Best Peptides for Weight Loss Research: GLP-1s, MOTS-c, 5-Amino-1MQ and More

No area of peptide science has exploded like weight loss research. In the space of a few years, peptides that copy the gut’s own fullness hormones went from specialist diabetes medicines to some of the most talked-about drugs in the world, and interest in every other peptide with a link to metabolism rose with them. Researchers now study peptides that act on appetite, on how cells burn fuel, on how fat is stored and on the hormone systems that shape body composition.

But the compounds involved are very different from one another, and “best” depends entirely on which part of metabolism a study is trying to understand. This guide explains the main classes of peptides and related compounds in weight loss and metabolic research, what the key studies found and how each is thought to work, so you can match the right tool to the right question. It is an overview of research findings, not medical or weight loss advice. Research compounds mentioned are supplied by Crown Peptides for laboratory research use only.

How Body Weight Is Actually Regulated

Energy balance

At the simplest level, body weight reflects the balance between energy taken in as food and energy used by the body. But that balance is not controlled by willpower alone. It is regulated by a complex network of hormones and brain circuits that monitor energy stores and adjust appetite and energy use to defend them.

The brain as the control centre

The hypothalamus, a small region at the base of the brain, integrates signals from fat tissue, the gut, the pancreas and the rest of the body to regulate hunger and fullness. Leptin, made by fat cells, reports on long-term energy stores. Ghrelin, from the stomach, signals hunger. GLP-1, PYY and other gut hormones signal fullness after meals. Insulin reports on blood sugar.

Fat tissue is an active organ

Fat tissue is not just a passive store of energy, as was once widely assumed by scientists. It releases hormones, responds to signals from the brain and changes its behaviour in obesity. How fat cells take up, store and release fat, and how they use energy, are major research questions.

Cellular energy

Inside every cell, mitochondria burn fuel to produce energy. How efficiently they do so, and which fuel they choose, influences overall energy use. That is why mitochondrial and cellular energy research has become part of the weight loss picture.

A Short History of Weight Loss Research

The discovery of leptin

Modern obesity science began in 1994, when Jeffrey Friedman’s laboratory at Rockefeller University identified leptin, a hormone made by fat cells that tells the brain how much energy the body has stored. Mice lacking leptin became enormously obese, and giving them leptin reversed it. The discovery proved that body weight is regulated by hormones, not simply by willpower. But most people with obesity turned out to have high leptin levels and to be resistant to its effects, so leptin itself did not become a general treatment.

Decades of disappointment

For years, weight loss medicines were a story of modest results and safety setbacks. Several were withdrawn after problems emerged, including the fenfluramine combination linked to heart valve damage in the 1990s and rimonabant, withdrawn in Europe in 2008 because of psychiatric side effects. These episodes made researchers and regulators cautious, and they are a reminder of why large trials matter.

The GLP-1 era

The turning point came with GLP-1. Liraglutide showed meaningful weight effects in the 2010s, and semaglutide’s STEP 1 results in 2021 changed the field. For the first time, a peptide produced average weight reductions of around 15% in a large, rigorous trial. Tirzepatide and retatrutide have since pushed the figures further. Weight loss research has never been busier.

The Appetite Hormones in More Detail

Ghrelin

Ghrelin, made mainly in the stomach, rises before meals and signals hunger. It is the only well-established circulating hunger hormone, and it also stimulates growth hormone release, which is why growth hormone releasing peptides that act on its receptor often increase appetite.

GLP-1 and PYY

GLP-1 and peptide YY are released by the lower gut after eating and signal fullness to the brain. They also slow stomach emptying.

Leptin

Leptin reports long-term fat stores to the brain. In obesity, the brain becomes less responsive to it.

Insulin

Insulin, released by the pancreas when blood sugar rises, also acts on the brain to reduce appetite and promotes fat storage in fat tissue.

Why this matters

Each of these hormones is a potential research target, and the most successful weight loss peptides so far work by mimicking fullness signals. Understanding the whole network helps explain why combining signals, as tirzepatide and retatrutide do, can produce larger effects.

Class 1: The Incretin Peptides

The most powerful and best-studied peptides in this field are those that act on incretin hormone receptors, especially GLP-1.

Semaglutide

Semaglutide, a long-acting analogue of GLP-1, is the best-known. In the STEP 1 trial, published in the New England Journal of Medicine in 2021, 1,961 adults with overweight or obesity received weekly semaglutide or placebo for 68 weeks alongside lifestyle support (PMID: 33567185). The mean change in body weight was -14.9% with semaglutide and -2.4% with placebo. Gastrointestinal side effects were the most common adverse events. Our article is Ozempic a peptide tells its story.

Tirzepatide

Tirzepatide acts on both the GLP-1 receptor and the receptor for GIP, the other main incretin hormone. In the SURMOUNT-1 trial of 2,539 adults with obesity, published in 2022, it produced mean weight reductions of 15% to 21% over 72 weeks depending on strength, compared with 3.1% with placebo (PMID: 35658024).

Retatrutide

Retatrutide adds a third target, the glucagon receptor. In a 2023 phase 2 trial in 338 adults with obesity, it produced mean weight reductions of up to 24.2% at 48 weeks in the highest-strength group, compared with 2.1% with placebo (PMID: 37366315). Gastrointestinal effects and dose-dependent increases in heart rate were reported. Our article retatrutide vs tirzepatide compares the two.

Best suited to

Research on appetite regulation, incretin signalling, glucose control and the brain’s role in body weight. Research compounds in this area are grouped in our metabolic research peptides category.

Class 2: Mitochondrial Signalling, MOTS-c

MOTS-c is a 16-amino-acid peptide encoded in the small genome inside mitochondria. In its 2015 discovery paper in Cell Metabolism, Lee, Cohen and colleagues found that MOTS-c activated AMPK, the cell’s energy sensor, and prevented both diet-induced obesity and insulin resistance in mice (PMID: 25738459, PMC4350682). A 2021 study found that a naturally occurring variant of MOTS-c, carried mainly by people of East Asian ancestry, was associated with type 2 diabetes in less active men, and that the variant lacked the normal version’s effects on weight and glucose in mice (PMID: 33468709, PMC7880332).

Best suited to

Research on cellular energy sensing, insulin sensitivity, exercise-like signalling and the metabolic role of mitochondria. See our MOTS-c guide.

Class 3: NNMT Inhibition, 5-Amino-1MQ

5-Amino-1MQ is a small molecule that blocks the enzyme NNMT, which is more active in the fat tissue of obese animals. A 2014 study in Nature by Kraus, Kahn and colleagues showed that reducing NNMT in fat and liver protected mice against diet-induced obesity by increasing energy expenditure (PMID: 24717514, PMC4107212). In a 2018 study in Biochemical Pharmacology, a methylquinolinium NNMT inhibitor reduced body weight and fat mass in diet-induced obese mice without reducing food intake (PMID: 29155147, PMC5826726).

Best suited to

Research on fat cell energy use, NAD+ and methylation, and weight change independent of appetite. See our 5-Amino-1MQ guide.

Class 4: The Growth Hormone Axis

Tesamorelin and visceral fat

Growth hormone influences how the body stores and uses fat, particularly the deep abdominal, or visceral, fat that surrounds the organs. In a 2007 study in the New England Journal of Medicine, Falutz and colleagues found that Tesamorelin, a GHRH analogue, reduced visceral abdominal fat in people with HIV-associated fat accumulation (PMID: 18057338). Tesamorelin was later approved in the United States for that specific condition.

AOD-9604

AOD-9604 is a modified fragment from the end of the growth hormone molecule, designed to retain growth hormone’s effects on fat metabolism without its effects on growth. A 2004 review in Current Opinion in Investigational Drugs summarised its development as an anti-obesity compound (PMID: 15134286). Its later clinical trials did not show sufficient effect on weight for it to be developed further as an obesity medicine, which is itself useful knowledge for researchers.

Best suited to

Research on visceral fat, growth hormone’s metabolic effects and fat breakdown. See AOD-9604: the fragment of growth hormone built to do just one of its jobs.

Class 5: Fuel Handling and Cellular Energy

L-Carnitine

L-Carnitine carries fatty acids into mitochondria so they can be burned for energy, making it essential for fat metabolism. See L-Carnitine: the molecule that decides which fuel your mitochondria burn.

NAD+

NAD+ is central to energy metabolism and the sirtuin enzymes that respond to nutrient availability. Research compounds such as 5-Amino-1MQ act partly through the NAD+ supply.

SS-31

SS-31 targets the inner mitochondrial membrane and is studied for mitochondrial efficiency.

How the Classes Fit Together

It can help to picture the classes in this guide as acting at different levels of the same system. The incretin peptides act on the signals that travel from the gut to the brain and pancreas, changing how much food is eaten and how blood sugar is handled. The growth hormone axis compounds act on a hormone system that shapes where fat is stored and how much lean tissue is kept. MOTS-c and 5-Amino-1MQ act inside cells, on the machinery that senses energy and decides how much fuel to burn. L-Carnitine, NAD+ and SS-31 act on the mitochondria themselves. A study that combines measures across these levels, such as appetite, hormones, body composition and cellular energy use, can reveal how a single compound ripples through the whole system, or how two compounds acting at different levels interact. That layered view is one of the most productive ways to think about metabolic research.

The Metabolic Research Bundle

For researchers studying metabolism as a system, the Metabolic Research Bundle brings metabolic compounds together in separate vials. Our article three peptides, one metabolic pathway explains the thinking behind it.

Matching the Compound to the Question

• Appetite and incretin signalling: GLP-1-class compounds in the metabolic research category.
• Cellular energy sensing and insulin sensitivity: MOTS-c.
• Fat cell energy use independent of appetite: 5-Amino-1MQ.
• Visceral fat and the growth hormone axis: Tesamorelin.
• Fat breakdown without growth effects: AOD-9604.
• Fatty acid transport into mitochondria: L-Carnitine.
• NAD+ and mitochondrial efficiency: NAD+ and SS-31.

Why Weight Loss Is So Hard to Maintain

One of the most important findings in obesity research is that the body resists weight loss. When energy stores fall, leptin drops, hunger hormones rise, fullness signals weaken and the body becomes more efficient at using energy, a process called metabolic adaptation. This helps explain why weight is often regained after a diet, and why, in follow-up of the semaglutide trials, much of the weight lost was regained after treatment stopped. For researchers, it means that studying how weight is maintained is just as important as studying how it is lost.

Muscle and Weight Loss

When body weight falls, some of the loss is usually lean mass, including muscle, not just fat. How much lean mass is lost, and whether it can be protected, has become a major question in the GLP-1 era. That is why body composition measurement matters so much in weight loss research, and why interest in compounds that support muscle, such as those studied in the growth hormone axis, has grown alongside interest in weight loss. Our guide to best peptides for muscle research covers that side.

Brown Fat and Energy Burning

Not all fat stores energy. Brown fat, found in small amounts in adults, burns fuel to produce heat through a protein called UCP1, which makes mitochondria deliberately inefficient. Research has shown that brown fat activity varies between people and can be increased by cold exposure. Compounds that influence mitochondrial function and energy use, such as MOTS-c and those acting on the NAD+ system, are of interest partly because of how they might interact with energy-burning processes like this. It is an active area of metabolic research.

The Liver: An Overlooked Player

The liver is central to metabolism. It stores and releases sugar, makes and exports fat, and processes nutrients arriving from the gut. In obesity, fat often builds up in the liver itself, a condition now called metabolic dysfunction-associated steatotic liver disease. The glucagon receptor, one of retatrutide’s three targets, acts mainly in the liver, increasing fat breakdown there, and a 2024 trial reported large reductions in liver fat with retatrutide (PMID: 38858523, PMC11271400). NNMT, the target of 5-Amino-1MQ, is also highly active in the liver. Measuring liver fat and liver markers adds an important dimension to weight loss research.

Comparing Compounds Fairly

Headlines often compare weight loss compounds by their headline percentage, but fair comparison is harder than it looks. Trials differ in the people enrolled, their starting weight, whether they had diabetes, the length of the trial and the lifestyle support provided. People with type 2 diabetes, for example, tend to lose less weight with the same compound than people without it. The fairest comparisons come from head-to-head trials in the same population. In laboratory research, the same principle applies: compounds should be compared in the same model, with the same diet, housing and measurements.

Sex Differences in Metabolic Research

Males and females often respond differently in metabolic studies. The MOTS-c variant study found effects in men but not women, in both people and mice, and hormonal differences influence fat distribution, appetite and energy use. Including both sexes and analysing them separately has become standard good practice in metabolic research, and it often reveals effects that would otherwise be hidden.

Designing Metabolic Research

Always measure food intake

The single most important control in weight research is food intake. A compound that reduces weight may do so by reducing appetite, by increasing energy use or both, and only by measuring intake can those be separated. The 2018 NNMT inhibitor study was notable precisely because treated mice lost weight without eating less.

Pair-feeding

In pair-feeding designs, control animals are given exactly the amount of food the treated animals chose to eat. Any remaining difference in weight must then come from energy use rather than appetite.

Measure body composition, not just weight

Weight alone does not show whether fat, muscle or water changed. Techniques such as DXA scanning and MRI measure fat and lean mass separately, and can distinguish visceral fat from fat under the skin.

Measure energy expenditure

Indirect calorimetry measures oxygen use and carbon dioxide production to calculate how much energy an animal burns and which fuels it uses.

Use the right model

Diet-induced obese mice, fed a high-fat diet, are the standard model for common obesity. Genetic models, such as mice lacking leptin, test specific pathways.

Common Pitfalls in Weight Loss Research

Ignoring food intake

Without measuring intake, it is impossible to know whether weight change reflects appetite or energy use.

Measuring weight alone

Weight changes can reflect water, muscle or fat. Body composition measures are needed to know what actually changed.

Short studies

Short studies can miss metabolic adaptation and weight regain.

Mouse housing temperature

Standard laboratory temperatures are cool for mice, forcing them to burn extra energy to stay warm, which can affect metabolic results. Many researchers now study mice at warmer temperatures closer to their comfort zone to make findings more relevant.

The Technical Breakdown: Metabolic Signalling Pathways

Incretin receptors

The GLP-1 and GIP receptors are class B G protein-coupled receptors that raise cyclic AMP in pancreatic beta cells, amplifying glucose-dependent insulin release. GLP-1 receptors in the brain influence appetite. The glucagon receptor, targeted by retatrutide, increases energy expenditure and fat breakdown in the liver.

AMPK

AMPK is activated when a cell’s energy runs low. It increases glucose uptake and fat burning and reduces fat and protein synthesis. MOTS-c activates it, as do exercise and calorie restriction.

NNMT and futile cycles

Reducing NNMT raises NAD+ and the methyl donor SAM in fat cells. The Harvard study found that extra SAM increased histone methylation and switched on genes that speed up polyamine cycling, an energy-consuming process, which increased fat cell energy use.

Growth hormone and fat

Growth hormone promotes the breakdown of stored fat, particularly visceral fat, while supporting lean tissue through IGF-1. GHRH analogues such as tesamorelin increase the body’s own growth hormone release, preserving its natural pulsatile pattern.

A Word on Compliance and Quality

Weight loss is one of the areas most affected by unlicensed and counterfeit products. Regulators have warned repeatedly about fake GLP-1 products, and studies of falsified peptide products have found very low purity and toxic metal contamination (PMID: 30029448). Research compounds are not medicines and are not supplied for weight loss in people.

Every research compound supplied by Crown Peptides comes with a batch-specific certificate of analysis showing HPLC purity and mass spectrometry identity. Published certificates are on our Lab Reports page, and our guides to peptide testing and how to tell if peptides are real explain the methods.

Related Reading

For background, read NAD+ vs MOTS-c, SS-31 vs MOTS-c, best peptides for longevity research and are peptides safe.

Weight Loss Research Questions, Answered

What are the most studied peptides for weight loss?

The incretin-based peptides, semaglutide, tirzepatide and retatrutide, have by far the strongest evidence, from large randomised trials. Research compounds such as MOTS-c and 5-Amino-1MQ have been studied mainly in animals.

How do GLP-1 peptides reduce weight?

Mainly by reducing appetite through receptors in the brain and slowing stomach emptying, which prolongs fullness.

Do any compounds reduce weight without reducing appetite?

In mouse research, an NNMT inhibitor from the same family as 5-Amino-1MQ reduced weight and fat mass without reducing food intake, pointing to increased energy use.

What is the difference between semaglutide, tirzepatide and retatrutide?

Semaglutide acts on the GLP-1 receptor alone. Tirzepatide acts on GLP-1 and GIP receptors. Retatrutide acts on GLP-1, GIP and glucagon receptors. In their respective trials, adding receptors was associated with larger average weight reductions.

Why is food intake so important in weight research?

Because weight change can come from eating less, burning more or both, and only by measuring intake can researchers tell which. Pair-feeding designs go further, giving control animals the same amount of food as treated ones.

Why do GLP-1 compounds cause nausea?

Mainly because they slow stomach emptying and act on brain regions involved in nausea. In the large trials, these effects were most common early on and as the amount was increased, and tended to ease over time.

Do weight loss peptides affect muscle?

Weight loss generally includes some loss of lean mass as well as fat, which is why body composition is measured carefully in modern trials and why muscle preservation has become an important research question.

Is there a best peptide for weight loss research?

It depends on the question. Incretin-class compounds suit appetite and glucose research, MOTS-c suits cellular energy research, 5-Amino-1MQ suits fat cell energy use, and tesamorelin suits visceral fat and growth hormone research.

Why is weight often regained?

Because the body adapts to lower energy stores by increasing hunger and reducing energy use, and because the effects of appetite-modifying compounds depend on their continued presence.

What is brown fat?

A type of fat that burns fuel to produce heat rather than storing it, using the protein UCP1 in its mitochondria.

What is visceral fat?

Fat stored deep in the abdomen around the organs. It is more metabolically active than fat under the skin and is a focus of growth hormone axis research, including tesamorelin studies.

Are research peptides for weight loss legal in the UK?

The research compounds in this guide are not controlled drugs, but they are not licensed medicines and are not supplied for weight loss in people. See are peptides legal in the UK.

Many Routes Into One of Biology’s Biggest Questions

Body weight is shaped by the brain, the gut, the pancreas, fat tissue and the mitochondria inside every cell, and weight loss research now has tools for each. Incretin peptides act on appetite and blood sugar with results proven in large trials. MOTS-c and 5-Amino-1MQ probe cellular energy. Tesamorelin and AOD-9604 explore the growth hormone axis. L-Carnitine, NAD+ and SS-31 examine how fuel is burned. The best compound is simply the one that fits the question being asked, and the best studies measure food intake, body composition and energy use together rather than relying on weight alone.

Explore the Crown Peptides metabolic research range, supplied for laboratory research, every batch HPLC and mass spectrometry verified and dispatched from the UK.