Part III — Growth and Repair Peptides

Chapters 14–19

This is the part of the book most likely to make someone angry.

Part II was comfortable. The evidence was excellent, the drugs were approved, the ratings were mostly ✅, and the honest complications — cost, access, discontinuation, muscle loss — were complications within a well-established picture.

Part III is different. Here the evidence thins out dramatically while the marketing gets much louder, and the gap between those two things is the widest anywhere in peptide science. This is where a compound with fifty rodent studies and zero human trials has a larger online following than a drug with a completed Phase III program. It is where clinics advertise "peptide therapy" for aging. It is where a molecule first used in racehorses is sold to weekend athletes as though veterinary use were a credential.

And it is where the book has to be most careful not to overcorrect.

The two failure modes this part avoids

The easy version of Part III would be a debunking. Sneer at the biohackers, point out that BPC-157 has no human trials, declare the whole space a scam, and move on. That version would be wrong, and it would be wrong in a way that helps nobody.

Because some of this is real. Growth hormone deficiency is a genuine condition and recombinant GH genuinely treats it. Tesamorelin is an FDA-approved growth hormone secretagogue for a specific indication, which means the mechanism these compounds share is not fictional. Thymosin alpha-1 is approved in a number of countries. The rodent literature on BPC-157 is not fabricated — it is, in several respects, genuinely impressive work. The people taking these compounds are not fools; they are, mostly, people with an injury that has not healed or a body that has stopped responding the way it used to, reading the only literature they can find.

The other easy version would be credulity: mechanism is plausible, the animal data looks good, thousands of people report benefit, so it probably works. That version is the one already available everywhere, and it is why this book exists.

Part III does the harder thing: it takes each compound's actual evidence seriously and says exactly where it stops.

The six chapters

Chapter 14 — Growth Hormone is the origin of this entire cultural phenomenon. A real hormone with real approved indications, a real age-related decline, and a twelve-person study from 1990 that launched a multi-billion-dollar anti-aging industry. The chapter reads that study carefully, notes the three things it did not measure, and issues two different ratings for one molecule.

Chapter 15 — Growth Hormone Secretagogues covers the indirect strategy: rather than injecting GH, stimulate your own pituitary to make more. CJC-1295, ipamorelin, GHRPs, MK-677, and tesamorelin. The central lesson here is one of the most useful in the book — "it raises growth hormone" is a mechanism claim, not an outcome claim, and the distance between them is where nearly all of this market lives.

Chapter 16 — IGF-1, Myostatin Inhibitors, and the Muscle-Building Peptides goes to the frontier of anabolic signaling, where the pharmaceutical industry has run real trials and mostly been disappointed. Compounds reliably increased muscle mass and did not reliably improve what patients could do. That dissociation — surrogate endpoint met, real endpoint missed — is the chapter's whole point, and it recurs everywhere in medicine.

Chapter 17 — BPC-157 is the book's central case study, and probably its most important chapter after Chapter 5. The animal data is presented at length and taken seriously. The human data is described accurately, which takes one sentence. Then the chapter does the hard work of explaining why those two facts coexist without contradiction, and what would have to happen to change the rating.

Chapter 18 — TB-500, Thymosin Alpha-1, and Other Recovery and Immune Peptides is where the distinctions get fine. TB-500 is marketed as thymosin beta-4 and is not the same molecule. Thymosin alpha-1 has approvals in some jurisdictions and not others, which is itself informative. "Immune modulation" turns out to be the vaguest claim in the field.

Chapter 19 — The Gray Market leaves the biology entirely. What is actually in the vial? Who made it? Under what controls? What has independent testing found? What does medical supervision provide that self-experimentation cannot — baselines, monitoring, dose adjustment, and someone to call at 2 a.m.? This chapter is not anti-peptide. It is pro-knowing-what-you-have.

For the reader who is already using something

Some of you are. That is fine, and it is not a reason to stop reading.

Part III will not tell you what to do. It will tell you what is known about what you are using, what is not known, which of the claims you were given are supported and which are not, and what a clinician could add that a forum cannot. Some readers will finish these chapters and stop. Others will finish and continue, having decided the uncertainty is acceptable to them. Both are informed decisions, and this book's job is to make sure the decision is informed rather than to make it for you.

What Part III asks is only this: read Chapter 5 first, and hold the compounds you are personally invested in to exactly the standard you would apply to a compound you had never heard of. That is much harder than it sounds. It is also the entire discipline.

📋 Your Evidence Dossier — Part III

Chapter 17 asks you to do the hardest thing in the project: write an honest ❌ on a compound you may have hoped would be a ✅. Not a dismissal — a precise statement of what the evidence supports, what it does not, and what would change your mind.

If you can write that entry cleanly, without softening it and without sneering, you have the skill this book was built to teach.

Chapters in This Part