# Every Compound Here Began as Something the Body Already Makes > Primitive Peptides — Research Peptide Fundamentals: Endogenous Origins — Research Peptide Fundamentals research peptides traced to their endogenous parents: KPV, PT-141 (bremelanotide), GHK-Cu and NAD+, and where each manufactured version stops resembling the original. An independent literature digest; nothing is sold and no dose is advised. **RESEARCH PEPTIDE FUNDAMENTALS / ENDOGENOUS ORIGINS** A hormone fragment, a redesigned version of that same hormone, a sequence cut out of collagen, and a coenzyme every cell recycles — traced back to the original, then marked at the exact point where the manufactured version stops behaving like it. ### [NAD+](/nad) A coenzyme every cell already makes and recycles, not a peptide at all. Its tissue level falls with age, which is the entire rationale for the precursor supplements built around it — and the clearest case where raising a natural molecule and achieving an outcome turn out to be two different results. ### [KPV](/kpv) The last three amino acids of alpha-melanocyte-stimulating hormone, sold on its own. The fragment keeps the parent hormone's anti-inflammatory action and drops its pigment-driving action, and appears to work through a route the full hormone does not use at all. ### [PT-141](/pt-141) Bremelanotide: the middle of that same hormone, cyclised, substituted and stabilised until it survived long enough to become a prescription drug. Everything that makes it usable is a departure from the endogenous molecule it was drawn from. ### [GHK-Cu](/ghk-cu) A three-amino-acid sequence that sits inside type I collagen and is freed when collagen is broken down, presented to cells bound to a copper ion. Its age-linked decline is documented [21], but that observation does not establish a replacement strategy. ## Abstract, in plain English Peptides are short chains of amino acids — the same building blocks that make up proteins, just far fewer of them strung together. The body produces thousands of them and uses them as signals: a peptide fits a receptor, the receptor changes what a cell does, and the effect stops when the peptide is broken down. Four of the molecules discussed most often in peptide research did not begin in a laboratory. **KPV** is a three-amino-acid piece cut from the tail of a human hormone. **PT-141 (bremelanotide)** is a redesigned version of the middle of that same hormone. **GHK** is a sequence that sits inside collagen, the structural protein of skin and connective tissue, and is released when collagen is broken apart. **NAD+** is not a peptide at all but a coenzyme — a small helper molecule — that every living cell already builds and recycles. This site starts each entry at the original molecule and then marks the point where the manufactured version stops resembling it. That gap is the subject: fragment against whole hormone, engineered against native, applied on a schedule against released on demand. ## The name, and the error it invites *Primitive* in this masthead means **original** — first in the sequence, the thing that existed before the pharmacology built on top of it. It does not mean gentle, safe, better tolerated or more effective, and this desk treats any drift in that direction as an error to be corrected rather than a tone to be adopted. The reasoning the name invites is the naturalistic fallacy: the body makes it, therefore it must be harmless. Endogenous origin is a fact about a molecule's provenance. It is not a property the molecule carries into a vial, and it sets none of the variables that determine what a compound actually does — dose, route, concentration, schedule, and everything else the molecule touches on the way past its intended target. The evidence assembled here contradicts the fallacy at every entry. Bremelanotide is a close relative of a human hormone and is reported to darken skin, gums and moles with frequent repeated dosing, because the receptor family it was designed for also governs pigment [17]. Nicotinamide riboside raises whole-blood NAD+ by as much as 142% at the highest dose studied [5], and a 2025 review of the human trials still concluded that efficacy in ageing is limited and tissue-level data sparse [1] — the natural molecule went up, the outcome did not follow. GHK is a genuine human sequence whose central research problem is that it barely crosses intact skin at all [18]. An endogenous sequence delivered at a concentration and a rhythm the body never uses is a new pharmacological event. It is not a restoration, and the word *natural* does not survive the journey into a syringe or a serum bottle. ## What "research peptide" covers, and what it does not The phrase *research peptide* describes a market category, not a regulatory class, and the four compounds catalogued here occupy four different legal positions. Bremelanotide is an approved prescription pharmaceutical in the United States for one narrowly defined indication, with a published label specifying dose, pharmacokinetics and contraindications [17]; material sold online as "PT-141 research chemical" sits entirely outside that approval and outside any verification of identity, purity or concentration. KPV has no published human clinical trial of any kind — its whole efficacy literature is cell culture and rodent models, chiefly of colitis. Topical Copper Tripeptide-1 is a legal cosmetic ingredient in the United States, the European Union and the United Kingdom, while injectable or systemic GHK-Cu is an unapproved research chemical. NAD+ and its precursors are sold as dietary supplements, with the regulatory status of nicotinamide mononucleotide contested by the FDA on the grounds that it was first investigated as a drug. What unites them is not a legal category but a research literature — and, for three of the four, a documented parent molecule in human physiology. This desk summarises that literature. It sells nothing, prescribes nothing, arranges no supply, and states no dose for any person. ## Four origins, four different distances travelled Arranged by how far the manufactured version has moved from the original, the set covers almost the whole range. **KPV travels the shortest distance in structure and the longest in mechanism.** It is residues 11 to 13 of alpha-melanocyte-stimulating hormone, unmodified — the same three amino acids, in the same order, that terminate the natural hormone. Yet it retains anti-inflammatory activity while losing the pigmentary action of the parent [10], stays active in mice lacking the parent hormone's principal receptor [9], and is taken into gut cells through a transporter that handles di- and tripeptides only [8] — a doorway the intact 13-residue hormone cannot fit through. **PT-141 travels the furthest by design.** It is a cyclic heptapeptide analogue of the core of the same hormone, closed with a lactam bridge and substituted at two positions, and every one of those changes exists to defeat the rapid breakdown the endogenous molecule undergoes. **GHK-Cu keeps the sequence and changes the occasion.** The tripeptide occurs inside the alpha-2(I) chain of type I collagen and is liberated when tissue is injured and collagen is degraded — a local, event-driven release. A serum applied twice daily is a different event entirely, and plasma GHK falling from roughly 200 ng/mL at age 20 to about 80 ng/mL by age 60 [21] is a description of ageing, not a prescription for reversing it. **NAD+ does not travel at all.** The supplement and the endogenous molecule are the same compound, or a direct precursor of it, which is precisely why it is the sharpest test in the set: when identity is perfect and the level demonstrably rises, whatever fails to follow cannot be blamed on the molecule being unnatural. --- Primitive Peptides traces four research compounds back to the molecules the body makes on its own, and treats endogenous origin as a starting hypothesis rather than a safety claim — a literature digest, not a clinic, a vendor, or a source of dosing advice.