What Are Peptides?
Short chains, big effects
A peptide is just a short chain of amino acids — anywhere from 2 to about 50. Above 50 it's usually called a protein. The short length is why they can be injected (and sometimes absorbed sublingually) and why they act as precise biological messengers.
Your body already makes 7,000+
Insulin, glucagon, oxytocin, growth hormone, and every neuropeptide are all peptides your body produces naturally. "Peptide therapy" usually means giving you a synthetic copy of one, or a tweaked variant that lasts longer.
Match the peptide
Connect each well-known peptide to its primary role.
Why they're not pills
Peptides are fragile. Your gut digests them before they reach the bloodstream, which is why most are injected subcutaneously. A few (like semaglutide's oral form, Rybelsus) use absorption-enhancer tricks to survive the stomach.
Peptide vs protein vs small molecule
**Small molecules** (under ~50 atoms) — aspirin, statins, metformin — are tiny, cheap, oral. **Peptides** (2–50 amino acids) — semaglutide, oxytocin — are larger, more selective, usually injected. **Proteins** (50+ amino acids) — antibodies like Humira, growth hormone — are huge molecules requiring cold chain and complex manufacturing. Peptides sit in the sweet spot: selective enough to avoid off-target effects, simple enough to manufacture by chemical synthesis rather than living-cell production.
Counter-intuitive: more peptide is not better
Most peptide receptors **down-regulate** when over-stimulated — the receptor literally retracts into the cell. Push too much GLP-1 and the receptor density falls; push too much testosterone and your body's own production shuts down. This is why pulsatile dosing (with rest gaps) often outperforms continuous high-dose. The body's homeostasis machinery is older than any drug.
Which of these is a peptide therapy?
Tap each item to reveal what category it belongs to.
Tap each tile to reveal the detail.
The regulatory landscape
Of the ~80 peptide drugs FDA-approved as of 2023, the vast majority are for diabetes, oncology, or rare diseases. Many "peptides" sold for longevity or healing (BPC-157, TB-500, epitalon) are **not FDA-approved for human use** — they're sold as "research chemicals" or compounded by specialty pharmacies operating in a grey zone. The science can be promising; the supply chain is another matter. Source matters: contamination rates in unregulated peptides reach 30%+ in tested batches.
Key Takeaway
Peptides are short amino-acid chains — small enough to be precise, fragile enough to usually need injection. The category covers FDA-approved game-changers (insulin, GLP-1s, oncology peptides) and a grey-market world of research-grade compounds where source quality and dosing strategy matter at least as much as the molecule itself.
References
- Human Peptide Atlas — global catalogue of endogenous human peptides
- Oral semaglutide absorption via SNAC — PIONEER 1 trial
- GPCR desensitisation and internalisation — review
- Peptide therapeutics — landscape and clinical development