In 1921, Frederick Banting and Charles Best extracted a substance from a dog’s pancreas that kept a diabetic dog alive. They called it insulin. It was a peptide — a short chain of amino acids — and it became one of the most important drugs in human history. A century later, another peptide called semaglutide is reshaping how we think about obesity, appetite, and the line between vanity and medicine.

Between those two milestones lies a story that touches everything this newsletter cares about: hard science, big capital, regulatory warfare, and the eternal human desire to be better than we are.

Peptides are everywhere right now.

Injected by tech founders in San Francisco. Promoted by influencers on TikTok. Debated in Senate hearings. Manufactured at scale by pharmaceutical companies making bets worth billions. The grey market for peptides imported from Chinese labs doubled in 2025. Robert F. Kennedy Jr. made peptide deregulation a political platform. Novo Nordisk and Eli Lilly are in an arms race to turn injectable peptides into pills.

This primer will explain what peptides are, why they work, what’s real and what’s hype, and what it all means for markets, technology, and the project of being human.

Part 1: What Peptides Are (And Why They Matter)

Your body runs on chemistry, and much of that chemistry is peptide-based.

A peptide is a short chain of amino acids — typically between 2 and 50 — linked together by peptide bonds. If amino acids are the alphabet, peptides are short text messages: brief, targeted, carrying specific instructions. Proteins are the complex molecular machines assembled from the same alphabet. The distinction isn’t just length — it’s role. Proteins build structures. Peptides carry orders.

Your body uses around 7,000 different peptides to regulate nearly everything: hunger, sleep, immune response, tissue repair, mood, inflammation, sexual function, pain. Pause on that number for a moment. Right now, as you read this sentence, peptides are telling your gut how to digest your last meal, instructing your immune system which cells to trust, modulating the neurotransmitters that sustain your attention on these words. You are, at this very moment, being coordinated by peptides.

Insulin is a peptide. So is oxytocin, the molecule behind bonding and trust. So are endorphins, the body’s painkillers. So is GLP-1, the gut hormone that tells your brain you’re full — and the molecule behind the biggest pharmaceutical category of the last decade.

The thing that makes peptides medically interesting is that they are signaling molecules. They bind to receptors on cell surfaces — often G-protein-coupled receptors, the same family targeted by roughly 34% of all FDA-approved drugs — and set off chain reactions: activating growth factors, modulating nitric oxide, shifting gene expression, redirecting immune responses. Short and specific, but capable of triggering consequences far larger than themselves.

That specificity matters. A single molecule of BPC-157 — one of the most discussed peptides in the biohacking world — is roughly 4 nanometers across, about 20,000 times smaller than the width of a human hair. Yet it carries enough structural information in its 15-amino-acid sequence to bind a specific receptor and initiate a cascade of tissue repair. A small molecule drug like aspirin or ibuprofen is a blunt instrument — it floods the system and hits many pathways at once. A peptide can be designed to engage one receptor, in one tissue, and trigger one response. Less collateral damage. Fewer side effects. More precision.

But peptides carry weaknesses that kept them on the margins of medicine for decades. They’re fragile: stomach acid destroys them, which is why most had to be injected. They have short half-lives — the body breaks them down in minutes. And for most of the 20th century, they were expensive and difficult to manufacture. Medically important, pharmacologically limited.

Before we talk about what changed, take a step back.

The body’s peptide signaling network — 7,000 molecules, each with a specific target, working in concert across every organ system simultaneously — is one of the most elegant communication architectures in nature. Evolution spent hundreds of millions of years refining it. We’ve spent about a century studying it. The ambition now is to learn the language well enough to write new messages. That’s either magnificent or reckless, depending on how much you trust the students.

What unlocked that ambition?

Three things, arriving roughly in sequence: synthetic chemistry got better, biology got cheaper, and artificial intelligence showed up.

The Peptide Primer

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