This is an educational explainer, not medical advice. Specific peptide protocols vary widely in evidence base, regulatory status, and safety profile. Talk to a licensed provider before using any peptide.
A peptide is a short chain of amino acids. That's the entire definition — but it leaves out the parts that actually matter for anyone trying to understand why so many of them are showing up in medicine, research, and the wellness industry at the same time.
This post covers what a peptide is at the molecular level, what separates it from a protein, how peptides are administered, and the single most important regulatory distinction for anyone considering using one: FDA-approved peptide drugs vs research peptides.
A peptide is a chain of amino acids
Amino acids are the alphabet of biology. There are 20 of them, and they get linked together via a chemical bond called a peptide bond (a covalent connection between the carboxyl group of one amino acid and the amino group of the next).
- Two amino acids joined → a dipeptide
- A handful → an oligopeptide
- A short chain (typically up to ~50 amino acids) → a peptide
- A larger chain that folds into a 3D structure → a protein
The boundary between "peptide" and "protein" isn't crisp — different sources put it anywhere from 30 to 100 amino acids. The practical distinction for medicine: peptides are short enough to be synthesized chemically (or in bacteria), and they typically signal — they tell cells to do things — rather than carry out structural functions themselves.
Why peptides are usually injected
Almost every peptide on this site is administered by subcutaneous injection — a small needle just under the skin. The reason: peptides are made of amino acids, and amino acids get digested by the same enzymes your body uses to break down protein in food.
Take semaglutide as the canonical example. It's a peptide drug. There are two FDA-approved versions:
- Ozempic®, Wegovy® — once-weekly injection
- Rybelsus® — daily oral tablet
The oral version requires a special absorption-enhancer (SNAC — sodium N-(8-[2-hydroxybenzoyl]amino)caprylate) to get past the stomach intact. Even so, only a small fraction of the dose actually makes it into the bloodstream. The injection version is far more bioavailable — by orders of magnitude.
This is why most peptide protocols are injected. It's not preference; it's chemistry.
Peptides are signaling molecules
The role peptides play in biology is mostly signaling. They tell cells what to do.
A few examples of well-studied peptide signals:
- Insulin — tells cells to take up glucose. (Technically a small protein, but historically grouped with peptides.)
- GLP-1 — your body's natural appetite-and-glucose regulator, released by gut cells after a meal. Semaglutide and tirzepatide are synthetic, longer-acting versions of this signal.
- Oxytocin — implicated in social bonding and uterine contraction.
- BPC-157 — a fragment of a protein found in gastric juice; studied for tissue-repair signaling.
This is why the same molecular class produces such different effects: GLP-1 agonists act on appetite, GHK-Cu acts on skin remodeling, ipamorelin acts on growth-hormone release. Different peptides talk to different receptors.
The categories you'll see
Loosely, the peptides covered on this site fall into 13 categories:
| Category | Examples |
|---|---|
| GLP-1 agonists | Semaglutide, Tirzepatide, Retatrutide, Liraglutide |
| Healing | BPC-157, TB-500 |
| Growth hormone (GHRP / GHRH) | Ipamorelin, CJC-1295, Sermorelin, Tesamorelin |
| Muscle / myostatin pathway | Follistatin-344, IGF-1 LR3, ACE-031 |
| Nootropic | Semax, Selank, Cerebrolysin, Dihexa |
| Sleep | DSIP |
| Immune | Thymosin α-1, LL-37 |
| Longevity | Epithalon |
| Cellular | NAD+, SS-31, Glutathione |
| Hormonal | Kisspeptin-10, Oxytocin |
| Cosmetic | GHK-Cu |
| Sexual | PT-141, Melanotan II |
| Metabolic | MOTS-c, AOD-9604 |
Each category has its own typical dose range, route of administration, side-effect profile, and clinical evidence base. The peptide library has a per-compound page for each.
The single biggest distinction: regulatory status
This is the part most consumer information sources skip, and it's the most important.
Peptides on the market split into two completely different categories:
FDA-approved peptide drugs
These have an official label, a defined indication, manufacturer quality control, and prescribing information published on DailyMed. The list is short:
- Semaglutide (Ozempic®, Wegovy®, Rybelsus®)
- Tirzepatide (Mounjaro®, Zepbound®)
- Liraglutide (Saxenda®, Victoza®)
- Insulin and its variants
- A handful of less-discussed compounds (e.g., teriparatide for osteoporosis, oxytocin for obstetric use)
For these compounds, the authoritative source for dosing is the FDA-approved label. The label tells you the indication, the contraindications, the side effects observed in trials, and the titration schedule.
Research peptides
This is everything else on this site — BPC-157, TB-500, ipamorelin, CJC-1295, retatrutide, GHK-Cu, MOTS-c, and the rest. These are not FDA-approved for human use. They exist in three forms:
- Research-only — sold to research institutions for in-vitro studies. The dominant legal channel.
- Compounded by a licensed pharmacy — under the supervision of a prescribing provider, for an individual patient. This is the legal path for human use.
- Sold by unregulated suppliers as "research peptides" — often marketed online with disclaimers like "for research use only, not for human consumption." The disclaimer is legally meaningful; the product is not held to the same quality standards as a compounded or approved drug.
For research peptides, the authoritative source for dosing is the peer-reviewed research literature on PubMed — not a forum, not a Reddit thread, not an Instagram post. Even the literature is often limited to animal models for many compounds.
The resources page lays out the database links for both categories.
Why peptides need a calculator
Most peptide doses are in the microgram-to-milligram range, and the vials ship as a freeze-dried powder you reconstitute yourself with bacteriostatic water. This produces three places where arithmetic errors become dosing errors:
- Concentration — vial mg ÷ BAC water ml = mg/ml
- Volume — target dose mg ÷ concentration = ml to draw
- Units — volume × syringe units/ml (100 for U-100) = the number on the syringe
A decimal-place mistake or a mg-vs-mcg confusion can mean a 10× or 1000× dosing error. The whole point of this site's reconstitution calculator is to remove that mental math from the dose-prep workflow.
Bottom line
A peptide is a short amino-acid chain that signals between cells. Most are injected because the digestive tract destroys them. The ones you can verify dosing for via an official label are a short list (the GLP-1 family plus a few others); everything else relies on peer-reviewed research and a prescribing provider.
If you want to start anywhere on this site, start with the reconstitution calculator — it's the single most-used utility, and it works without any account or signup. From there, the peptide library gives you a reference page for each compound.
Related reading
- Resources page — where the dosing data on this site comes from
- Reconstitution calculator — the free web tool
- Peptide library — 44 reference pages
- Protocol templates — 36 multi-phase ramps
References
- MedlinePlus: how genes make protein — basic biology background
- DailyMed — FDA-approved drug labels
- FDA: Compounded drug products — regulatory status of compounded peptides