§ Peptides
A Field Guide
Vol. I · MMXXVI
A plain-english survey — no marketing, no miracle cures

Peptides a field guide

Short chains of amino acids. Some heal tissue, some tune receptors, some do very little. The internet treats them like magic. This does not.

Contents Seven chapters
Specimens Six featured
Stance Evidence-first
Begin reading
§ 01

What, precisely, is a peptide?

A peptide is a short chain of amino acids linked by covalent bonds — the same chemistry that builds every protein in your body, just at a smaller scale. The convention is fuzzy, but most biochemists call anything under about fifty residues a peptide. Above that, you call it a protein.

Every one of the twenty canonical amino acids has the same backbone — an amino group on one end, a carboxyl on the other, a central carbon holding a unique side chain. When two amino acids meet, water leaves and a peptide bond forms. Do this a handful of times and you've built a signalling molecule. Do it hundreds of times, you've built an enzyme.

The short length matters. Small peptides slip through membranes, fold quickly, bind receptors with precision, and — when their job is done — break apart just as easily. That disposability is the point: they ferry signals, trigger cascades, and get recycled.

§ 02

The mechanism, in three movements

  1. i.

    Binding

    A peptide finds its receptor — a specific protein on the cell's surface — and latches on. The receptor's shape dictates which peptides it will accept; the fit is as specific as a key in a lock. Nothing else has happened yet.

  2. ii.

    Signalling

    Binding changes the receptor's shape, which triggers a chain of events on the cell's interior — G-proteins activate, enzymes switch on, second messengers flood the cytoplasm. The peptide itself stays outside; it only delivered a message.

  3. iii.

    Response

    The signalling cascade changes what the cell is doing — genes transcribed, proteins made, enzymes unleashed, structures built. Minutes to hours later, you see the effect: tissue heals, appetite shifts, skin remodels, sleep deepens. Then the peptide is cleared, and the system resets.

§ 03

Five rough territories

01

Therapeutic

Peptides that treat named conditions with real clinical trials behind them. Insulin. GLP-1 agonists. Oxytocin. FDA-approved bremelanotide.

02

Repair & Regeneration

The muscle-and-tendon class. BPC-157, TB-500, thymosin. Rich in animal data, thin on rigorous human trials, popular with athletes.

03

Growth-Hormone Secretagogues

Peptides that nudge the pituitary into releasing growth hormone — ipamorelin, sermorelin, CJC-1295. Effects real, marketing noisier than the evidence.

04

Neuropeptides

Signals aimed at the nervous system. Semax, Selank, oxytocin. Russian labs have decades of clinical use; the West is slower to catch up.

05

Cosmetic

Skin-surface peptides — GHK-Cu, Matrixyl, argireline. Mostly topical, with better evidence than the average marketed supplement.

§ 04

Six specimens, honestly described

Each card lists the peptide, its sequence, its claimed effect, and — the part most sites skip — the evidence tier and a plain note about what the evidence actually shows.

Specimen 02

GHK-Cu

Copper Tripeptide
Sequence
Gly-His-Lys + Cu²⁺
Length
3 residues + copper
Mass
340.4 Da
Origin
Isolated from human plasma, 1973

Claimed effect

Stimulates collagen synthesis, improves skin texture, accelerates wound healing. The old-guard cosmetic peptide.

Evidence tier Human trials · Cosmetic only

Honest note

Among the best-supported peptides for topical use — decades of research, multiple independent groups, real cosmetic studies. Claims beyond skin (systemic anti-aging, organ repair) are extrapolated from in-vitro work and should be treated skeptically.

Specimen 03

TB-500

Thymosin β4 Fragment
Sequence
LKKTETQ (partial)
Length
7 residues
Mass
889 Da
Origin
Synthetic fragment of a 43-residue protein

Claimed effect

Tissue repair, cell migration, angiogenesis. Borrows reputation from the full thymosin β4 molecule (which has real research).

Evidence tier Animal · Fragment confusion

Honest note

Fragment does not equal parent molecule. Most TB-500 claims rely on evidence for full-length thymosin β4. The fragment itself has much thinner support. Watch for marketing that quietly swaps the two.

Specimen 04

Epithalon

Epitalon / AEDG
Sequence
Ala-Glu-Asp-Gly
Length
4 residues
Mass
390.4 Da
Origin
Synthesized at St. Petersburg, 1980s

Claimed effect

Activates telomerase, extends lifespan, restores circadian rhythm. The anti-aging peptide with the boldest claims.

Evidence tier Animal · Single lab

Honest note

Nearly all positive data comes from Vladimir Khavinson's St. Petersburg group. Strong claims — lifespan extension, telomere elongation — with no replication outside Russia. Treat with the same skepticism you'd give any single-lab story.

Specimen 05

Semax

ACTH(4-10) analog
Sequence
Met-Glu-His-Phe-Pro-Gly-Pro
Length
7 residues
Mass
813.9 Da
Origin
Russian Academy of Sciences, 1980s

Claimed effect

Cognitive enhancement, stroke recovery, neuroprotection. Intranasal use; approved in Russia as a clinical drug.

Evidence tier Clinical · Geographic split

Honest note

Strongest clinical base of any peptide on this page — decades of Russian hospital use, real stroke-recovery trials, established safety profile. Western replication is thin, regulatory status outside Russia is nonexistent. Evidence is real, jurisdiction limited.

Specimen 06

PT-141

Bremelanotide · Vyleesi
Sequence
Ac-Nle-Asp-His-D-Phe-Arg-Trp-Lys-OH
Length
7 residues
Mass
1,025.2 Da
Origin
Palatin Technologies, 2000s

Claimed effect

Increases sexual arousal via central melanocortin receptors. FDA-approved for premenopausal HSDD as Vyleesi.

Evidence tier FDA-approved · Phase III trials

Honest note

The only specimen on this page with full regulatory approval and multiple independent Phase 3 trials. Mechanism is well-mapped. Side effects are real — nausea, hypertension, skin darkening at injection site. Effect is modest but statistically reliable.

§ 05

How to read the evidence

Not all evidence counts equally. A good habit — before trusting any peptide claim — is to find the strongest study actually cited and ask where on the pyramid below it sits.

Most peptide marketing cites in-vitro work or animal studies and leaves readers to assume those results would translate to a human. They often don't. The higher on the pyramid, the more confident you can be.

The peptides on the previous page sit everywhere on this pyramid. Bremelanotide is tier I. Semax is tier II. BPC-157, TB-500, and Epithalon sit at tier IV — and the single-lab asterisk means you should discount them further.

  1. I Meta-analysis · Phase III RCTs
  2. II Phase II · independent clinical
  3. III Small human trial · cohort
  4. IV Animal studies
  5. V In vitro · hypothesis
  6. VI Marketing copy · testimonial
§ 06

A short list of cautions