Amylin vs GLP-1 vs GIP vs Glucagon: What Does Each Pathway Actually Do?

The newest generation of metabolic peptides can sound confusing because many of them target several hormone pathways at the same time.

GLP-1.

GIP.

Glucagon.

Amylin.

These names now appear repeatedly in discussions around compounds such as:

• semaglutide
• tirzepatide
• retatrutide
• cagrilintide
• petrelintide
• eloralintide
• CagriSema
• zenagamtide
• survodutide
• mazdutide

But these pathways are not interchangeable.

Each hormone performs a different job within the body’s system for regulating food intake, blood glucose and energy balance.

Understanding those differences makes it much easier to understand why researchers are now combining them.

A major 2026 review in Nature Reviews Drug Discovery describes GLP-1, GIP, glucagon and amylin as central components of the emerging multi-receptor approach to obesity pharmacology. (Nature⁠)

The Simple Version

Before getting into the biology, the four pathways can be simplified like this:

GLP-1
Primarily helps regulate appetite, satiety, glucose and gastric emptying.

GIP
Primarily contributes to insulin signalling and nutrient handling after meals.

Glucagon
Helps regulate energy availability and has important effects on the liver, fat metabolism and energy expenditure.

Amylin
Helps signal meal completion, fullness and reduced food intake.

That is deliberately simplified.

In reality, all four interact with numerous tissues and neural pathways.

What Is GLP-1?

GLP-1 stands for glucagon-like peptide-1.

It is produced mainly by specialised intestinal cells after nutrients enter the digestive system.

GLP-1 then communicates with several organs, including:

• pancreas
• stomach
• brain
• cardiovascular system

Its discovery eventually led to one of the biggest changes in modern metabolic medicine.

What Does GLP-1 Do to Appetite?

GLP-1 signalling influences brain regions involved in hunger and satiety.

Activating the GLP-1 receptor can:

• reduce hunger
• increase feelings of fullness
• reduce food intake
• alter food-related reward

These central effects are an important reason GLP-1 receptor agonists can produce substantial body-weight reduction.

What Does GLP-1 Do to Blood Glucose?

GLP-1 stimulates insulin secretion when blood glucose is elevated.

This is known as glucose-dependent insulin secretion.

The glucose-dependent component is important because it means the signal becomes stronger when glucose is high rather than continuously stimulating insulin regardless of glucose concentration.

GLP-1 also suppresses inappropriate glucagon release after meals.

Together, these effects help reduce post-meal glucose excursions.

What Does GLP-1 Do to the Stomach?

GLP-1 can slow gastric emptying.

That means food leaves the stomach more slowly.

This can contribute to:

• prolonged fullness
• slower nutrient absorption
• reduced post-meal glucose spikes

However, the effect on gastric emptying can change with prolonged treatment and varies between different GLP-1 therapies.

Which Drugs Use GLP-1?

GLP-1 appears in many of the best-known metabolic treatments.

Examples include:

Semaglutide
GLP-1 receptor agonist.

Tirzepatide
GIP + GLP-1 agonist.

Retatrutide
GIP + GLP-1 + glucagon agonist.

Survodutide
GLP-1 + glucagon agonist.

CagriSema
GLP-1 through semaglutide plus amylin-related signalling through cagrilintide.

The 2026 research pipeline increasingly uses GLP-1 as a foundation onto which additional hormone activity is added. (Nature⁠)

What Is GIP?

GIP stands for glucose-dependent insulinotropic polypeptide.

It is another incretin hormone released from the intestine after food intake.

Like GLP-1, GIP can increase insulin secretion in response to glucose.

But GIP has additional effects on tissues involved in nutrient storage and metabolism.

What Does GIP Actually Do?

GIP signalling has been associated with:

• insulin secretion
• nutrient handling
• adipose-tissue biology
• lipid metabolism
• communication between the gut and brain

Its role in obesity is particularly interesting because GIP biology initially appeared contradictory.

Historically, researchers questioned whether stimulating GIP might promote fat storage.

Yet combining GIP with GLP-1 has produced highly effective metabolic therapies.

Why Does Tirzepatide Activate GIP?

Tirzepatide demonstrated that GIP agonism can complement GLP-1 receptor activation.

The exact reasons for the additional weight effect are still being investigated.

Possible mechanisms include effects on:

• brain appetite circuits
• insulin sensitivity
• adipose tissue
• tolerability of GLP-1 signalling

The important point is that GIP does not simply duplicate GLP-1.

The combination creates a different receptor-signalling profile.

But Doesn’t MariTide Block GIP?

Yes — and this is one of the most fascinating aspects of the field.

Tirzepatide activates the GIP receptor.

MariTide blocks it while activating GLP-1.

Yet both strategies can produce substantial weight reduction.

This apparent contradiction illustrates how complicated receptor biology can be.

The effects of GIP may depend on:

• tissue
• duration of signalling
• receptor desensitisation
• interaction with GLP-1
• central nervous system effects

So the simplified idea that GIP is either universally “good” or “bad” is unlikely to be correct.

What Is Glucagon?

Glucagon is another peptide hormone produced by the pancreas.

Most people know glucagon because it raises blood glucose.

When glucose falls, glucagon signals the liver to release stored energy.

But glucagon has many additional metabolic effects.

What Does Glucagon Do in the Liver?

The liver is one of glucagon’s major targets.

Glucagon signalling influences:

• glycogen breakdown
• glucose production
• lipid metabolism
• fatty-acid oxidation
• amino-acid metabolism

This is one reason glucagon receptor agonism is being investigated in metabolic liver disease as well as obesity.

Why Would an Obesity Drug Activate a Hormone That Raises Glucose?

This seems counterintuitive.

If glucagon raises glucose, why would researchers deliberately activate it?

Because glucagon can also:

• increase energy expenditure
• increase fat oxidation
• affect liver fat
• influence thermogenesis

The strategy is therefore to combine glucagon with a hormone such as GLP-1 that helps control glucose.

The GLP-1 component may offset glucagon’s glucose-raising tendency while preserving some of its potentially useful metabolic effects.

Which Peptides Use Glucagon Signalling?

Several important emerging compounds do.

Survodutide
GLP-1 + glucagon.

Mazdutide
GLP-1 + glucagon.

Pemvidutide
GLP-1 + glucagon.

Retatrutide
GIP + GLP-1 + glucagon.

Efocipegtrutide
GIP + GLP-1 + glucagon.

This pathway is becoming especially important in obesity and liver-disease research.

What Is Amylin?

Amylin is a peptide hormone released from pancreatic beta cells alongside insulin.

Whereas insulin is heavily involved in controlling glucose movement and storage, amylin acts partly as a meal-related satiety signal.

It helps regulate how much and how quickly food is consumed.

What Does Amylin Do?

Amylin contributes to:

• increased satiety
• reduced meal size
• meal termination
• slower gastric emptying
• suppression of post-meal glucagon
• communication between the gut, pancreas and brain

That makes it an obvious candidate for obesity research.

How Is Amylin Different From GLP-1?

There is overlap.

Both can:

• reduce food intake
• increase satiety
• slow gastric emptying
• influence glucagon

But they communicate through different receptor systems and different neural pathways.

This is why combining the two may produce effects that are greater than simply increasing one pathway alone.

Which New Peptides Target Amylin?

Amylin has become one of the fastest-growing areas in peptide research.

Examples include:

Cagrilintide
Long-acting amylin analogue.

Petrelintide
Long-acting amylin analogue.

Eloralintide
Selective amylin receptor agonist.

Zenagamtide
One molecule combining amylin-related and GLP-1 activity.

CagriSema
Cagrilintide + semaglutide.

A 2026 review highlighted cagrilintide-based CagriSema, eloralintide and zenagamtide among the leading next-generation amylin programmes. (PubMed⁠)

Why Do Researchers Keep Combining These Hormones?

Because body weight is not controlled by one pathway.

Eating behaviour involves multiple signals relating to:

• hunger
• fullness
• meal size
• food reward
• blood glucose
• nutrient availability
• energy expenditure
• fat storage
• liver metabolism

A single receptor cannot necessarily address all of those systems.

Multi-receptor therapies attempt to influence several simultaneously.

A 2026 review of GLP-1 combination strategies describes dual, triple and amylin-containing approaches as a major frontier because they can combine regulation of appetite, energy metabolism and lipid biology. (PubMed⁠)

How Does Semaglutide Fit Into This?

Semaglutide is the simplest comparison.

It primarily activates:

GLP-1

That gives researchers a baseline for understanding what happens when additional pathways are added.

How Does Tirzepatide Fit In?

Tirzepatide activates:

GIP + GLP-1

The additional GIP activity differentiates it from conventional GLP-1 monotherapy.

How Does Retatrutide Fit In?

Retatrutide adds a third receptor:

GIP + GLP-1 + glucagon

This means it attempts to influence both:

• energy intake
• energy expenditure

within one engineered peptide.

How Does CagriSema Fit In?

CagriSema approaches the problem differently.

Rather than adding GIP or glucagon to GLP-1, it combines:

GLP-1 + amylin

through semaglutide and cagrilintide.

This primarily expands the satiety and meal-regulation side of the system.

What About Cagri + Reta?

This is where the current research frontier becomes particularly interesting.

Retatrutide already provides:

• GIP
• GLP-1
• glucagon

Cagrilintide adds amylin-related signalling.

That creates a much broader receptor network.

The 2026 preclinical Cagri + Reta research is therefore effectively asking:

What happens when appetite, incretin, glucagon and amylin signalling are all manipulated at the same time?

This remains preclinical rather than established human therapy.

Which Pathway Mainly Controls Appetite?

There is no single appetite receptor.

But GLP-1 and amylin are particularly important in the current drug-development landscape.

GLP-1 has strong effects on appetite and food intake.

Amylin appears especially important for:

• meal termination
• satiety
• meal size

Combining those systems is therefore scientifically attractive.

Which Pathway Mainly Affects Energy Expenditure?

Glucagon is currently the most prominent of these four in relation to energy expenditure.

That is one reason retatrutide and GLP-1/glucagon dual agonists have generated so much interest.

But energy expenditure is extremely complex and cannot be reduced to a single hormone.

Which Pathway Mainly Controls Insulin?

Both GLP-1 and GIP have important insulinotropic effects.

That is why they are collectively referred to as incretin hormones.

Their insulin-stimulating effects are strongly dependent on glucose levels.

Which Pathway Mainly Affects the Liver?

Glucagon has particularly important direct effects on liver metabolism.

GLP-1-based therapies can also improve liver health indirectly through weight reduction and metabolic improvements.

This distinction is one reason glucagon-containing peptides are being investigated specifically for MASH and liver fat.

Which Pathway Is “Best”?

There probably isn’t one.

The growing clinical evidence suggests that different combinations may be useful for different purposes.

One combination may be optimised for:

• maximum weight reduction

another for:

• diabetes control

another for:

• liver disease

another for:

• long-term appetite control

A 2026 review of receptor-network pharmacology argues that treatments increasingly need to be understood according to their outcome evidence and biological profile, rather than assuming one receptor combination is universally superior. (PubMed⁠)

Could Different People Eventually Receive Different Pathway Combinations?

Possibly.

Some people may have particularly strong:

• hunger
• reward-driven eating
• insulin resistance
• metabolic liver dysfunction
• energy-conservation responses

Researchers are beginning to explore whether these biological differences could eventually help determine which pathway combinations work best.

But current evidence is not strong enough to use these profiles routinely to select therapy. (PubMed⁠)

Why Isn’t Maximum Weight Loss the Only Goal?

Because successful metabolic treatment involves more than a number on the scales.

Researchers increasingly need to evaluate:

• fat mass
• lean mass
• cardiovascular outcomes
• kidney outcomes
• liver health
• glucose regulation
• nutritional status
• treatment durability
• quality of life

Some established GLP-1 therapies already have mature cardiovascular or renal outcome evidence, while many newer dual, triple and amylin-based approaches currently have stronger weight-loss data than long-term outcome data. (PubMed⁠)

Could More Receptors Cause More Side Effects?

Potentially.

Each receptor pathway adds another biological effect.

Combining pathways may increase effectiveness.

But it can also increase:

• nausea
• vomiting
• appetite suppression
• gastrointestinal effects
• complexity of dosing
• unpredictable interactions

The aim is therefore not simply to activate the greatest number of receptors possible.

It is to find the optimal receptor balance.

What Does “Receptor Balance” Mean?

Imagine a drug activates GLP-1, GIP and glucagon.

It does not necessarily activate them equally.

One molecule might have:

strong GLP-1 activity,

moderate GIP activity,

and relatively mild glucagon activity.

Another could have the opposite balance.

Those differences can substantially change the drug’s effects.

This is why two compounds targeting the same receptors can behave differently clinically.

The Bigger Picture

The modern metabolic peptide field can be viewed as a progression:

GLP-1

↓

GLP-1 + GIP

↓

GLP-1 + glucagon

↓

GLP-1 + amylin

↓

GLP-1 + GIP + glucagon

↓

multi-pathway combinations involving amylin

That evolution is transforming obesity pharmacology.

A 2026 systematic review of 38 randomised trials involving more than 25,000 participants found increasingly large weight reductions with newer multiagonists, including retatrutide and amylin/GLP-1 approaches. (PubMed⁠)

The Bottom Line

GLP-1, GIP, glucagon and amylin are four different metabolic hormone pathways.

They overlap, but each contributes something distinct.

GLP-1
Primarily contributes to appetite reduction, satiety, glucose regulation and gastric emptying.

GIP
Contributes to insulin signalling, nutrient handling and metabolic regulation.

Glucagon
Has particularly important effects on liver metabolism, energy availability, fat oxidation and energy expenditure.

Amylin
Contributes strongly to meal termination, fullness, reduced food intake and post-meal regulation.

The current revolution in peptide research comes from combining these signals rather than treating them as isolated systems.

That is why the field has progressed from single GLP-1 drugs to dual agonists, triple agonists and now experimental combinations involving four or more pathways. (Nature⁠)

The goal is not simply to activate as many receptors as possible.

It is to identify which combination produces the best balance of appetite control, metabolic health, energy regulation, safety and long-term outcomes.

That is the central question behind much of the next generation of peptide research.

This article is for research and educational purposes only. Several compounds and combinations discussed remain investigational, and biological mechanisms should not be interpreted as evidence that untested combinations are safe or effective.