What are peptides?

The short answer

Peptides are short chains of amino acids. Amino acids are the building blocks of proteins; chain a handful together and you have a peptide, chain hundreds and you have a protein. Your body is full of them — they're how cells signal each other to grow, heal, regulate metabolism, modulate hormones, and a hundred other functions. Most of them are doing this work right now without anyone thinking about them.

What people usually mean by "peptides" in the self-directed health context is a specific subset: synthetically produced peptides that mimic or modulate the body's own signaling — used to accelerate recovery, support growth hormone production, manage weight, improve cognition, or address specific health goals.

How peptides differ from supplements, hormones, and pharmaceuticals

Peptides sit in a category of their own, and the distinction matters:

• Supplements (vitamins, herbs, amino acids) work by adding to or supporting existing biochemical pathways. They're regulated as food products under DSHEA. Low specificity, broad availability, weak evidence requirements.
• Hormones (testosterone, thyroid, estrogen) are the body's high-level regulators. They're tightly regulated and almost always require a prescription.
• Pharmaceuticals are drugs designed to bind specific targets — anything from antibiotics to chemotherapy. Regulated under the FDA's drug-approval pathway; require clinical trials.
• Peptides are signaling molecules — much smaller and more targeted than hormones, much more specific than supplements, less broadly characterized than approved pharmaceuticals. Some peptides are FDA-approved drugs (semaglutide, tesamorelin); most peptides used by self-directed users are not.

The regulatory landscape

This is the part that confuses most people, so it's worth being precise. The U.S. peptide market splits into a few categories with different rules:

FDA-approved peptides

A small set of peptides have an FDA-approved indication and are available via prescription. Examples: semaglutide (Wegovy / Ozempic) for diabetes and obesity, tesamorelin (Egrifta) for HIV-associated lipodystrophy, sermorelin historically for growth hormone deficiency. Approved peptides can be prescribed on-label or, when a licensed practitioner decides it's clinically appropriate, off-label.

503A / 503B compounded peptides

State-licensed compounding pharmacies (503A) and federally-registered outsourcing facilities (503B) can compound peptides into patient-specific preparations under specific conditions — typically when an approved drug isn't available in the form the patient needs. Compounding is the most common legitimate pathway for getting non-mass-market peptides into a patient's hands with a prescription and a practitioner's oversight.

Research-use-only (RUO) peptides

A large category of peptides — BPC-157, TB-500, GHK-Cu, and many others — are sold by research-grade vendors under RUO labeling. Per regulatory labeling, these products are sold for laboratory and research purposes, not for human consumption. They are not FDA-approved for any human use, and the vendor that sells them is not a pharmacy.

Despite that labeling, research-grade peptides are widely used by self-directed peptide users. This isn't a fringe activity — it's a well-established community practice with its own conventions around sourcing, dosing, cycling, and safety. PepStakk's role is to help users navigate this informed: surface what vendors disclose, vet the disclosure for completeness and consistency, and connect Stakkers with licensed clinicians who can review their protocols.

The functional categories PepStakk uses

The Library organizes peptides by function — the categorical grouping for what a peptide does. The major ones:

Healing & Recovery

BPC-157, TB-500 (TB4 / TB-500), GHK-Cu, KPV. Tissue repair, anti-inflammatory effects, wound healing acceleration. The most widely-used category for general self-directed use, in part because the safety profile is well-characterized and the protocols are forgiving.

Growth Hormone Secretagogues

CJC-1295, Ipamorelin, Tesamorelin, Sermorelin. These don't add growth hormone directly; they prompt the pituitary to produce more of its own. Common stack pattern: a GHRH (CJC, Tesamorelin) paired with a GHRP (Ipamorelin, GHRP-2/6). Used for body composition, sleep quality, and recovery.

GLP-1 / Metabolic

Semaglutide, Tirzepatide, Retatrutide. The class that drove peptides into the mainstream news cycle. Approved pharmaceutical pathway is the safest route here — these are powerful drugs with real side-effect profiles, and clinical oversight matters.

Longevity

Epitalon, MOTS-c, Humanin, NAD+ precursors. Anti-aging mechanisms — telomere maintenance, mitochondrial function, cellular senescence reduction. The evidence base is mixed; some peptides have decades of Russian clinical-trial data, others are entirely preclinical.

Sexual Health

PT-141 (Bremelanotide), Melanotan II. PT-141 has FDA approval for hypoactive sexual desire disorder in pre-menopausal women; it's used off-label more broadly. Melanotan II is RUO; widely used despite known side effects.

Cognitive & Neuro

Semax, Selank, Cerebrolysin, Dihexa. Nootropic and neuroprotective claims. Most are Russian / Eastern European-origin; the evidence base in Western literature is limited.

Sleep / Repair / Recovery

DSIP, Pinealon. Niche category — used less commonly than the headline functions above.

What "research" looks like in this space

Peptide research splits into three tiers of reliability, which PepStakk's evidence tier framework grades:

• T1 — Human RCTs and systematic reviews. Gold standard. Mostly limited to FDA-approved peptides plus a handful of well-studied research peptides.
• T2 — Human observational or open-label trials. Useful but lower confidence than RCTs. The bulk of evidence for newer or less-commercial peptides.
• T3 — Animal models or preclinical mechanism studies. Demonstrates a mechanism; doesn't demonstrate human efficacy. Most peptide claims live here.
• T4 — Anecdotal or community-reported. Forum reports, podcast claims, vendor marketing. Useful for hypothesis generation; not evidence on its own.

When you see a peptide claim — "BPC-157 heals tendon injuries" — the right question is which tier the claim sits in. T1 means trust it. T3 means treat it as a hypothesis worth taking seriously. T4 means look for better sourcing before committing to a protocol.

Where to go from here

If you're considering peptide use, the responsible path is roughly this:

1. Understand what you're using and why. Don't assemble a stakk because a podcast told you to. Read about the function category, the specific peptide, and what evidence exists.
2. Source from suppliers you can audit. Read the COA. Check whether the lab is third-party. Look at the testing methodology. PepStakk's supplier directory does this vetting for you — but read the disclosures yourself.
3. Build a protocol that respects cycles. Most peptides need on-cycle / off-cycle windows. Continuous use of growth hormone secretagogues, for example, downregulates the pituitary's response.
4. Log what you take. Adherence matters. Dose drift matters. The Schedule tab in the PepStakk app is built for this.
5. Get clinician eyes on it when it matters. PepStakk's Clinician Network is built for async stakk reviews — informational, not a clinical relationship, but a real check against blind spots.