Weight loss peptides have split into two camps, and most people don't even realize it. One camp suppresses appetite through the amylin system. The other burns calories through the glucagon pathway. [[Cagrilintide|12]] and [[Mazdutide|13]] represent the sharpest version of this split. Same goal, radically different biology.

If you've been following the GLP-1 wave (semaglutide, tirzepatide), you already know those drugs work. But they're not the only game. Both cagrilintide and mazdutide introduce mechanisms that GLP-1 alone can't touch. Understanding what each one actually does at the receptor level isn't academic trivia. It determines which compound makes sense for your specific situation.

The amylin pathway: how cagrilintide talks to your brain

Amylin is the hormone nobody talks about. Your pancreatic beta cells secrete it alongside insulin every time you eat. Natural amylin has a half-life of about 13 minutes, so it works in short bursts. It hits receptors in the area postrema, a small region in the brainstem that sits outside the blood-brain barrier. This is key. Most peptides can't cross the BBB directly. Amylin doesn't have to. The area postrema is a circumventricular organ, one of a handful of brain structures that can detect circulating hormones without barrier protection.

From the area postrema, the satiety signal propagates to the nucleus of the solitary tract (NTS) and then to the lateral parabrachial nucleus (LPBN). This is a completely different neural circuit than the one GLP-1 uses through the hypothalamus. Different wiring, different subjective experience. People on amylin analogs tend to report that food simply becomes less interesting, rather than the nausea-driven appetite suppression some experience with high-dose GLP-1 agonists.

[[Cagrilintide|12]] is a long-acting amylin analog engineered by Novo Nordisk. The critical modification: extending the half-life from 13 minutes to roughly 5-7 days. One subcutaneous injection per week. A 2025 study published in eBioMedicine confirmed that cagrilintide lowers body weight specifically through brain amylin receptors 1 and 3 (AMY1R and AMY3R). These receptors are formed by the calcitonin receptor combining with receptor activity-modifying proteins (RAMPs). Different RAMP combinations create different amylin receptor subtypes, and AMY1R and AMY3R turned out to be the ones that matter for weight loss.

What does amylin actually do beyond appetite? It slows gastric emptying (you feel full longer), suppresses postprandial glucagon release (less hepatic glucose dumping after meals), and appears to improve insulin sensitivity through mechanisms that are still being mapped. The gastric emptying effect overlaps with what GLP-1 agonists do, but the neural pathway is distinct.

Cagrilintide monotherapy: what the data shows

Novo Nordisk ran a dedicated Phase 3 trial for cagrilintide as monotherapy. The numbers: 11.8% mean body weight reduction versus 2.3% with placebo over 68 weeks. Among 3,417 participants receiving cagrilintide, 31.6% achieved weight loss of 15% or more, compared to 4.7% on placebo.

These are solid numbers for monotherapy. Not earth-shattering compared to tirzepatide's 22.5% in SURMOUNT-1, but remember: cagrilintide works through a completely different receptor system. The real power play isn't cagrilintide alone. It's the combination.

The REDEFINE 1 trial tested CagriSema, a fixed-ratio combination of cagrilintide and semaglutide. The results, published in the New England Journal of Medicine: 20.4% mean body weight reduction versus 3.0% with placebo at 68 weeks. Sixty percent of participants lost 20% or more. Twenty-three percent lost 30% or more. And 88% of participants with prediabetes returned to normoglycemia.

That 30% weight loss number is significant. It approaches what bariatric surgery delivers, and it's happening with a weekly injection. The logic is elegant: stack amylin-mediated satiety on top of GLP-1-mediated appetite suppression, and you get additive effects because the two systems operate through separate neural circuits.

The glucagon pathway: how mazdutide burns fuel

Now flip the entire paradigm. [[Mazdutide|13]] isn't about suppressing appetite through a different brain region. It's about cranking up energy expenditure at the metabolic level.

Mazdutide is a synthetic analog of oxyntomodulin, a gut hormone that naturally activates both GLP-1 and glucagon receptors. Developed by Innovent Biologics, it became the world's first approved GCG/GLP-1 dual receptor agonist. The GLP-1 component does what you'd expect: appetite suppression, delayed gastric emptying, improved insulin secretion. But the glucagon component is what makes mazdutide fundamentally different from semaglutide or tirzepatide.

Glucagon receptor activation in hepatocytes stimulates glycogenolysis, gluconeogenesis, and lipid oxidation. In plain terms: the liver starts breaking down fat stores and converting them to energy at an accelerated rate. The effect extends beyond the liver. Glucagon signaling promotes thermogenesis in brown adipose tissue, directly increasing calorie burn even at rest. This is the metabolic equivalent of turning up the thermostat.

The conceptual model is appealing: GLP-1 receptor activation mimics the effects of dieting (eat less), while glucagon receptor activation mimics the effects of exercise (burn more). You get both in one molecule.

There's a catch, though. Glucagon raises blood sugar. That's literally its primary physiological function. So a glucagon agonist in a weight loss drug sounds counterproductive for anyone with diabetes. Mazdutide gets around this because the GLP-1 component's insulin-stimulating effect counterbalances the glucagon-driven glucose production. The net effect on glycemia is actually favorable, but the balance matters and titration is critical.

Mazdutide clinical data: Phase 3 across multiple trials

The data set for mazdutide has expanded rapidly.

GLORY-1 (weight management): At week 48, the 6 mg dose produced 14.01% mean body weight reduction versus 0.45% with placebo. Nearly half (49.5%) of participants in the 6 mg group lost 15% or more body weight.

GLORY-2 (obesity, higher dose): The 9 mg dose delivered 20.08% mean body weight reduction at week 60 in participants without type 2 diabetes. This puts it in the same territory as CagriSema and tirzepatide 15 mg.

DREAMS-3 (head-to-head vs semaglutide): This is the big one. In Chinese patients with type 2 diabetes and obesity, mazdutide showed superiority to semaglutide on the composite primary endpoint of HbA1c below 7.0% and 10% or greater body weight reduction at week 32. Mean weight loss was 10.29% with mazdutide versus 6% with semaglutide. Two Phase 3 studies (DREAMS-1 and DREAMS-2) were published back-to-back in Nature, showing HbA1c reductions of 1.57% with 4 mg and 2.15% with 6 mg versus 0.14% with placebo.

The DREAMS-3 head-to-head data is particularly interesting because it shows the glucagon component isn't just about weight. It independently improves glycemic control beyond what GLP-1 alone achieves, likely through direct effects on hepatic glucose metabolism and lipid oxidation.

Mechanism comparison: why the pathway matters

Here's where it gets practical. These two peptides attack obesity through genuinely different biological strategies:

Cagrilintide's strategy: reduce caloric intake by enhancing satiety signals through the brainstem amylin circuit. You eat less because your brain genuinely registers fullness earlier and more strongly. The effect is primarily central (brain-mediated). Energy expenditure stays roughly the same; weight loss comes from the caloric deficit.

Mazdutide's strategy: reduce caloric intake through GLP-1 appetite suppression AND increase caloric expenditure through glucagon-driven thermogenesis and lipid oxidation. Weight loss comes from both sides of the energy balance equation.

This distinction has real-world implications. If your primary struggle is appetite control, if you find yourself eating not because you're hungry but because satiety signals aren't strong enough, the amylin pathway targets that specific dysfunction. If your metabolism has slowed significantly (common after extended dieting, in hypothyroid conditions, or simply with age), the glucagon-mediated metabolic boost addresses that problem directly.

Side effect profiles

Both compounds cause gastrointestinal side effects. That's the universal tax on anything that touches GLP-1 receptors or slows gastric emptying.

Cagrilintide's profile leans toward nausea and injection site reactions, generally mild and transient. Because it doesn't activate GLP-1 receptors directly (that's semaglutide's job in the CagriSema combination), standalone cagrilintide has a somewhat gentler GI profile than pure GLP-1 agonists.

[[Mazdutide|13]] carries the standard GLP-1 side effects (nausea, diarrhea, decreased appetite) plus the theoretical glucagon-related risks. In practice, the GLORY and DREAMS trials showed that the GI adverse events were mostly mild to moderate and decreased over time with dose titration. Heart rate increases have been observed, which is consistent with glucagon receptor activation stimulating sympathetic tone.

Neither compound has shown the serious safety signals (pancreatitis, thyroid tumors) that shadowed early GLP-1 agonist development, but long-term post-marketing surveillance data is still limited for both.

Dosing and practical considerations

[[Cagrilintide|12]] is administered as a once-weekly subcutaneous injection. Clinical trials used doses up to 4.5 mg. For research purposes, typ...