This article explores peptides and their rapidly growing popularity. Videos circulating on social media present injectable research chemicals as a quick solution for weight loss, muscle growth, injury recovery or skin rejuvenation. At least, that is what influencers and self-proclaimed health experts promise.
The purpose of this article is to explain what a peptide is, how peptides work in the body and why some of them are useful as medicines but potentially dangerous when unregulated. It is not intended to promote them or provide instructions for use, but to help people assess the claims circulating on social media more critically.
What is a peptide?
A peptide is a compound made up of two or more amino acids linked by peptide bonds. Peptides act like messengers in the body, activating, inhibiting or regulating different processes.
One of the most common examples is insulin, which signals cells to take up glucose from the blood and promotes energy storage. This is why a person with type 1 diabetes who does not produce insulin needs to receive it by injection.
Another example is GLP-1, a hormone produced naturally in the gut and released after eating. GLP-1 tells the pancreas to release insulin when blood sugar rises, slows gastric emptying and sends a satiety signal to the brain. When discussing medicines, people usually mean GLP-1 receptor agonists, which mimic the effects of this hormone but remain in the body for much longer. In this way, they help regulate blood sugar, reduce appetite and keep people feeling full for longer (Müller et al., 2019).
How did peptides come to be used as medicines?
The use of peptides as medicines began with research into the body’s own hormones and signalling molecules. Scientists discovered that peptides give cells various instructions, such as regulating blood sugar, appetite, skin pigmentation and tissue repair. Because natural peptides break down quickly in the body, researchers began modifying them 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 initially be used as a medicine. In 1992, however, a similar, longer-acting peptide was found in the saliva of the Gila monster, a venomous lizard (Eng et al., 1992). This discovery was used to develop one of the first GLP-1 medicines.
Ozempic itself is not, of course, made from venomous lizard saliva, but this discovery contributed to its development.
Ozempic as a weight-loss medicine
The medicine was originally intended to help control blood sugar, but studies found that people using it also lost a noticeable amount of weight. By acting on the GLP-1 system, semaglutide reduces hunger, makes people feel full sooner and helps them eat less (Wilding et al., 2021).
Ozempic became especially well known in 2022, when celebrities and influencers began talking about the rapid weight loss they had achieved with it. Among the general public, the name Ozempic became almost a generic term for all GLP-1 weight-loss medicines. High demand even caused temporary shortages, affecting people who genuinely needed the medicine to manage diabetes.
Side effects of Ozempic
Ozempic can cause fairly rapid weight loss. During this process, people lose not only fat but also some muscle and bone mass (Wilding et al., 2021). The risk of muscle loss is higher if a person eats too little and does not do strength training.
A study published in 2024 involved 64 adults with an elevated risk of fractures. Over one 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 as a result of weight loss because a lighter body places less load on the bones (Hansen et al., 2024). The sample was also very small. There is currently no evidence that Ozempic causes osteoporosis or fractures in all users.
The greater danger is weight loss itself if a person does not consume enough protein to preserve muscle. Eating only small amounts of food may also lead to vitamin deficiencies.
How did peptides reach young people and fitness enthusiasts?
Peptides gained visibility among young people following Ozempic’s surge in popularity. Influencers began talking more and more about GLP-1 medicines, rapid weight loss and various injectable peptides.
Social media often creates the impression that peptides are a safer alternative to steroids. In reality, many of them are potent signalling molecules that affect appetite, blood sugar, growth hormone, pigmentation and tissue growth.
Retatrutide, MT2, GHK-Cu and other peptides are among those most frequently discussed by young people and fitness enthusiasts.
Retatrutide, or “Reta”
Retatrutide is an experimental weight-loss peptide similar to Ozempic but with stronger and broader effects. While semaglutide acts on one hormone receptor, retatrutide acts on three at once: the GLP-1, GIP and glucagon receptors (Jastreboff et al., 2023).
In a 2023 study, people 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 spread across social media even before receiving official approval.
As of August 2026, retatrutide is not an approved medicine. It is still being studied, and substances sold online do not come from any official pharmaceutical packaging.
Potential side effects identified for retatrutide include nausea, vomiting, diarrhoea, constipation, a very substantial reduction in appetite and an increased heart rate. Losing weight too quickly may also increase the risk of gallstones, malnutrition and hormonal disorders. Not all of its effects are yet fully understood (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 creates a tan quickly without the need to spend a long time in the sun (Dorr et al., 1996).
However, it is not a safe injection. MT2 affects several receptors, which means it may cause nausea, facial flushing, headaches and reduced appetite (Dorr et al., 1996).
Cases of melanoma have also been reported after MT2 use, but it is currently impossible to say with certainty whether they were caused by MT2, intense UV exposure or a combination of the two (Hjuler & Lorentzen, 2014).
GHK-Cu, or copper peptide
GHK-Cu is a short peptide found in the human body that binds and transports copper. Copper is needed, for example, by enzymes involved in collagen formation. When tissue is damaged, GHK-Cu may act as a kind of repair signal. It is important to remember that it has very broad effects: it carries copper and influences the activity of several cells, enzymes and genes (Pickart et al., 2015).
GHK-Cu is promoted as a way to rejuvenate the skin, boost collagen production, improve wound healing and stimulate hair growth.
GHK-Cu may have a modest effect in topical cosmetic products, but there are no large, high-quality human trials on injecting it. The potential benefits of a cream do not prove that injecting the same substance is effective or safe.
Injection may cause infection, an allergic or immune reaction and, if the amount is incorrect, a disruption of copper metabolism. Its long-term effects on the body are not yet sufficiently understood.
BPC-157 and TB-500
These are laboratory-made peptides. BPC-157 and TB-500 are especially popular among gym-goers because they are promoted as a way to speed up the healing of muscles, tendons and ligaments.
The problem is that most positive results come from cell and animal studies. There are very few high-quality human trials, if any. These peptides also affect processes involved in tissue repair and the formation of new blood vessels. This means that, in theory, such signals could also influence the growth of unwanted cells or tumours, but the magnitude of this risk in humans is not yet known (Vasireddi et al., 2025).
Why is using experimental peptides so dangerous?
The trend of injecting peptides among young people is dangerous for several reasons. The problem is not limited to the fact that the long-term effects of these substances have not yet been sufficiently studied in humans.
Many peptides sold online are not approved or authorised medicines. This means that a medicines regulator has not confirmed that they are sufficiently effective, safe and high-quality for a specific condition or purpose.
Before an approved medicine can be sold, it must pass through several stages of research. Researchers examine how the substance moves through the body, which dose works, what side effects occur and which people should not use the medicine. The factory, manufacturing conditions and the purity, sterility and shelf life of every batch are also strictly controlled.
Such a system may not exist for a peptide sold online as a “research chemical”, meaning a chemical intended for research. A certificate of purity shown on a website may not be independent, may not apply to the specific batch and does not prove that the vial sent to the buyer contains the same substance.
Manufacturing peptides is also a complex process because the amino acids must be joined in a very precise sequence. Production may create by-products with an almost correct structure. Because these impurities resemble the actual peptide, they are more difficult to detect, and an unregulated manufacturer may not analyse them thoroughly at all.
It is also unknown how different peptides interact with one another or with other medicines. Social media often recommends using several substances at the same time. For example, a weight-loss peptide may be combined with a growth hormone-releasing peptide and a recovery peptide. Such a combination may never have been studied in a human trial.
Even a substance’s intended effect may itself become dangerous. Retatrutide may suppress appetite so strongly that a person loses weight and muscle mass too quickly. In addition to its effects on the skin, MT2 also stimulates other melanocortin receptors. BPC-157 and TB-500 may affect signals involved in blood vessel formation and tissue repair, but their effects on existing abnormal cells are unknown.
The problem is particularly serious for young people because their bodies and hormonal systems may still be developing. Strong appetite suppression may affect muscles, bones, menstruation, sex hormones, mood and athletic development.
Important to remember!
An unregulated peptide cannot be compared to an ordinary 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 of injection and dosing.
In essence, the person turns themselves into a test subject without a controlled product, a study physician, medical monitoring or an emergency plan.
The European Medicines Agency also warns that medicines purchased from unregistered online sources may be counterfeit, poor-quality and capable of causing serious harm to health. A product is not safer simply because its website says “99% pure”, “third-party tested” or “for research use only”. These phrases do not amount to marketing authorisation or proven safety.
Nevertheless, peptides are a fascinating and rapidly developing field of medicine with the potential to provide significant benefits in the future. Today’s experimental peptides may turn out to be useful medicines, but their safety must first be demonstrated, an appropriate dose established and their long-term side effects studied.
How much do you remember? Answer the review questions below correctly to earn a FitQ knowledge point. You’ll earn one point for every article whose questions you answer correctly.
