This article discusses peptides and their rapidly growing popularity. Videos are circulating on social media that promote injectable research chemicals as a quick fix for weight loss, muscle gain, recovery from injuries, or skin rejuvenation. At least, that’s what influencers and people calling themselves health experts promise.
The purpose of this article is to explain what peptides are, how they work in the body, and why some of them are beneficial as medications but potentially dangerous when used in an unregulated manner. This article is not intended as an advertisement or a user guide, but rather to help people evaluate the claims circulating on social media more critically.
What is a peptide?
A peptide is a compound consisting of two or more amino acids linked together by peptide bonds. Peptides act as messengers in the body, triggering, inhibiting, or regulating various processes.
The most common example is insulin, which signals cells to take glucose from the blood and promote energy storage. This explains why people with type 1 diabetes, who do not produce insulin, need to take it by injection.
Another example is GLP-1, which is the body’s own gut hormone and is released after eating. GLP-1 signals the pancreas to release insulin when blood sugar levels rise, slows stomach emptying, and sends a signal to the brain that the stomach is full. When discussing medications, the focus is usually on GLP-1 receptor agonists, which mimic the effects of this hormone but remain in the body much longer. In this way, they help regulate blood sugar, reduce appetite, and keep you feeling full longer (Müller et al., 2019).
How did the use of peptides as medicines begin?
The use of peptides as medications began with research into the body’s own hormones and signaling molecules. Scientists discovered that peptides send various signals to cells, such as regulating blood sugar, appetite, skin pigmentation, and tissue repair. Since natural peptides break down quickly in the body, they began to be modified in the laboratory to make their effects stronger and longer-lasting.
From GLP-1 to Ozempic
The body’s own GLP-1 breaks down within a few minutes, so it could not be used immediately as a medication; however, in 1992, a similar, longer-acting peptide was discovered in the saliva of the Gila monster (Eng et al., 1992). This led to the development of one of the first GLP-1 medications.
Ozempic itself is not, of course, made from the venom of the Gila monster, but this discovery contributed to the development of the drug.
Ozempic as a Weight-Loss Drug
The drug’s original purpose was to help control blood sugar, but studies showed that people using it also lost a significant amount of weight. By affecting the GLP-1 system, semaglutide reduces hunger, induces a feeling of fullness more quickly, and helps people eat less (Wilding et al., 2021).
Ozempic became particularly well-known in 2022, when celebrities and influencers began talking about the rapid weight loss they achieved with it. Among the general public, the name Ozempic became almost a generic term for all GLP-1 weight-loss medications. High demand even caused a drug shortage at one point, which hurt people who were actually battling diabetes.
Side Effects of Ozempic
Ozempic can cause fairly rapid weight loss. In the process, not only does body fat decrease, but muscle and bone mass may also be affected to some extent (Wilding et al., 2021). The risk of muscle loss is higher if a person eats too little and does not engage in strength training.
A study published in 2024 included 64 adults at increased risk of bone fractures. Over the course of a year, hip bone density decreased by approximately 2.6% and spinal bone density by 2.1% among semaglutide users. At the same time, they lost an average of 9.4% of their body weight (Hansen et al., 2024).
The study did not prove that semaglutide directly damages bones. Bone density may also decrease due to weight loss, as a lighter body places less stress on the bones (Hansen et al., 2024). Additionally, the sample size was very small. It has not yet been proven that Ozempic causes osteoporosis or bone fractures in all users.
The real danger lies in weight loss itself, especially if a person does not consume enough protein to maintain muscle mass. Additionally, eating small meal portions can lead to vitamin deficiencies.
How did peptides become popular among young people and fitness enthusiasts?
Peptides gained visibility among young people following the huge popularity of Ozempic. Influencers began talking more and more about GLP-1 medications, rapid weight loss, and various injectable peptides.
Social media often gives the impression that peptides are a safer version of steroids. In reality, many of them are potent signaling molecules that affect appetite, blood sugar, growth hormone, pigmentation, and tissue growth.
Among young people and fitness enthusiasts, the most commonly discussed peptides are retatrutide, MT2, GHK-Cu, and others.
Retatrutide, or “Reta”
Retatrutide is an experimental weight-loss peptide similar to Ozempic but with a stronger and broader range of effects. While semaglutide affects one hormone receptor, retatrutide affects three at once: the GLP-1, GIP, and glucagon receptors (Jastreboff et al., 2023).
In a 2023 study, participants who received the highest dose lost an average of 24.2% of their body weight over 48 weeks (Jastreboff et al., 2023). As a result, “Reta” quickly went viral on social media even before its official approval.
As of August 2026, retatrutide is not an approved medication. It is still being studied, and the substances sold online do not come from any official medication packaging.
Potential side effects of retatrutide that have been identified include nausea, vomiting, diarrhea, constipation, a very severe loss of appetite, and an increased heart rate. In addition, rapid weight loss may increase the risk of gallstones, malnutrition, and hormonal disorders. Not all effects are yet fully known (Jastreboff et al., 2023).
MT2, or Melanotan II
MT2 is used to darken the skin. It signals pigment cells to produce more melanin. MT2 has become popular because it produces a quick tan without the need for prolonged sun exposure (Dorr et al., 1996).
However, it is not a safe injection. MT2 affects several receptors, which is why it can cause nausea, facial flushing, headaches, and a loss of appetite (Dorr et al., 1996).
Cases of melanoma have also been reported following MT2 use, but it is currently impossible to say with certainty whether the cause was MT2, intense UV radiation, or a combination of both (Hjuler & Lorentzen, 2014).
GHK-Cu, or copper peptide
GHK-Cu is a short peptide found in the human body that binds to and transports copper. Copper is necessary, for example, for enzymes involved in collagen synthesis. When tissue is damaged, GHK-Cu may act as a kind of repair signal. It is important to note that it has a very broad range of effects; it transports copper and influences the activity of numerous cells, enzymes, and genes (Pickart et al., 2015).
GHK-Cu is marketed as a skin rejuvenator, a booster of collagen production, a wound-healing agent, and a hair growth enhancer.
In topical cosmetic products, GHK-Cu may have a modest effect, but there are no large-scale, high-quality human trials regarding its use via injection. The potential benefits of the cream do not prove that injecting the same substance would be effective or safe.
Injections may cause infection, allergic or immune reactions, and—if the dosage is incorrect—copper metabolism disorders. The long-term effects on the body are not yet sufficiently understood.
BPC-157 and TB-500
These are laboratory-synthesized peptides. BPC-157 and TB-500 are particularly popular among gym-goers because they are marketed as agents that accelerate the healing of muscles, tendons, and ligaments.
The problem is that most of the positive results come from cell and animal studies. There are very few, if any, high-quality human studies. These peptides also influence processes related to tissue repair and the formation of new blood vessels. This means that, in theory, such signals could also promote the growth of unwanted cells or tumors, but the extent of this risk in humans is not yet known (Vasireddi et al., 2025).
Why is the use of experimental peptides so dangerous?
The trend of injecting peptides, which is spreading among young people, is dangerous for several reasons. The problem is not only that the long-term effects of these substances have not yet been sufficiently studied in humans.
Many peptides sold online are not approved medications—that is, they do not have marketing authorization. This means that the drug regulatory agency has not confirmed that they are sufficiently effective, safe, and of high quality for a specific disease or purpose.
An approved drug must undergo several stages of testing before it can be sold. Researchers examine how the substance behaves in the body, what dosage is effective, what side effects occur, and for which people the drug is not suitable. The manufacturing facility, production conditions, and the purity, sterility, and shelf life of each batch are also strictly monitored.
In the case of a peptide sold online as a “research chemical”—a chemical intended for scientific research—such a system may not exist. A purity certificate provided on a website may not be independent, may not pertain to a specific batch, or may not prove that the vial sent to the buyer contains the same substance.
Furthermore, the synthesis of peptides is a complex process because amino acids must be linked in a very precise sequence. Byproducts with a nearly correct structure may form during production. Since such impurities resemble the actual peptide, they are harder to detect, and an unregulated manufacturer may not analyze them thoroughly at all.
Furthermore, it is unknown how different peptides interact with each other or with other medications. Social media often recommends using multiple substances at the same time. For example, a weight-loss peptide, a growth hormone-releasing peptide, and a recovery peptide might be combined. Such a combination may not have been studied in any human trials.
Even the intended effect of a substance can itself become dangerous. Retatrutide can suppress appetite so strongly that a person loses weight and muscle mass too quickly. MT2 stimulates other melanocortin receptors in addition to those in the skin. BPC-157 and TB-500 may influence signals related to blood vessel formation and tissue repair, but it is unknown how they affect existing abnormal cells.
The problem is particularly serious for young people, as their bodies and endocrine systems may still be developing. A severe reduction in appetite can affect muscles, bones, menstruation, sex hormones, mood, and athletic development.
Important to remember!
An unregulated peptide cannot in any way be compared to a regular dietary supplement. It is a biologically active experimental substance that is injected directly into the body.
The user takes at least three risks at once:
The unknown long-term effects of the substance itself.
The unknown quality of the product.
The risks associated with injection and dosing.
Essentially, the person is turning themselves into a test subject without a controlled preparation, a research physician, health monitoring, or an emergency plan.
The European Medicines Agency also warns that medications purchased from unregistered online sources may be counterfeit, substandard, and cause serious health damage. A product is not safer just because a website states “99% pure,” “third-party tested,” or “for research use only.” These phrases do not equate to a marketing authorization or proven safety.
Nevertheless, peptides represent a very exciting and rapidly evolving field of medicine that could prove highly beneficial in the future. Today’s experimental peptides may turn out to be useful medications, but first, their safety must be proven, the appropriate dosage determined, and long-term side effects studied.
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