Peptides for Weight Loss Research: Evaluating GLP-1 and GIP Pathways 

[Photo by Getty Images via Canva].

Weight loss and the management of it are important areas of focus in metabolic research. It’s well known that nutrition, sleep quality, genetics, and level of physical activity all affect weight, but there’s been an increase in interest in peptides for weight loss and their role in the balance of energy.

Some peptides have migrated from lab research to approved therapies; some remain investigational. Research today focuses on how they interact with the metabolic pathways associated with blood sugar regulation and body weight, as well as the biology of fat cells.

We’ll examine what the research says about peptides for weight loss and look into the current scientific literature.

Note: These peptides are only manufactured for research.  

What Are Peptides?

Peptides are short chains of amino acids that act as messengers in the body. They are smaller than proteins and regulate normal bodily functions, helping cells communicate.¹

These pathways help control weight, which is why researchers are investigating if certain peptides can influence metabolic functions associated with excess weight. Peptides interact with different receptors in the body, and the outcome depends on how those receptors respond.²

Peptides Investigated in Metabolic Research

Peptides don’t work via a single mechanism; their actions change depending on the molecule. For example, some peptides may help reduce food intake, while others might influence endocrine signals or lipid (fat) metabolism.3 Researchers claim they could affect multiple pathways associated with:

• Regulating appetite
• Gastric (stomach) emptying
• Energy intake
• Changes in fat tissue
• How insulin works in the body
• Glucose and lipid metabolism

Fat-Targeting Peptides: AOD-9604 and Tesamorelin

AOD-9604 and Tesamorelin are peptides that often come up in metabolic research, although they work differently.

AOD-9604

LYOPHILIZED POWDER

AOD-9604

For research use only

Read More

Researchers have studied AOD-9604, a segment of human growth hormone, to determine if it has an influence on metabolism.

Early research suggests that AOD-9604 may influence:

• Lipolysis (the breakdown of fat)
• Inhibition of lipogenesis (the storage of fat)
• Adipocyte metabolism (how fat cells break down and store fat)

These studies show that AOD-9604 has a limited effect on fat metabolism. Human clinical trials to date haven’t shown much of an effect on weight loss, and it doesn’t cause much change in blood sugar regulation either.⁴

Tesamorelin

Tesamorelin is a synthetic (lab-made) peptide, or growth hormone-releasing hormone (GHRH), that encourages the body to produce its own growth hormone (endogenous growth hormone). It doesn’t act directly on fat cells, but it activates the hormones involved in body composition.⁵

Clinical studies have mostly looked at Tesamorelin’s effects on HIV-associated lipodystrophy (abnormal fat distribution) in adults and found that it lowered visceral adipose tissue (fat around the organs) and preserved lean tissue. It is not an approved weight-loss treatment, however, and current research suggests it is mainly effective at reducing visceral fat rather than total body weight.⁶

GLP-1 Agonists: Appetite Regulation and Blood Sugar Control

GLP-1 agonists mimic the body’s own GLP-1 hormone. Out of all the peptide-based therapies, the GLP-1 receptor agonists have the strongest clinical evidence for weight management because they mimic glucagon-like peptide-1 (GLP-1), the natural hormone that is released after eating, and act on the receptors in the brain, pancreas, cardiovascular system, and gastrointestinal tract.⁷

Studies show that this type of medication may:

• Increase the feeling of fullness
• Reduce calorie intake
• Reduce appetite by activating the central nervous system
• Delay gastric emptying
• Improve blood sugar control

During controlled trials, studies of the GLP-1 peptides showed they contributed to notable weight loss when they were combined with other lifestyle changes, such as consuming approximately 500 fewer calories per day and doing at least 150 minutes of physical exercise every week, throughout the 68-week study.⁸

Semaglutide

Semaglutide is known as a long-acting compound, which means it’s effective for a longer time, and it also acts like the GLP-1 hormone the body naturally produces.

In the STEP clinical trial program, after 68 weeks, Semaglutide resulted in an average reduction in body weight of 14.9%, compared with the placebo group’s 2.4%. Researchers noted that these effects were mainly due to lowered appetite and energy intake, rather than increased energy expenditure.⁸

Tirzepatide

Tirzepatide is a newer peptide therapy that activates both:

• Glucose-dependent insulinotropic polypeptide (GIP) (a hormone involved in blood sugar and appetite regulation) receptors
• GLP-1 receptors

This system is interesting to researchers because of its ability to influence multiple metabolic pathways at the same time.

The precise contribution of GIP receptors is still being investigated. However, current clinical trials have shown Tirzepatide may contribute to a greater reduction in weight than GLP-1 on its own.9 They’ve also shown improvements in:

• Insulin sensitivity
• Appetite regulation
• Glycemic control (blood sugar control)

Tirzepatide has been found to produce even larger reductions in clinical subjects. In a 72-week trial, subjects receiving tirzepatide experienced, on average, weight reductions of 15% to 20.9%, depending on the dose, compared with 3.1% in the placebo group.¹⁰

(These figures are not guaranteed; they are averages from controlled clinical subjects under trial conditions.)

Safety of Peptides

The health risks of peptides depend on the dose used and the population studied, as well as what the peptides are intended for and the molecule itself. Semaglutide and Tirzepatide have been studied in large trials8, but there’s less clinical evidence to support significant weight loss with AOD-960411 and GHRPs.

The most common side effects in GLP-1 and dual GIP/GLP-1 studies were gastrointestinal, including nausea, abdominal discomfort, diarrhea, vomiting, and constipation.¹¹

Tesamorelin has a distinct safety profile because it operates through growth hormone-releasing hormone pathways. Most of its side effects primarily stem from a constant increase in growth hormone and Insulin-like Growth Factor 1 (IGF-1). Higher growth hormone levels interfere with how insulin works, which can result in temporary peaks in insulin levels and blood sugar. Tesamorelin may also cause local skin reactions such as swelling, redness, and inflammation at the administration site. In animal studies, at higher doses, an increase in IGF-1 has shown changes such as bone growth, tissue enlargement, and swelling in organs.

Published research has mostly focused on the visceral fat reduction lipodystrophy associated with HIV and not on overall weight loss.¹²

Exclusion Criteria in Clinical Studies

In GLP-1 research, subjects with the following conditions are commonly excluded8,¹⁰:

• A history of pancreatitis
• Certain thyroid cancers
• Severe gastrointestinal diseases
• Complex endocrine conditions

Handling, Storage, and Research Quality

Each batch of research peptides must be handled and stored correctly in accordance with quality control procedures, as the outcomes depend on the quality of the evaluation materials. Temperature and light exposure can affect the peptides, and documents, such as Certificates of Analysis (COAs), allow the testing to be reproduced at different laboratories.

Testing for purity, checking batches, and following protocols lead to more reliable results.

To learn more about testing and handling, read this guide on achieving and verifying peptide purity.

[Photo by Getty Images, via Canva].

FAQs

Which Peptide Classes Have the Strongest Evidence for Appetite Control?

The GLP-1 receptor agonists have been the most researched in terms of their effect on appetite regulation compared to peptides studied for lipolysis (fat breakdown) or growth hormone triggers. Because they interact with the central nervous system pathways involved in food intake and satiety (fullness), they are an important focus of metabolic research.¹³

How Do Research Peptides Differ From Approved Pharmaceutical Products?

Research peptides, such as those supplied by Licensed Peptides, are intended only for lab use and not as weight-loss peptide medications for clinical use, diagnosis, disease prevention, or treatment (e.g., high blood pressure).

Some compounds share the same peptide sequence as approved medications, but they are still not pharmaceutical products.

Conclusion

As peptide studies evolve, researchers are gaining a better understanding of how different pathways change energy regulation and metabolism. The findings do vary considerably from molecule to molecule, which reiterates the importance of interpreting results through peer-reviewed research.

To sum up, the research on “fat loss peptides” suggests they may affect the gastric emptying rate, blood sugar levels, fat metabolism and breakdown, and appetite; GLP-1 and dual GIP/GLP-1 receptor agonists (specifically Semaglutide and Tirzepatide) show the strongest clinical evidence to date.

The other peptides, AOD-9604, Tesamorelin, and GHRPs, need more careful interpretation, as some show metabolic effects in certain subjects but lack comparable evidence of weight loss.

In quality studies, diet, baseline metabolic health, activity levels, and monitoring procedures are carefully controlled and tracked. This ensures researchers can determine whether subjects lose fat or experience a reduction in body mass, and whether it results from the molecule under study or from uncontrolled external factors.

References

1. Kastin AJ, ed. Handbook of Biologically Active Peptides. 2nd ed. Academic Press; 2013.
2. Murphy KG, Bloom SR. Gut hormones and the regulation of energy homeostasis. Nature. 2006;444(7121):854-859.
3. Bailey CJ, Flatt PR, Conlon JM. Recent advances in peptide-based therapies for obesity and type 2 diabetes. Biomed Pharmacother. 2024;171:116124.
4. Ng FM, Sun J, Sharma L, Libinaka R, Jiang WJ, Gianello R. Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone. Horm Res Paediatr. 2000;53(6):274-278.
5. Stanley TL, Feldpausch MN, Oh J, et al. Effect of tesamorelin on visceral fat and liver fat in HIV-infected patients with abdominal obesity: a randomized clinical trial. JAMA. 2014;312(4):380-389.
6. Falutz J, Allas S, Blot K, et al. Metabolic effects of a growth hormone–releasing factor in patients with HIV. N Engl J Med. 2007;357(23):2359–2370.
7. Müller TD, Clemmensen C, Finan B, DiMarchi RD, Tschöp MH. Peptide-based multi-agonists: a new paradigm in metabolic pharmacology. Pharmacol Rev. 2018;70(4):797-867.
8. Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity. N Engl J Med. 2021;384(11):989-1002.
9. Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as compared with semaglutide for the treatment of obesity. N Engl J Med. 2025;393(1):26-36.
10. Jastreboff AM, Aronne LJ, Ahmad NN, et al; SURMOUNT-1 Investigators. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(3):205–216.
11. Stier H, Vos E, Kenley R. Safety and tolerability of the hexadecapeptide AOD9604 in humans. J Endocrinol Metab. 2013;3(1-2):7-15.
12. Falutz J, Allas S, Blot K, et al. Effects of tesamorelin, a growth hormone-releasing factor, in HIV-infected patients with abdominal fat accumulation: a randomized placebo-controlled trial with a safety extension. J Acquir Immune Defic Syndr. 2010;53(3):311-322.
13. Drucker DJ. Mechanisms of action and therapeutic application of glucagon-like peptide-1. Cell Metab. 2018;27(4):740-756.