What are peptides? An honest sorting between medicine and grey zone
The same word stands for three completely different worlds. For one of the best researched drug fields of our time, for cosmetics with thin data, and for vials from the internet whose content nobody knows.
Peptides are neither a trend nor a scandal. They are a size label. And because the same size label sits on an insulin ampoule, on a night cream and on a grey vial from the internet, you need a map before you judge any of it.
You have read the word everywhere over the past months. On a jar in the drugstore. In a podcast about longevity. In a forum where somebody reports that after a tendon injury he injected something that comes from Croatia and is sold online as a research chemical.
And somewhere in between, in a completely different league, run the medicines that are currently reshaping obesity care.
All of that is called peptide. And that is exactly the problem.
I am writing this text because I see both ends of this spectrum in my practice. People who receive a well supported, prescription only peptide therapy and are unsettled anyway. And people who inject something whose purity nobody has ever checked. Both groups use the same word.
What you will find here
- What a peptide actually is biochemically, in one image
- Why the word says nothing about benefit or safety
- World 1: approved peptide medicines and their evidence
- World 2: peptides in creams and what the trials give us
- World 3: research peptides from the internet, seen soberly
- What a laboratory analysis actually found in online vials
- Why signalling molecules can trigger feedback
- Three levers you can put in place today
A peptide is a short sentence, not a whole book
Let us start where it is easy.
Amino acids are the letters of life. Twenty of them, and your body builds everything made of protein from those. Link two or three of them together and you get a very short word. Link ten or thirty together and you get a sentence. That is a peptide.
Link hundreds together, and let the chain fold into a complicated three dimensional shape, and you get a protein. A whole book.
The boundary between the two is a convention, not a law of nature. Usually anything up to roughly fifty amino acids is called a peptide, and anything above that a protein. Insulin sits at exactly that threshold with fifty one amino acids and is still mostly listed as a peptide hormone.
The word “peptide” describes a length. It describes no benefit, no safety and no approval. That is precisely where the risk of confusion lies, on the shelf as much as online.
So why does the length still matter so much? Because it decides what happens to the molecule once it enters your body.
Your digestive system is a machine for taking protein apart. Stomach acid unfolds the chains, enzymes from the stomach, the pancreas and the lining of the small intestine cut them into ever shorter pieces. What is left at the end are single amino acids and very short remnants that can be absorbed.
A Chinese research group collected what happens to food derived oligopeptides during simulated passage through the stomach and gut. They describe how the chains become systematically shorter while hydrophobic and basic amino acids are exposed at the ends.
Decisive for the sorting is their second finding: the biological activity of the peptides decreased after simulated uptake in the intestine. What comes through the gut wall most nearly unchanged are very short chains, essentially di-, tri- and tetrapeptides.
What this means for you: when a tin says it contains a certain peptide, the first question is not how much is in there, but how much of it arrives intact at all.
Liu W et al. Int J Food Sci Nutr. 2024. DOI: 10.1080/09637486.2023.2295224Most peptide medicines are not injected because that looks more impressive. They are injected because your gut would otherwise take them apart before they arrive anywhere.
That, by the way, is a good first filter for every peptide promise: how is the molecule supposed to get to the place where it is meant to do something?
And now you know why the word peptide means the same thing on a package insert and on a cream jar and still refers to something completely different.
Three worlds that all go by the name peptide
Before we go into detail, you need the sorting. Without it, every discussion about peptides turns into an argument where both sides are talking about something different.
I separate three worlds. They have different legal situations, different data and different risks.
Approved and tested
Insulin, GLP-1 receptor agonists, teriparatide, desmopressin, octreotide, GnRH analogues. Approval trials with thousands of people, a defined indication, known side effects.
The condition: prescription only, a medical indication, monitoring. Not freely available, and for good reason.
Peptides in creams
Matrixyl, Argireline, GHK-Cu. Applied to the skin, not injected. Legally cosmetics, not medicines.
The data: many small trials, often short, often funded close to the manufacturer. Effects moderate. Compared with an injection the risk is low, but it is not zero. Contact allergies, redness and irritation do occur.
So called research peptides
BPC-157, TB-500, CJC-1295, Ipamorelin, MOTS-c and others. Sold online as research chemicals, explicitly not for human use.
No marketing authorisation, data mostly from animals and cell culture, no guarantee of purity or sterility when bought through grey channels.
Peptides as food
Collagen peptides and other protein hydrolysates are swallowed and are legally treated as supplements.
A completely different category and a completely different safety question. There is a separate article on that in this guide.
When somebody tells you “peptides are great” or “peptides are dangerous”, both sentences are missing the same piece of information: which ones.
Insulin and an unchecked vial from an online shop have something in common chemically and almost nothing in common medically.
And now you know why I insist so stubbornly on categories in this topic.
World 1: the peptides that really are medicine
Let us start with the part that often gets lost because it sounds less exciting.
Peptides are among the most successful drug classes in modern medicine. Since insulin was introduced a good hundred years ago, more than eighty peptide drugs have made it to market approval worldwide, for diabetes, cancer, osteoporosis, multiple sclerosis, HIV and chronic pain.
One word of demarcation before I go on: these applications sit in oncology, neurology and infectious disease medicine. They are indicated and supervised there, in specialised centres. They are not the subject of this text and not the subject of my practice. I name them only to show how broad this field of active substances is. The same goes for the neuroendocrine tumours and for oncology further down.
A review in Nature Reviews Drug Discovery summarised the development of peptide drugs since insulin. Four researchers from Australia and Austria describe the developmental lines: from human hormones through targeted chemical optimisation to peptides derived from animal venoms or from libraries.
Their conclusion is sober and important for the sorting: peptides are pharmacologically fascinating because they can bind very specifically to their target structures. They are also hard to handle, because they are degraded quickly and pass poorly through membranes.
What this means for you: every approved peptide medicine is the result of a long chemical struggle for stability and dosability. A raw peptide from the internet has not been through that development.
Muttenthaler M et al. Nat Rev Drug Discov. 2021. DOI: 10.1038/s41573-020-00135-8Insulin and the GLP-1 receptor agonists
Insulin is the peptide hormone your pancreas releases when sugar arrives in the blood. As a medicine it has been in use since the 1920s. Before it was discovered, type 1 diabetes was a fatal disease. Today it is treatable.
The second large group are the GLP-1 receptor agonists. GLP-1 is a gut hormone, also a peptide. It is released when food arrives in the small intestine. It can increase insulin release, dampen glucagon, slow gastric emptying and influence the feeling of fullness in the brain.
The trick of the medicines: your own GLP-1 is broken down within minutes. Semaglutide and liraglutide are altered so that they stay stable much longer.
In a double blind randomised trial with 1,961 adults with obesity and without diabetes, 2.4 mg semaglutide or placebo was given weekly over 68 weeks, in both cases on top of a lifestyle intervention. Mean body weight fell by 14.9 percent in the semaglutide group and by 2.4 percent under placebo.
A second, considerably larger trial with 17,604 people with pre-existing cardiovascular disease and overweight, but without diabetes, looked at hard endpoints over almost four years. The combined endpoint of cardiovascular death, heart attack and stroke occurred in 6.5 percent under semaglutide and in 8.0 percent under placebo.
Important for honesty: in that trial 16.6 percent of the semaglutide group stopped treatment because of side effects, compared with 8.2 percent under placebo. Benefit and side effects belong in the same sentence, always.
Important for context: these figures come from approval trials that the manufacturer funded. They apply to the approved indication, that is to obesity or to overweight with a weight related condition, and only after a medical indication has been established. For use on purely cosmetic grounds there is neither an approval nor a data basis. I write this here as orientation on a field of research, not as an offer.
Wilding JPH et al. N Engl J Med. 2021. DOI: 10.1056/NEJMoa2032183 · Lincoff AM et al. N Engl J Med. 2023. DOI: 10.1056/NEJMoa2307563Teriparatide, desmopressin, octreotide, GnRH analogues
Less well known, but just as instructive, are the other peptide medicines. They show how different the tasks can be.
Teriparatide is a fragment of the parathyroid hormone, the first 34 amino acids. In severe osteoporosis it is injected under the skin daily. In the approval trial with 1,637 women after the menopause, new vertebral fractures occurred in 14 percent under placebo and in 5 percent under 20 micrograms of teriparatide.
What is interesting about this example is the dose question. Permanently elevated parathyroid hormone can break bone down. In short daily pulses, the same hormone fragment can stimulate bone building. Same substance, different timing pattern, opposite effect.
The Fracture Prevention Trial randomised 1,637 women after the menopause who had already suffered vertebral fractures to 20 or 40 micrograms of parathyroid hormone fragment or placebo, daily subcutaneously, over a median of 21 months.
New vertebral fractures occurred in 14 percent under placebo and in 5 and 4 percent respectively in the treatment groups. Non-vertebral fractures were rarer too. The higher dose raised bone density more, but brought no additional fracture protection and more side effects.
A follow-up over a further 18 months after stopping found a lasting advantage of 41 and 45 percent respectively compared with placebo. That belongs to the sorting as well: a time limited therapy can have an after effect.
That follow-up, however, ran open, no longer blinded, and close to half of the women took other osteoporosis medicines during that time. The advantage remained measurable nonetheless. What is firmly supported is less than the figure promises at first glance.
Neer RM et al. N Engl J Med. 2001. DOI: 10.1056/NEJM200105103441904 · Lindsay R et al. Arch Intern Med. 2004. DOI: 10.1001/archinte.164.18.2024Desmopressin is a chemically altered version of your own antidiuretic hormone. In diabetes insipidus it can slow water loss through the kidney, and it is also used in certain bleeding tendencies. That is precisely why it is not a harmless remedy: anyone who drinks too much while taking it can develop a dangerous dilution of the sodium in the blood.
Octreotide and related somatostatin analogues can dampen the release of growth hormone and are used in acromegaly and in certain neuroendocrine tumours. GnRH analogues intervene in the higher level control of the sex hormones and are used in endocrinology, reproductive medicine and oncology.
All of these peptides act at a defined receptor site inside a control system. They are prescription only because exactly that is an intervention and not a supplement.
And all of them were tested in trials with hundreds to tens of thousands of people before they were approved. That number is the real difference to world 3.
And now you know why I deal with this group first. It is the yardstick everything else should be measured against.
World 2: peptides in creams, between chemistry and marketing
You are standing in front of the shelf with the facial care products. One jar says Matrixyl, the next one Argireline, the third one copper tripeptide. And you wonder whether this is chemistry or poetry.
The honest answer is: a bit of both.
The idea behind cosmetic peptides is plausible. When collagen in the skin is broken down, short fragments are produced. Some of these fragments appear to signal to the skin that repair is needed. If you apply similar short chains from outside, you might imitate that signal.
Argireline follows a different approach. The hexapeptide is meant to dampen the release of messengers at the junction between nerve and muscle and thereby reduce the tension of the facial muscles, in a very weakened form similar to a well known nerve toxin from aesthetic medicine.
The comparison limps on purpose. There are no direct comparative trials between such a cream and the procedure from aesthetic medicine, and the order of magnitude of the effects is a completely different one.
The copper tripeptide GHK-Cu in turn occurs naturally in human blood plasma and has been studied for decades in the context of wound healing.
A systematic review compared different topical cosmeceuticals in light induced skin ageing: plant based actives, peptides and hydroquinone.
The authors rated the evidence base for peptides as the strongest within the groups examined, with several trials at a high level of evidence. The following qualification does not come from the review, it is my own assessment: for this field in general the trials are small, run for a short time and are often funded by the manufacturers of the tested products.
What this means for you: a peptide cream can influence the appearance of the skin favourably. It remains a surface measure next to the factors with the greatest leverage: sun protection, sleep, not smoking and nutrition.
Chan LKW et al. Skin Res Technol. 2024. DOI: 10.1111/srt.13730A Polish research group packed the copper tripeptide GHK-Cu into liposomes, tiny fat envelopes meant to improve uptake into the skin, and tested the effect on two enzymes.
On tyrosinase, the enzyme of pigment formation, GHK-Cu had no noteworthy influence in this experiment. On elastase, the enzyme that breaks down elastin, an inhibition of about 49 percent appeared.
For context: this is a test tube experiment, not a trial in humans. It makes it plausible why GHK-Cu is being studied. It says nothing about what is visible on your face after three months.
Dymek M et al. Pharmaceutics. 2023. DOI: 10.3390/pharmaceutics15102485A word on the risks, because “only a cream” does not mean “without risk”. Contact allergies, redness and irritation do occur with cosmetic peptides, GHK-Cu and Argireline included. The eye area and skin that is already damaged are particularly sensitive. If a reaction does not settle, stop the product and have it assessed by a dermatologist.
The decisive difference between world 2 and world 3 is not the class of substance. It is the route into the body.
A cream stays largely outside. An injection bypasses every barrier your body has placed between itself and the environment. That is why the safety question in world 3 is a completely different one.
And now you know why I consider cosmetic peptides a legitimate but small topic.
World 3: the so called research peptides, seen soberly
Now comes the part you probably searched for this article for.
Names like BPC-157, TB-500, CJC-1295, Ipamorelin, MOTS-c and retatrutide circulate online. The promises attached to them read like a wish list: faster healing after injuries, more muscle, less fat, more energy, slower ageing.
I do not want to frighten you here and I do not want to sell you anything. I want to show you how I sort these substances and why.
What sits behind the names
BPC-157 is a pentadecapeptide, a chain of fifteen amino acids derived from a protein fragment of human gastric juice. It has been studied in animal models for more than three decades, above all by a research group in Zagreb.
TB-500 is a fragment of thymosin beta-4, a peptide of the body that plays a role in embryonic development and in tissue repair. CJC-1295 and Ipamorelin belong to the substances meant to stimulate the release of growth hormone. MOTS-c is a peptide encoded in the mitochondrial genome and has been linked in animal experiments to metabolism and adaptation to exertion. Retatrutide is a triple agonist at GIP, GLP-1 and glucagon receptors and is in clinical development.
What the data actually looks like
And this is where the advertising parts ways with the science.
In a rat study, the tendon of the four headed thigh muscle was detached from the muscle, a defect that does not heal on its own in these animals. Over six weeks, the treated animals showed clearly better courses in the measures of mobility, tissue appearance and function than the untreated ones.
A second piece of work on isolated tendon cells from the Achilles tendon of rats found that BPC-157 increased the equipment of these cells with growth hormone receptors in a dose and time dependent way, which increased cell division under growth hormone.
Important for the sorting: these are animal and cell experiments. They explain why the substance attracts interest. They say nothing about what happens in a human being with an irritated tendon.
Japjec M et al. Biomedicines. 2021. DOI: 10.3390/biomedicines9111547 · Chang CH et al. Molecules. 2014. DOI: 10.3390/molecules191119066The decisive question is not whether something happens in an animal model. The decisive question is what is supported in humans. And there it gets very thin.
A biopharmaceutical review systematically worked through the development status of BPC-157, including patent databases and the websites of the FDA, the EMA and the World Anti-Doping Agency.
Their finding: despite more than thirty years of preclinical research there is no approved dosage form, no validated dosing scheme and no completed phase II trial. The available clinical data comes from fewer than thirty people in three uncontrolled pilot attempts, none of them with a standardised pharmaceutical preparation.
The authors put it plainly: the main obstacle is not a lack of biological activity, but a lack of basic pharmaceutical science, meaning characterised formulations and validated pharmacokinetics.
One finding from the same paper matters especially for any self application: the plasma half-life is under half an hour, while the described effects are said to last for hours to days. This contradiction is unresolved. As long as it is unresolved, no sensible dosing can be derived from the available data at all.
Mateescu DM et al. Pharmaceutics. 2026. DOI: 10.3390/pharmaceutics18050625 · Józwiak M et al. Pharmaceuticals. 2025. DOI: 10.3390/ph18020185With TB-500 and MOTS-c the situation is comparable. For thymosin beta-4, reviews describe effects on cell migration and cell survival in the mouse heart model, explicitly as basic research with a view to future regenerative therapies. For MOTS-c, reviews summarise effects on glucose and fat metabolism as well as on inflammatory processes and discuss it as a possible mimic of exercise stimuli. Both are hypotheses at the research stage, not recommendations for use.
Retatrutide is the interesting special case in this list, because there really is human data from a controlled trial.
First things first, because it otherwise gets lost: retatrutide holds no marketing authorisation in any country to this day. It is in clinical testing. The trial below was funded by the manufacturer.
In a double blind, placebo controlled phase 2 trial with 338 adults with obesity, or with overweight plus a weight related condition, retatrutide was injected under the skin once a week over 48 weeks. Mean body weight fell by 24.2 percent under the highest dose, compared with 2.1 percent under placebo.
Honesty means naming the other side too. The most common side effects were gastrointestinal and dose dependent. Heart rate also rose in a dose dependent way, peaking at 24 weeks.
I name this figure so that you can place it, not so that you go looking for it. A phase 2 trial says nothing about rare side effects and nothing about safety over years. That is exactly what phase 3 is for, and it is still running.
What this means for you: that is impressive. It is also exactly what a phase 2 trial is: an intermediate step, not proof for approval.
Jastreboff AM et al. N Engl J Med. 2023. DOI: 10.1056/NEJMoa2301972Anyone who gets hold of this substance online today is not taking part in a trial and has no safety net at all.
Preclinically exciting is not the same as supported in humans. Between the two lies the whole rest of drug development.
A risk that is often overlooked: what is in the vial
And now comes the point that occupies me most in my practice. It has nothing to do with the substance itself.
A research group from Hungary and the USA investigated in 2024 what happens when you buy semaglutide without a prescription from illegal online pharmacies. They evaluated 1,080 search engine links, identified 59 illegal sellers and made test purchases.
Three out of six orders arrived at all, the others were simply fraud. In the vials that were delivered, the measured active ingredient content was 28.6 to 38.7 percent above the label. The measured purity was between 7.7 and 14.4 percent, while 99 percent was stated. Bacterial endotoxins were detected in all samples.
Completeness means naming the other side of that finding too: no viable microorganisms were found in the freeze dried samples at the time of testing. So the problem was not the living germ, but its residues and the completely unknown content.
What this means for you: even if a substance were unproblematic in itself, buying through grey channels leaves you knowing neither how much you are injecting nor what else goes in with it.
Ashraf AR et al. J Med Internet Res. 2024. DOI: 10.2196/65440On top of that comes a second point that is often overlooked: doping relevance. Anyone active in organised sport should know that several of these substances are in the focus of doping analytics. A detection method from the Institute of Biochemistry at the German Sport University Cologne explicitly lists CJC-1295, alongside insulins, growth factors and GnRH, among the peptides banned in competitive sport. Ghrelin, the body's own hunger hormone, is on the banned list too because of its growth hormone releasing properties.
For the research peptides named here something is added that is often overlooked. The prohibited list of the World Anti-Doping Agency treats substances without regulatory approval for human use as banned in principle, even when they are not listed individually by name. Anyone competing under a federation should check this in the current version of the list before every substance. It is not only about health, it is also about a ban.
For none of the so called research peptides is there a marketing authorisation in Europe for use in humans. That means: no tested purity, no tested sterility, no validated dosing, no systematic recording of side effects and no data on long term risks.
Injections of non-sterile preparations can trigger abscesses and severe infections. Endotoxins can cause fever and circulatory reactions. Substances that intervene in the growth hormone axis can change blood sugar metabolism. With an existing tumour disease, in pregnancy and breastfeeding, in kidney or liver disease and while on long term medication, any self application is particularly risky.
One point is regularly overlooked with semaglutide obtained through grey channels: anyone taking insulin or sulfonylureas at the same time can become severely hypoglycaemic on it. Without a prescription, without training and without monitoring, exactly the framework that can catch this danger is missing.
This applies to children and adolescents in particular. Substances that intervene in the growth hormone axis can have consequences that cannot be reversed while growth is still ongoing. And this is exactly the group most often addressed in the fitness scene.
And if you have already injected something: watch the injection site. Redness, warmth, swelling or pain that increase instead of subsiding should be looked at by a doctor the same day. Fever, chills or a circulatory collapse after an injection are an emergency, then please call the emergency number, 112 in Germany. Say openly what you gave yourself. That is not a question of embarrassment, it is the information that makes treatment right in the first place.
For that reason you will find no sources of supply, no doses and no instructions for use in this text. That is not censorship, that is a stance: curiosity yes, self experiment with unregulated goods no.
And now you know why I am more outspoken on this topic than usual.
Peptides are signalling molecules, and signals have feedback
There is one thought that matters to me even more with peptides than with vitamins and minerals. It is the red thread through this whole guide.
Your body does not regulate in switches, it regulates in loops. Almost every signal that arrives somewhere creates a counter movement somewhere else. That is not a weakness of the system, it is its intelligence. It is called homeostasis.
Peptides are almost always exactly that: signalling molecules. They tell a cell to do something or to stop doing it. When you add such a signal from outside, you are not acting at a single point. You are acting inside a control loop.
Nervous system
Fullness and hunger are not questions of willpower, they are peptide signals. GLP-1 from the gut reaches nuclei in the brainstem and hypothalamus and can dampen food intake. Anyone who strengthens that signal pharmacologically changes not only a weight, but a perception.
Metabolism
Insulin and glucagon are two peptides that work against each other and thereby keep blood sugar in a narrow window. Turn one side of this pair and you automatically move the other. That is why insulin therapy without training can be dangerous.
Hormone system
Growth hormone is released not continuously but in pulses, steered by two opposing peptides from the hypothalamus. Substances meant to push this axis from outside intervene in a finely timed feedback system whose long term consequences in humans are barely studied.
Immune system
Immune defence works with peptides too, for example antimicrobial peptides on mucous membranes and messengers between immune cells. Protein foreign to the body can in principle trigger an immune response, up to antibodies against the peptide that was added. With unchecked preparations this risk cannot be estimated.
You know the same logic from the rest of this guide. Zinc at high doses over months can push down copper uptake. Vitamin D at high doses without magnesium and vitamin K2 can shift the calcium balance. This has been discussed for years, robust human studies on it are still thin. Single B vitamins at high doses can shift the pattern of the others. Iron in the presence of silent inflammation can be counterproductive.
A nutrient is not a switch, it is a player in a network. For peptides that holds even more strongly, because they are not building material but instruction.
This is not about a molecule. It is about the question of whether you trust your body to be able to do something you do not fully understand yet.
I am not an opponent of intervention. I am a physician, I intervene every day. But I want to know which loop I am reaching into before I do it. This attitude is not a brake. It is the difference between treatment and gambling.
And now you know why the word homeostasis shows up in almost every article of this guide.
Same substance, two worlds: why the dose changes everything
There is a thinking error that shows up with peptides just as it does with vitamins. It goes: if a small amount is good, a large amount must be better.
In medicine that is almost never true. And there is a distinction I consider so important that I repeat it in every article of this guide.
| Covering requirements | Orthomolecular high dose therapy | |
|---|---|---|
| Goal | fill gaps, secure supply | influence a process on purpose, like a medicine |
| Dose range | around the official reference values | a multiple of that |
| Supervision | mostly none, self purchase common | medical, with baseline labs and interim checks |
| Duration | often permanently low | time limited, with an exit plan |
| Expected effect | no therapeutic effect to be expected | can be therapeutically relevant, with the matching risks |
The classic example for this is vitamin D. To cover requirements, the orders of magnitude named by the professional societies sit in the low four figure range of International Units per day, and the exact number differs from society to society and with the starting value. In multiple sclerosis, by contrast, there is an experimental approach that works with a multiple of that amount, under close medical supervision.
I deliberately name no figures here, and I mention this example explicitly not as a recommendation. It is an experimental therapeutic approach, not an established standard, and it is not recommended in any guideline. Without medical supervision it is dangerous, because hypercalcaemia can develop. I do not offer this procedure. But it shows the principle crystal clearly: the same substance, two completely different applications.
A group at Tübingen University Hospital reported on two people, a 53 year old woman and a 33 year old man, who came to the clinic with a life threatening hypercalcaemic crisis. Both had taken high dose vitamin D preparations on their own over months, cumulatively in the range of 2.5 to 10 million International Units.
The measured 25-OH vitamin D levels were 663 and 1,289 nmol per litre, while the reference range of the clinic was 50 to 175. Forced diuresis and bisphosphonates were not enough, plasma exchange and special dialysis procedures were used. It took 355 and 109 days respectively until the values were largely back in the target range.
What this means for you: high dose is not a diligence exercise. It is a medical procedure with a risk profile of its own and it belongs under medical supervision.
Heister DJ et al. J Nephrol. 2022. DOI: 10.1007/s40620-022-01543-2With peptides the same logic applies, only with an extra catch. With a vitamin you at least know the dose. With a vial from an online shop whose measured purity can lie between eight and fourteen percent, you do not even know that.
The difference between a supplement and a therapy is not the substance. It is the dose, the indication, the monitoring and the time frame.
Anyone expecting a therapeutic effect from a requirement covering dose will be disappointed. Anyone taking a therapeutic dose without medical supervision is taking a risk they cannot survey.
And now you know why with every peptide question I first ask: which dose, which goal, who is watching along?
Real food first, and why topping up is still more often justified today
Maybe you are thinking now: if you are that careful, are you in favour of supplements at all?
Yes. But in a certain order.
Nutrient supply from natural, real food of good origin and good husbandry is always the first choice. A food delivers its nutrients in a matrix of cofactors, fibre and secondary plant compounds that no capsule rebuilds. And with protein there is something that fits this topic especially well: from a piece of fish or a handful of lentils, short peptides are constantly produced during digestion anyway, and your body processes them further itself.
No supplement replaces nutrition, sleep, movement, sun and relationship. That is not a moral statement. Going by everything I see and read, I consider this order the more sensible one.
Even so, targeted topping up is more often justified today than fifty years ago. Not because supplements are fashionable, but because the conditions have changed.
Four reasons, honestly named with their limits
- Soils, varieties, storage. For some nutrients, comparative data across decades shows lower contents in fruit and vegetables. Important for honesty: the comparability of old and new analytical methods is methodologically contested, and part of the effect is explained by higher yielding varieties, that is by dilution.
- Highly processed foods. They deliver a lot of energy at low micronutrient density. In Western countries a high share of daily energy intake comes from this group.
- Environmental exposure and constant stress. Heavy metals, mould toxins, plasticisers and pesticide residues as well as chronic stress can increase the consumption of protective substances such as zinc, selenium, magnesium and glutathione precursors.
- Medicines as nutrient robbers. Some combinations are well studied, others much less so. Among those discussed are proton pump inhibitors and B12 or magnesium, metformin and B12, diuretics and potassium or magnesium, and the pill and B6, B12, folate and zinc. For statins and coenzyme Q10 the data are contradictory. Whether a real need follows from this can only be clarified case by case and with a doctor. Very important, so that no misunderstanding arises here: not one of these points is a reason to stop or reduce a prescribed medicine. The benefit of these medicines is as a rule considerably greater than the nutrient question. Raise it, change nothing on your own.
And of all things, the most modern peptide therapy delivers a new example of this. Anyone eating considerably less under a GLP-1 receptor agonist is not only eating fewer calories.
A review in Nutrients collected what nutritional support people on GLP-1 receptor agonists need, using the established aftercare pathways following bariatric surgery as a frame of comparison.
The authors name four construction sites: reduced food intake overall, gastrointestinal complaints, loss of fat free mass and micronutrient deficits. Their conclusion: drug based weight therapy should not run as pure prescription writing, but with structured nutritional support, especially with an eye on protein intake.
What this means for you: even with a well supported peptide medicine, the capsule or the injection is only one part. The rest stays nutrition, strength training and monitoring.
Balasubaramaniam V et al. Nutrients. 2026. DOI: 10.3390/nu18162643My attitude to this is simple: I would rather know what I am doing. A baseline finding, a clear goal, a time limited intervention and a check-up appointment.
Supplements are as a rule a time limited intervention with a goal and a check, not a lifelong subscription. There are well founded exceptions, for instance B12 after stomach surgery, vitamin D in winter at our latitudes or targeted substitution in chronic malabsorption. And that is exactly what they are: well founded exceptions, not the rule.
And now you know why the same question stands before every capsule and every vial with me: what exactly is supposed to change, and how would we notice it?
Three levers you can put in place today
No protocol, no weekly plans, no brands. Just three things that lie in your hands.
Lever 1: sort before you judge
- Next time somebody tells you about peptides, ask a single question back: which world? Medicine, cosmetics or research chemical?
- That one question clears up the greater part of the confusion before the discussion even begins.
- One clue that almost always holds: when a product is explicitly sold as “not for human consumption”, that is not a legal formality. It is the most honest statement on the label.
Lever 2: check the route into the body
- Ask with every peptide promise: how is the molecule supposed to get to the place where it is meant to do something?
- Swallowed peptides are largely taken apart in the digestive tract, and that is well documented. Applied peptides mostly stay on the surface.
- Everything that is injected bypasses your barriers. That is exactly where the question of sterility and purity is not a side issue but the main issue.
Lever 3: bring the basics before the building block
- Before you think about regenerative peptides, look at the factors for which the data on tissue healing is best: protein intake, sleep duration, blood sugar stability, movement, stopping smoking.
- With persistent tendon or joint complaints, the orthopaedic assessment belongs at the beginning, not the laboratory. A tear, an enthesitis, an inflammatory rheumatic cause or tendon damage triggered by certain antibiotics do not necessarily show up in a blood count.
- If you have complaints that do not go away, a baseline finding makes more sense than an order. Ferritin, vitamin D, B12, thyroid and inflammation markers can explain a surprising amount. Sometimes they explain nothing. That is a result too, and then the search goes on, instead of a vial replacing it.
- If you are still thinking about a peptide therapy, raise it with a physician. For many concerns there are approved routes, and those come with a safety net.
All approved peptide medicines named in this text are prescription only. They have relevant interactions and contraindications. GLP-1 receptor agonists can trigger gastrointestinal complaints. Among other things they are not suitable with pancreatitis in the history, with medullary thyroid carcinoma or multiple endocrine neoplasia type 2 in personal or family history, with gastroparesis and with severe gastrointestinal disease. In pregnancy and breastfeeding they are not indicated, and before a planned pregnancy a time interval is foreseen. The European Medicines Agency has also reviewed reports of psychiatric side effects. What is binding is always the current summary of product characteristics, not this text. Desmopressin can lead to a dangerous drop in sodium if too much is drunk. Teriparatide is subject to a time limit on the duration of use. In pregnancy and breastfeeding, in kidney and liver disease, in tumour disease and while on blood thinning, separate rules of caution apply in each case.
For supplements it holds that the upper intake levels set by the authorities are not target values, they are upper limits. Anyone taking medication regularly should have any additional intake checked medically.
This text is information and orientation. It does not replace a medical examination, a diagnosis or individual advice.
And now you know why the most honest answer to “what are peptides” begins with a question in return.
Common questions about peptides
What are peptides, simply explained?
A peptide is a short chain of amino acids.
Amino acids are the letters, peptides are short sentences, proteins are whole books. The boundary is a convention: chains of up to roughly fifty amino acids are usually called peptides, longer chains are called proteins.
Your body makes hundreds of peptides itself and uses them as signalling molecules. Insulin is a peptide, many hormones in the gastrointestinal tract are peptides, and parts of your immune system work with peptides too.
So the word says something about size only, nothing about benefit, safety or approval.
Are peptides the same as proteins?
No, but they are relatives.
Both are made of amino acids linked by the same chemical bond. The difference is length, and with it the folding. Proteins fold into complex three dimensional shapes, peptides are shorter and more flexible.
In practice that makes a big difference: many peptides are broken down quickly in the gastrointestinal tract and therefore hardly reach the blood intact when you swallow them.
That is one of the reasons why most peptide medicines are injected.
Which peptides are approved as medicines in Germany?
Quite a few, and they are among the best studied medicines there are.
They include insulin and its analogues, the GLP-1 receptor agonists such as semaglutide and liraglutide, teriparatide in severe osteoporosis, desmopressin in diabetes insipidus and in certain bleeding tendencies, somatostatin analogues such as octreotide in acromegaly and neuroendocrine tumours, and GnRH analogues in endocrinology and oncology. The oncological and endocrinological applications sit in specialised fields and are not the subject of my practice.
A review in Nature Reviews Drug Discovery counted more than eighty approved peptide drugs worldwide. How many of them are available in Germany depends on the respective approval procedure. What is binding is always the current summary of product characteristics.
All of these are prescription only and belong in medical hands.
What are research peptides such as BPC-157 or TB-500?
These are substances sold on the internet as so called research chemicals, not as medicines.
BPC-157, TB-500, CJC-1295, Ipamorelin and similar names show up there. For none of them is there a marketing authorisation in Europe for use in humans.
The data comes overwhelmingly from animal experiments and cell cultures.
A biopharmaceutical review on BPC-157 summarised in 2026 that so far no completed phase II trial and no validated dosing scheme exist, and that the available clinical data comes from fewer than thirty people in uncontrolled pilot attempts.
How dangerous are peptides bought online?
The biggest risk is often not the substance itself, but what is actually in the vial.
An investigation in the Journal of Medical Internet Research bought semaglutide vials from illegal online sellers in 2024. The measured active ingredient content was 28 to 39 percent above the declaration, the actual purity was between 7.7 and 14.4 percent instead of the stated 99 percent, and bacterial endotoxins were found in all samples.
On top of that come unknown long term risks, missing tested sterility in injectable products and legal questions.
That is why my position here is clear: curiosity yes, self experiment with unregulated goods no.
Do peptides do anything for building muscle?
For the growth hormone releasers advertised online, such as CJC-1295 or Ipamorelin, there are no robust human trials on muscle growth, strength or performance that would justify use outside of research.
These substances are also in the focus of doping analytics: a detection method from the Institute of Biochemistry at the German Sport University Cologne explicitly lists CJC-1295 among the peptides banned in competitive sport.
What is well supported for building muscle sounds more boring and is cheaper: enough protein, progressive strength training, sleep and recovery.
What do peptides in skin creams do?
Cosmetic peptides such as Matrixyl, Argireline or the copper tripeptide GHK-Cu are meant to prompt the skin to build more collagen or to soften muscle tension in the face.
A systematic review on cosmeceuticals in light induced skin ageing rated the evidence for topical peptides as comparatively good next to other groups of actives.
The context matters: the trials are mostly small and short and often funded close to the manufacturer, and the effects are moderate.
A cream is not free of risk either. Contact allergies, redness and irritation do occur, especially around the eyes and on skin that is already damaged.
A cream can influence the skin surface favourably, but it is no substitute for sun protection, sleep and nutrition.
Why can most peptides not simply be swallowed?
Because your digestive system is built to take exactly that apart.
Stomach acid and enzymes split protein into ever shorter pieces until single amino acids or di- and tripeptides are left.
A review on food derived oligopeptides describes how the chains become systematically shorter during simulated digestion while their biological activity decreases.
That is why most peptide medicines are injected, and why with swallowed peptide products the question of uptake is always the first one to ask.
What does the topic of peptides have to do with supplements?
Two things.
First, some peptides are sold as supplements, collagen peptides for example, although legally and biologically they are something entirely different from an injectable research peptide.
Second, the same principle applies to peptides as to minerals and vitamins: they are players in control loops, not switches. Anyone who adds a signalling molecule from outside is intervening in a feedback system. The body answers, sometimes with a counter regulation.
That is the reason why I am even more careful with peptides than with micronutrients.
Where do I stand on peptides as a physician?
Curious and strict at the same time.
Peptide research is one of the most exciting fields in current medicine, and the GLP-1 receptor agonists show that impressively. At the same time I see people in my practice injecting substances from the internet whose content nobody knows.
My line: approved peptide medicines belong in a medical indication with a baseline finding, monitoring and an exit plan. Everything else belongs in trials, not in your own thigh.
That is not paternalism, that is weighing risk with incomplete data.
How this topic connects with the others
Supplement Guide
The overview of every topic in this cluster
Collagen peptides
The peptides people actually swallow
Essential amino acids
The letters peptides are made of
NMN and NAD boosters
The same question, a different class of substance
Hormone Guide
Why control loops come with feedback
Weight Loss Guide
Where GLP-1 actually lands clinically
Strength training from 40
The muscle lever with the best evidence
Fullness and protein
How your body regulates hunger by itself
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