A peptide is a signal, not a fuel
A peptide is a chain of amino acids — somewhere between 2 and 50 of them. Your body uses thousands of peptides every day as messengers between cells. Insulin is a peptide. Oxytocin is a peptide. Glucagon is a peptide. They tell specific receptors to do specific things.
That's the whole concept. Peptides do not provide energy, they do not build tissue directly, they do not act on every cell. They are signals — narrow, specific, and short-lived.
Why the category exploded
Three things happened at once. First, manufacturing got cheap enough that compounds that used to cost $10,000 a vial in research catalogs are now produced at consumer scale. Second, GLP-1 class peptides — semaglutide, tirzepatide, retatrutide — produced clinical fat-loss results that made the entire category mainstream. Third, the regulatory frame is patchy. Some peptides are FDA-approved drugs (Ozempic, Mounjaro, Sermorelin). Some are research-use-only compounds being sold under that label. Some are gray-market entirely.
The result is that "peptides" is now a wide category covering a $100 prescription glucose drug and a $30 vial of a research-only compound, and the consumer has to figure out which is which.
What separates a peptide from related compounds
Steroids (anabolics) are derivatives of testosterone or other hormones. They modulate gene transcription broadly across many tissues. Peptides do not. A peptide tells a specific receptor on a specific cell type to do one thing. That's why peptides have narrower side-effect profiles than steroids — they're not promiscuous.
SARMs (selective androgen receptor modulators) are non-peptide molecules designed to bind androgen receptors selectively. They are oral, they are not peptides, and they have their own distinct safety profile.
Supplements (vitamins, amino acids, herbal compounds) act broadly on metabolic substrates. They feed reactions. Peptides do not feed reactions, they trigger them.
Hormones can be peptides (insulin, glucagon, growth hormone) or steroids (testosterone, cortisol). The peptide hormones are the ones most often used as "peptides" in this scene.
Categories of peptides you'll actually encounter
- Healing: BPC-157, TB-500. Used for tendon, ligament, gut.
- Growth hormone class: Tesamorelin, Sermorelin, CJC-1295, Ipamorelin, MK-677. Stimulate endogenous GH release.
- Fat loss / GLP class: Semaglutide, Tirzepatide, Retatrutide. Suppress appetite, slow gastric emptying, improve insulin sensitivity.
- Cognitive / longevity: Selank, Semax, Cerebrolysin, Epitalon.
- Sexual / aesthetic: PT-141, Melanotan-1, Melanotan-2, GHK-Cu.
- Recovery / endurance: BPC-157 (cross-listed), AOD-9604.
The full index is at /peptides — every entry has a documented dose range, FDA status, WADA status, side effects, and the studies that exist (or don't).
Why "research use only" is on most labels
A peptide in the consumer market is usually one of three things: 1. An FDA-approved drug (semaglutide as Ozempic / Wegovy, sermorelin as a compounded prescription). 2. A compounded medication prepared by a 503A or 503B compounding pharmacy under specific federal rules. 3. A research-use-only chemical sold under that designation, with the buyer assuming all responsibility for what they do with it.
Most of what people buy online is in category 3. The "research use only" label is what makes the sale legal under current chemistry-supply rules. What buyers do after the sale is on them.
What Pepdex doesn't tell you
We don't recommend vendors. We don't share discount codes. We don't tell you where to buy. That's the line we keep so the site isn't a procurement guide. What we do is document what each compound is, what the research says, what dose ranges show up in protocols, what side effects to watch for, and what regulatory status applies. The rest is your call.
Where to go next
- Are peptides safe? An honest answer. — the actual safety landscape.
- The 65 peptides we cover — the full index.
- Beginner walkthrough — zero-to-first-cycle.
- FDA and WADA status explained — what each label actually means.
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