown in our article on retatrutide's mechanism of action and a plain-language overview in what is retatrutide.
A separate phase 2a trial in Nature Medicine reported that retatrutide markedly reduced liver fat in people with metabolic dysfunction-associated steatotic liver disease, consistent with glucagon's known role in driving hepatic fat oxidation.
How the three receptors divide the labor
It helps to think of each receptor as covering a different metabolic job. GLP-1 handles appetite suppression, satiety, and glucose-dependent insulin release. GIP supports the incretin effect and may improve how fat tissue handles nutrients, while also appearing to soften the nausea associated with strong GLP-1 signaling. Glucagon contributes energy expenditure and liver-fat reduction. No single hormone does all of this, which is the entire argument for multi-agonism: stack mechanisms that individually have ceilings, and the combined effect can exceed what any one pathway delivers alone.
How is the blood-sugar paradox resolved?
This is the crux of the design. Glucagon alone would worsen blood sugar, which is dangerous in someone with diabetes. But when glucagon activity is delivered together with strong GLP-1 (and GIP) activity, the incretin components stimulate insulin and suppress the net glycemic effect. In trials, balanced triple agonists improved, rather than worsened, glucose control while delivering glucagon's metabolic upside.
Why balance and dosing matter
The ratio of glucagon to GLP-1 activity is carefully tuned. Too much glucagon relative to GLP-1 could raise blood sugar or heart rate; too little would forfeit the energy-expenditure benefit. This balancing act is why these molecules are engineered with specific receptor potencies rather than simply combining three separate drugs. Compared with single-receptor drugs in our GLP-1 receptor agonist drug list, triple agonists are a deliberately different design philosophy.
What does this mean for weight loss?
The practical takeaway is that "opposing" hormones are only opposites on the single axis of blood sugar. On the axes that matter most for obesity, appetite, energy expenditure, and liver fat, GLP-1 and glucagon can be made to work as a team. Combining them is one of the main reasons triple agonists have produced the largest weight-loss numbers reported so far in obesity pharmacology.
A note on heart rate and monitoring
Because glucagon-receptor activity can modestly raise heart rate and influence blood pressure, trials of glucagon-containing agonists track cardiovascular measures closely. This is an active area of study, and it is one reason these drugs are advanced cautiously through phased trials rather than rushed to market. The promise is real, but so is the need for careful long-term safety data before glucagon co-agonism becomes routine, and our overview of retatrutide and heart rate digs into what the trial data show so far.
Frequently Asked Questions
If glucagon raises blood sugar, is retatrutide unsafe for diabetics?
In trials, the GLP-1 and GIP components offset glucagon's glucose-raising effect, and overall glycemic control improved rather than worsened. That said, retatrutide is still investigational and not FDA-approved, and any diabetes treatment must be supervised by a clinician.
Does glucagon cause weight loss on its own?
Glucagon increases energy expenditure and fat oxidation, but its blood-sugar effects make it unsuitable as a standalone weight-loss drug. Its value emerges only when paired with incretin hormones that counter the glucose downside.
Is GLP-1 just "anti-glucagon"?
Not exactly. GLP-1 does suppress glucagon secretion, but it has many independent actions, boosting insulin, slowing gastric emptying, and reducing appetite, that go well beyond simply opposing glucagon.
Why is it called glucagon-like peptide?
GLP-1 is produced from the same precursor gene region and shares structural similarity with glucagon, hence the name, even though its metabolic effects on blood sugar are largely opposite.
This article is for general education and is not medical advice. Retatrutide is investigational and not approved by the FDA. Talk with a qualified healthcare professional before starting, stopping, or changing any medication.
