Lo que la gente pregunta — y cómo respondemos

A peptide is a chain of multiple amino acids — shorter than a protein. The boundary is fuzzy, but typically up to about 50 amino acids is called a peptide, above that a protein. Peptides occur endogenously (e.g. hormones like insulin or oxytocin) and are synthetically produced to mimic, enhance or study these actions.

Both consist of amino-acid chains. Peptides are shorter (commonly up to ~50 amino acids) and often lack pronounced 3D folding. Proteins are longer, fold into complex structures and thereby gain specific functions like enzymatic activity. The threshold is conventional, not biochemically hard — what matters more is whether the structure is independently functional.

Half-life (t½) is the time for an active substance's concentration in the body to fall to half. After 4–5 half-lives, around 94–97% is eliminated. This is a simplified model — real pharmacokinetics can be multi-phasic with different half-lives in plasma and tissues. When dosed repeatedly at intervals shorter than the half-life, the substance accumulates to a steady state.

Bioavailability is the proportion of an administered substance that reaches systemic circulation unchanged. A subcutaneous injection bypasses gastric acid and the liver's first-pass effect, which is why many peptides have high subcutaneous bioavailability (typically 70–95%). Oral administration is different — peptides are rapidly broken down in the digestive tract, so oral bioavailability is often in the single-digit percentage range. Rybelsus (oral semaglutide) uses an absorption enhancer (SNAC) to reach clinically relevant levels at all.

A GLP-1 receptor agonist is a class of substance that mimics the action of the body's own gut hormone GLP-1 (glucagon-like peptide-1) – hence the term incretin mimetic. These substances bind to and activate the GLP-1 receptor. Examples are semaglutide and tirzepatide; tirzepatide additionally acts at the GIP receptor (dual agonist). In clinical studies these substances were investigated chiefly in the context of blood-glucose regulation and body weight, and are approved by the FDA and EMA for type 2 diabetes and weight management. This description is neutral and mechanistic.

A peptide's molecular weight (also molar mass) is the sum of the atomic masses of all atoms in the molecule. It is usually given in daltons (Da) or grams per mole (g·mol⁻¹); one dalton equals one gram per mole. Molecular weight is a fundamental physicochemical property. Scientifically it matters for uniquely characterising a peptide, identifying it analytically (e.g. by mass spectrometry) and converting amounts of substance into mass. It also helps distinguish smaller peptides from larger proteins and is a fixed identifier in chemical databases.

Peptides and SARMs are chemically fundamentally different classes. Peptides are chains of amino acids linked by peptide bonds – biological molecules related to proteins. SARMs (selective androgen-receptor modulators), by contrast, are synthetic small-molecule compounds that have no peptide structure and act selectively at the androgen receptor. They therefore differ in both chemical structure and mechanism of action. This comparison is purely definitional and neutral; it judges neither class and contains no usage recommendation.

Amino acids are the molecular building blocks of peptides and proteins. Each has an amino group, a carboxyl group and a characteristic side chain that determines its properties. Humans use about 20 proteinogenic amino acids, which are genetically encoded and assembled into polypeptide chains. They are joined by peptide bonds, covalent bonds between the carboxyl group of one amino acid and the amino group of the next. The order of these amino acids (the sequence) determines which peptide or protein forms and how it folds in space. Amino acids are thus the fundamental structural unit of these classes.

An agonist is a molecule that binds to a receptor and activates it, triggering a cellular response much like the body's natural messenger. An antagonist also binds to the receptor but does not activate it; instead it blocks or dampens the receptor's signal. This distinction is central to peptide pharmacology: some peptides act as receptor agonists, such as GLP-1 receptor agonists, others as antagonists. Whether a substance activates or blocks determines its pharmacological mechanism. There are also partial agonists with attenuated effects and inverse agonists, which reduce a receptor's baseline activity.

Incretins are gut hormones released after eating that stimulate insulin secretion from the pancreas. The two most important are GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide). They contribute to the so-called incretin effect: orally ingested glucose triggers a stronger insulin response than the same amount given intravenously. Both are themselves peptide hormones. Incretins form the scientific basis for a drug class known as GLP-1 receptor agonists and dual GIP/GLP-1 receptor agonists, studied for type 2 diabetes and weight management.

Lyophilisation, commonly called freeze-drying, is a process in which a frozen substance is dried under vacuum. The frozen water passes directly from the solid to the gaseous state by sublimation, without becoming liquid. What remains is a dry, often powdery or cake-like material. Peptides are frequently supplied in this form because, as a dry solid, they are chemically far more stable and longer-lasting than in aqueous solution, where they can degrade more quickly. The term therefore describes only a physical preparation and preservation state of the substance, not a use.

The terms describe different things and often overlap. A peptide is a structural unit: a chain of amino acids linked by peptide bonds. A hormone, by contrast, describes a function: a messenger that carries a signal from one place in the body to another. Many hormones are chemically peptides, such as insulin or glucagon, which is why we speak of peptide hormones. Other hormones belong to different chemical classes, for example steroid hormones such as cortisol. Conversely, not every peptide is a hormone. In short: peptide denotes the blueprint, hormone the biological role, and the two categories can overlap.

Both are peptide substances but differ in their target receptors. Semaglutide is a GLP-1 receptor agonist: it binds to and activates the receptor for GLP-1. Tirzepatide is a dual receptor agonist that acts at both the GIP and the GLP-1 receptor. Both have been studied in clinical trials and are approved in several countries for type 2 diabetes and weight management, with the exact approval status varying by country. A detailed side-by-side of the two, including mechanism, evidence and legal status, is available on our comparison page. This description is neutral and contains no recommendation.

RCT stands for Randomised Controlled Trial. Participants are randomly allocated to treatment and control groups, ideally blinded. Randomisation reduces systematic bias, blinding minimises expectation effects. RCTs are considered the methodologically strongest form of clinical evidence for "does this substance work?" — when they are large enough, well conducted and independently funded. An RCT with 12 people is methodologically an RCT but statistically questionable.

Animals differ from humans across many dimensions: metabolism, genetics, immune system, organ size, lifespan, behaviour. A mouse ages in two years, a human in 80. Doses are usually converted in mg/kg — but this regularly overestimates effects in humans or underestimates adverse events. Historically, around 90% of substances that work in animal studies turn out to be not effective enough or too toxic in clinical development. Animal models are an important first step, not proof.

In vitro literally means "in glass" — experiments outside a living organism, usually in cell culture or a test tube. In vivo means "in the living" — in a whole organism, animal or human. In-vitro results show that a substance can in principle do something; in vivo shows whether it also happens in a body's complex system. Many in-vitro effects disappear in vivo because absorption, distribution, breakdown and competition with endogenous factors come into play.

p < 0.05 means: if the null hypothesis is true (no real effect exists), the observed result or a more extreme one would be expected by chance less than 5% of the time. This is NOT the probability that the hypothesis is true. This is NOT the effect size. A tiny, clinically meaningless difference can be "statistically significant" if the sample is just large enough. Conversely, a large effect can have p > 0.05 if the sample is small. Effect size + confidence interval are the more informative quantities.

Statistical significance says: the observed result is unlikely to have arisen by chance alone. Effect size says: how large is the difference actually. These are different questions. A tiny, clinically irrelevant difference can be statistically significant if the sample is large enough (e.g. 100,000 participants). A clinically meaningful effect can appear non-significant if the sample is too small. Informative studies report both: effect size with confidence interval PLUS p-value. Reading only "significant" misses half the information.

A 95% confidence interval is a range around the estimated effect size that, in repeated similar studies, would contain the true value 95% of the time. A narrow CI means: the estimate is precise. A wide CI means: high uncertainty. Example: HR 0.80, 95% CI 0.72–0.90 means — the estimated effect is a 20% reduction, and the true effect most likely lies between 10% and 28% reduction. The CI is more informative than the p-value because it expresses effect size AND precision in one number. If the CI includes 1.0 (for hazard ratios) or 0 (for differences), the effect is not statistically significant.

Under repeated dosing at intervals shorter than the half-life, a substance accumulates in the body — the concentration after each dose is higher than after the previous one. After roughly 4–5 half-lives, the system reaches steady state: input and elimination are in equilibrium, concentration only fluctuates around a mean. For semaglutide (t½ ≈ 7 days) this takes about 4–5 weeks. Before steady state, trough and peak levels are lower than later — this explains why some effects only become visible after weeks.

Like any biologically active substance, peptides can have adverse effects. For well-studied, approved peptides, side effects are documented in clinical studies and listed in the prescribing information; they differ by substance. For many so-called research peptides, by contrast, human safety data is limited or absent, so the side-effect profile is often unclear. This site reports documented observations with an evidence grade and explicitly flags missing data. The content is for educational purposes and does not replace medical advice.

A meta-analysis is a statistical method that summarises and quantitatively combines the results of several independent studies on the same question. By pooling many data points it can increase statistical power and estimate an overall effect across studies. Its strength depends on the quality of the included studies: if these are flawed or very different (heterogeneity), the overall result can also be biased. Well-conducted meta-analyses of randomised controlled trials are nonetheless regarded as particularly informative in the evidence hierarchy.

Peptides are made of amino acids, the same building blocks the digestive tract actively breaks down. In the gastrointestinal tract, enzymes called proteases cleave peptide bonds, and the stomach's acidic environment adds to the breakdown. As a result, orally ingested peptides often reach the bloodstream only in very small, barely measurable amounts, referred to as low oral bioavailability. There are, however, engineered exceptions: oral semaglutide, for instance, uses an absorption enhancer to enable uptake. Such formulations are demanding, which is why many peptides are not available as a tablet. This is a neutral explanation, not usage information.

Preclinical refers to the research phase that precedes studies in humans. It includes investigations in cell culture (in vitro) and animal models (in vivo in animals). These experiments serve to examine a mechanism of action, possible effects and safety questions before a clinical trial in humans begins. Importantly, preclinical results do not transfer directly to humans. Many effects observed in cells or animals are not confirmed in human studies or appear differently. That is why preclinical evidence is graded as weaker than human studies in our evidence-tier system, particularly compared with randomised controlled trials.

Off-label use is the use of an approved medicinal product outside its approved indication, dose or patient population. Example: semaglutide is approved as Ozempic for type-2 diabetes — whoever receives it without diabetes for weight loss is in off-label use (unless it is prescribed as Wegovy with an obesity indication). Off-label is not illegal, but responsibility shifts from manufacturer to the prescribing professional. Insurance and liability issues become more complex.

AMG = Arzneimittelgesetz (German Medicinal Products Act). Governs what counts as a medicinal product, who may produce, distribute and prescribe it, and what authorisation is required. HWG = Heilmittelwerbegesetz (German Therapeutic Products Advertising Act). Governs how medicinal products and therapeutic treatments may be communicated — advertising with healing claims, indications and comparisons is heavily restricted. Both laws directly affect the discussion of non-approved peptides: "X helps with Y" is practically prohibited for non-approved substances.

Compounding is the individual preparation of a medicinal product in a pharmacy, distinct from an industrially approved finished product. In the US this is regulated under 503A/503B of the FDA compounding framework. During shortages the FDA can temporarily permit compounding — as in 2023/24 for semaglutide and tirzepatide. Compounded products are subject to less stringent controls than approved medicinal products, which can lead to risks regarding identity, purity and sterility.

The World Anti-Doping Agency (WADA) is an international organisation coordinating anti-doping rules in organised sport. It publishes the annual Prohibited List — a list of substances and methods banned in competitive sport (and partly out of competition). Federations like IOC, FIFA, UCI have signed up to the WADA Code, which makes the list a standard reference beyond sport. Many peptides appear on this list even where they are not otherwise legally restricted.

The Black Box Warning (also Boxed Warning) is the strongest warning in an FDA prescribing information. It sits in a black-bordered box at the top of the product label and flags serious, potentially life-threatening risks. Semaglutide carries a boxed warning on thyroid C-cell tumours based on rodent studies — human relevance is not established, but the FDA called for caution regardless. A boxed warning does not necessarily mean the substance is dangerous — it means the regulator explicitly wants to draw attention to a potential risk.

FDA (U.S. Food and Drug Administration) is the U.S. federal agency for food and drug safety. EMA (European Medicines Agency) is the European counterpart, based in Amsterdam. Both decide on approval, indications and safety warnings. They operate in parallel and not always in agreement — the FDA can approve an indication that the EMA rejects (or vice versa). In Germany, BfArM (Federal Institute for Drugs and Medical Devices) complements at the national level; in Switzerland, Swissmedic.

It depends on the specific peptide and the country – there is no blanket answer. Some peptides are approved medicines and prescription-only (e.g. semaglutide). Others are unapproved, labelled as research chemicals, or in some countries restricted or banned. Legal status can also change over time. This site documents the status per peptide and per country, neutrally and with source plus check date, without judging it. This information is for educational purposes only and does not replace legal or medical advice.

The label “for research use only” marks a substance that is not approved or evaluated as a medicine for human use. It has not gone through a regulatory approval process for safety and efficacy in humans. In regulatory terms the label means the substance is intended for laboratory research and is not held to the quality, purity and safety standards of medicines. It is not a statement about effect and not a licence for use. This information is for educational purposes only.

Some peptides are approved as medicines by authorities such as the FDA or EMA for specific indications. Such medicines are usually classified as prescription-only because their safe use requires a medical diagnosis, monitoring and a benefit-risk assessment. Prescription status is a regulatory classification: it is meant to ensure that a physician reviews the indication, possible risks and interactions. Which peptides are affected varies by country and approval status. This explanation is general and for informational purposes only.

Three reasons. First: most catalogued peptides are not approved as medicinal products. A dosing recommendation for a non-approved substance falls under AMG/HWG in Germany and is simply not permitted — no matter how safe it appears. Second: the evidence often does not support it. For many peptides only animal models exist. Converting mg/kg from mouse to human is methodologically questionable — what works in animals can be ineffective or cause adverse events in humans. Third: responsibility. A dosing recommendation requires individual history, co-medication, pre-existing conditions, lab values — things only a professional in direct contact can assess. A public website cannot replace that without becoming irresponsible.

Every documented observation carries a visible evidence tier — from strong to weak: human RCT (randomised controlled trial), human trial (other human study, e.g. cohort), animal model, in-vitro (cell culture), preclinical (other preclinical), anecdotal (forum / experience reports), theoretical (only hypothesis, not established). The idea: weaker tiers are deliberately visible, not hidden. So a reader immediately sees whether a statement is "established in a 17,000-person RCT" or "frequently discussed in forums".

We aggregate structured data exclusively from open, established sources: PubMed and Europe PMC for study metadata, PubChem and ChEMBL for chemical identifiers (CAS, sequence, molecular weight), FDA / EMA / TGA / BfArM / Swissmedic for legal status, EU CosIng for cosmetic ingredients, WADA for doping status. Forums, vendor websites, influencer posts and bro-science sources NEVER enter our factual base. They can at best be explicitly marked as "anecdotal" with a clear note that no study support exists.

Unblinded self-reports are particularly prone to placebo, recall and confirmation biases. People remember positive experiences selectively, normalise neutral courses upward, and often omit adverse events. "It helped me" is not a scientific statement about efficacy — it is a statement about one person's perception. We explicitly mark such statements as "Anecdotal · Not supported by studies", because that is more honest than letting them look like evidence.

Each peptide page carries a visible “last reviewed on” date, so it is transparent when the content was last checked. The information draws on structured data and studies from defined, legitimate sources (such as PubMed, Europe PMC, PubChem, ChEMBL and regulatory publications) and is updated when new evidence appears. Statements about effects also carry an evidence grade indicating how well supported they are – from human studies down to purely theoretical hypotheses. Where robust data is missing, this is explicitly flagged rather than filling the gaps.

Reconstitution means dissolving a freeze-dried (lyophilised) powder in a liquid solvent to obtain a solution of a defined concentration. The concentration follows purely arithmetically from the mass of the powder divided by the volume of the liquid, usually given in mg/mL. This site provides a pure-math calculator for this that only converts quantities – like a pocket calculator. It is explicitly not a usage or dosing instruction, only an arithmetic illustration.

From a scientific standpoint, peptides are generally regarded as sensitive molecules. In freeze-dried (lyophilised) form they are usually more stable than in solution. Stability data describe that many peptides are light- and temperature-sensitive and remain stable longer when refrigerated and protected from moisture; in solution, stability typically declines faster. Actual stability depends strongly on the individual peptide and formulation. These statements describe general chemical principles for educational purposes and are not a usage instruction.

Each peptide page contains its own legal-status section with an interactive country map and a table. For each country it records the status – such as prescription-only, unapproved, research-only, restricted or unclear – each with a short, neutral explanation, source and check date. This makes it transparent how the status is classified for a given country and what that classification is based on. The presentation is purely factual. It does not replace legal advice, and the applicable national law is always decisive.