What are peptides?

Signalling, not building

Most of the peptides you will read about here act as signals rather than structural material (see peptides, proteins and amino acids). They bind receptors and instruct cells: release a hormone, migrate to a wound site, produce more collagen. The instruction is the function, which is why a very small quantity can have an effect out of proportion to its mass, and why purity, set by how peptides are synthesised, matters.

It is also why receptor selectivity matters so much (see receptor targets explained). A peptide that binds one receptor does one thing; a peptide that binds three does three, whether or not all three were wanted.

Four things the word does not tell you

The word peptide describes a molecular structure. It does not tell you the product type, the route into the body, the quality of the evidence, or the legal status. The same amino-acid sequence can appear in a face cream, a protein powder and an injectable, and those are different products under different rules. When we describe a compound, we keep four questions separate.

Cosmetic, collagen and injectable peptides

Three categories are confused most often because they share the word.

The evidence for cosmetic and oral skin peptides is real but narrow. Nukaly and colleagues (2026) pooled nineteen randomised trials with 1,341 participants and found improved hydration and brightness, a modest pooled effect on wrinkles, and inconsistent results for elasticity. Those are appearance endpoints measured in creams and oral products. They say nothing about an injected compound.

GHK-Cu is the clearest example. The copper tripeptide appears in serums at cosmetic concentrations and, in our range, as GHK-CU 50, a pre-loaded pen. Same molecule, different product, different route, different evidence.

The three categories also sit under different law. Cosmetics fall under the EU Cosmetics Regulation, collagen powders under food law, and the injectable compounds we sell are not authorised medicines in the EU. Why these compounds are not EMA-authorised explains what that means in practice.

Why most peptides are injected rather than swallowed

Peptides are chains of amino acids, and the digestive system exists to break exactly those chains down. Wang and colleagues (2024) list the barriers an oral peptide has to survive: stomach acid, pepsin, trypsin and chymotrypsin, the mucus layer and the gut wall itself. Getting a bioactive peptide through all of that takes deliberate formulation work such as permeation enhancers, liposomes or nanoparticles, and that engineering is the product rather than an incidental property. Without it, a swallowed peptide mostly arrives as amino acids.

Injection under the skin bypasses digestion, which is why the EMA guideline notes that most medicinal products containing synthetic peptides are for parenteral use. It also means the whole molecule is delivered, so sterility and cold-chain handling matter in a way they do not for a cream.

Traditionally that meant a vial of freeze-dried powder to be reconstituted before use. Our pens are different: each is a 3 ml multi-dose pen with the peptide already in solution, so there is no mixing step. Pen versus vial compares the two formats and reconstitution and why pens skip it explains what the solution format removes. The container changes the handling; it does not change what the peptide is or what evidence supports it.

What we sell and how it is checked

Our range is ten pre-loaded pens, listed in our pen catalogue: MOTS-c, tirzepatide, Melanotan II, retatrutide in two strengths, NAD+, a combined BPC-157 and TB-500 pen, GHK-Cu, a combined CJC-1295 and ipamorelin pen, and tesamorelin. Each is 3 ml with the peptide already in solution, and each ships with eight pen needles, a printed guide and a verification sticker. Bulk pricing applies automatically at checkout: 10% off at five pens and 15% at ten, pooled across compounds.

Every batch is tested by an independent laboratory before release: identity by mass spectrometry, purity by HPLC, and sterility. The certificate for your exact batch opens when you scan the QR code on the pen, and every certificate is published as a plain PDF at our certificate index with no account needed. What third-party testing means explains what each of the three tests shows. A certificate tells you what is in the pen. It does not tell you what the compound will do, which is a question only the published evidence for that compound can answer.

Pens travel at 2–8 °C in insulated packaging with a cooling element and a temperature indicator, from our Czech dispatch point to your refrigerator (cold-chain shipping has the detail). Prices are visible to everyone; buying requires an account and the short eligibility quiz.