What Are Peptides? A Beginner's Guide to Peptide Therapy

You've probably heard the word "peptides" more in the last two years than in your entire life before that. They're showing up in biohacking podcasts, longevity clinics, skincare products, fitness forums, and increasingly in mainstream health conversations. Semaglutide — the peptide behind Ozempic and Wegovy — became one of the most prescribed drugs on Earth.

But most coverage either oversimplifies ("peptides are miracle molecules") or overcomplicates things with biochemistry jargon. This guide is the middle ground: what peptides actually are, how they work in your body, which ones people are talking about, and what you should know before going deeper.

What Is a Peptide?

A peptide is a short chain of amino acids — the same building blocks that make up proteins. The difference between a peptide and a protein is essentially size:

Amino acids are individual molecular units (there are 20 standard ones in human biology)
Peptides are chains of 2 to ~50 amino acids
Proteins are chains of 50+ amino acids, often hundreds or thousands

Your body uses peptides as signaling molecules — chemical messengers that tell cells what to do. Insulin (51 amino acids) regulates blood sugar. Oxytocin (9 amino acids) affects bonding and mood. Endorphins (up to 31 amino acids) modulate pain. These are all peptides your body produces naturally.

The key insight: peptides aren't drugs in the traditional sense. They're molecules your body already recognizes and uses. Therapeutic peptides work by mimicking, enhancing, or supplementing these natural signaling pathways.

How Peptides Work

Peptides function through receptor binding. Like a key fitting into a lock, a peptide binds to a specific receptor on a cell's surface (or inside the cell), triggering a biological response.

Different peptides bind different receptors, which is why they have such diverse effects:

GLP-1 receptor agonists (semaglutide, tirzepatide) bind receptors in the pancreas and brain to regulate blood sugar and appetite
Growth hormone secretagogues (ipamorelin, CJC-1295) bind receptors in the pituitary gland to stimulate natural growth hormone release
Melanocortin receptor agonists (PT-141, melanotan II) bind melanocortin receptors affecting skin pigmentation and sexual function
Tissue repair peptides (BPC-157, TB-500) modulate growth factors and cellular repair processes

The receptor specificity is what makes peptides interesting compared to broad-acting drugs. A well-designed peptide targets a specific pathway without affecting unrelated systems — at least in theory. In practice, many receptors exist in multiple tissues, so side effects can still occur.

Categories of Peptides

The peptide landscape can feel overwhelming. Here's how to organize it by function.

Healing and Recovery Peptides

These are the peptides most associated with tissue repair, injury recovery, and regeneration.

BPC-157 is the most widely discussed healing peptide. Derived from a protein in human gastric juice, it has shown remarkable tissue repair properties in preclinical studies — accelerating tendon healing, protecting the GI tract, and modulating growth factors involved in repair. It's one of the few peptides stable enough for oral administration. Read our full BPC-157 guide →

TB-500 (Thymosin Beta-4 fragment) promotes cell migration to injury sites through actin regulation. It's commonly stacked with BPC-157 for the "Wolverine Stack" — complementary mechanisms targeting different aspects of the healing cascade. Read more about TB-500 →

Weight Loss and Metabolic Peptides

This category has seen the most mainstream attention, driven by the GLP-1 revolution.

Semaglutide (the peptide in Ozempic and Wegovy) targets GLP-1 receptors to regulate appetite, blood sugar, and satiety. It's FDA-approved for both type 2 diabetes and chronic weight management, backed by extensive Phase 3 clinical trial data showing 15-17% body weight reduction. Read more →

Tirzepatide (Mounjaro, Zepbound) is a dual GLP-1/GIP agonist — it targets two receptors instead of one. Clinical trials showed even greater weight loss than semaglutide (up to 22.5% body weight reduction in the SURMOUNT trials). Read more →

Retatrutide is a next-generation triple agonist (GLP-1/GIP/glucagon) in Phase 3 trials that showed up to 24% body weight reduction in 48 weeks. If approved, it could surpass tirzepatide. Read more →

Growth Hormone Peptides

Rather than injecting growth hormone directly, these peptides stimulate your pituitary gland to produce more of its own GH.

Ipamorelin is a selective growth hormone secretagogue that triggers GH release without significantly affecting cortisol or prolactin — making it one of the "cleanest" GH-stimulating peptides. Read more →

CJC-1295 is a growth hormone-releasing hormone (GHRH) analog that extends the duration of GH pulses. It's most commonly used in combination with ipamorelin — the "Ipamorelin + CJC-1295 stack" is the most popular GH peptide protocol. Read more →

MK-677 (Ibutamoren) is technically not a peptide — it's a small molecule growth hormone secretagogue — but it's always discussed alongside GH peptides because it serves the same function. Its main advantage is oral bioavailability. Read more →

Anti-Aging and Longevity Peptides

Epitalon is a tetrapeptide studied for its potential effects on telomerase activation — the enzyme that maintains telomere length. Telomere shortening is associated with aging, and epitalon has shown telomerase-activating effects in cell culture and some animal models. Read more →

GHK-Cu (copper peptide) is a naturally occurring tripeptide that declines with age. It stimulates collagen production, promotes wound healing, has anti-inflammatory effects, and has shown ability to upregulate regenerative genes while suppressing inflammatory ones. Read more →

MOTS-c is a mitochondrial-derived peptide involved in metabolic regulation and exercise physiology. It activates AMPK — a central energy-sensing pathway — and has been shown to improve exercise capacity and metabolic function in animal models. Read more →

Cognitive and Mood Peptides

Semax is a synthetic analog of ACTH(4-10) developed in Russia for cognitive enhancement. It modulates BDNF (brain-derived neurotrophic factor) and has been approved in Russia for stroke recovery, cognitive disorders, and immune support. Read more →

Selank is an analog of the naturally occurring immunomodulatory peptide tuftsin. It has anxiolytic (anti-anxiety) effects and modulates GABA neurotransmission. Like Semax, it's approved in Russia and typically administered intranasally. Read more →

Dihexa is a hexapeptide studied for its potent effects on hepatocyte growth factor (HGF), a pathway involved in memory formation. In animal studies, it showed cognitive-enhancing effects at remarkably low doses. It remains strictly a research compound. Read more →

Immune Peptides

Thymosin Alpha-1 is a 28-amino acid peptide naturally produced by the thymus gland. It plays a central role in T-cell maturation and immune regulation. It's approved in several countries (marketed as Zadaxin) for hepatitis B and C treatment, and it's used off-label for immune support. Read more →

LL-37 is a cathelicidin antimicrobial peptide — part of your innate immune system's first line of defense against pathogens. It has broad-spectrum activity against bacteria, viruses, and fungi. Read more →

KPV is a tripeptide fragment of alpha-MSH (alpha-melanocyte-stimulating hormone) with potent anti-inflammatory properties. It's being studied for gut inflammation and has shown effects in colitis models. Read more →

How Peptides Are Administered

Different peptides require different delivery methods based on their molecular properties.

Subcutaneous Injection

The most common method for research peptides. A small insulin syringe delivers the peptide just under the skin — typically in the abdomen, thigh, or upper arm. Most people find it nearly painless with 29-31 gauge needles.

Peptides that typically use SubQ injection: BPC-157, TB-500, ipamorelin, CJC-1295, growth hormone peptides.

Oral Administration

Most peptides are destroyed by stomach acid and digestive enzymes, making oral delivery ineffective. The exceptions are peptides specifically designed for oral stability:

BPC-157 is naturally acid-stable (derived from a gastric protein)
Semaglutide has an oral formulation (Rybelsus) engineered with an absorption enhancer
MK-677 is a small molecule, not a peptide, and is orally bioavailable by nature

Intranasal

Certain peptides — particularly those targeting the brain — use nasal spray delivery. The nasal mucosa provides a path that partially bypasses the blood-brain barrier.

Intranasal peptides: Semax, Selank, oxytocin.

Topical

Some peptides are used in skincare formulations applied directly to the skin. Penetration depends on molecular size and formulation.

Topical peptides: GHK-Cu, Argireline (Acetyl Hexapeptide-3), Matrixyl.

What You Need to Know About Safety

Peptides are not universally safe. Here are the critical principles.

The Evidence Spectrum

Not all peptides have the same level of evidence behind them.

FDA-approved peptides (semaglutide, tirzepatide, liraglutide) have completed Phase 3 clinical trials with thousands of human participants. Their safety profiles are well-characterized, side effects are documented, and drug interactions are studied.

Clinically studied peptides (thymosin alpha-1, some GH secretagogues) have human clinical data, often from smaller trials or from approval in other countries. Evidence is meaningful but less comprehensive.

Preclinically studied peptides (BPC-157, TB-500, epitalon, MOTS-c) have animal study data only. Dosing is extrapolated, human safety is not formally characterized, and long-term effects are unknown. This is where most research peptides fall.

Understanding where a peptide sits on this spectrum is essential for making informed decisions.

Universal Safety Principles

Regardless of which peptide you're researching:

Consult a physician. This applies to all peptides, especially those without FDA approval. A knowledgeable provider can monitor biomarkers, flag contraindications, and adjust protocols.
Cancer and angiogenesis. Many healing peptides promote new blood vessel formation (angiogenesis). This is beneficial for recovery but raises theoretical concerns for anyone with active cancer or cancer history, as tumors require blood supply to grow.
Pregnancy and breastfeeding. No research peptide has been studied for safety during pregnancy. Avoid entirely.
Quality matters. For non-FDA-approved peptides, there is no standardized manufacturing quality requirement. Products vary in purity, potency, and sterility. Third-party certificates of analysis from independent labs are the minimum standard.
Start low, go slow. When exploring any new peptide, begin at the lower end of reported dosage ranges and assess tolerance before increasing.
Cycling. Most peptide protocols involve periods of use followed by breaks. Continuous, indefinite use of research peptides is poorly studied and generally not recommended.

Regulatory Status

Peptide regulation varies widely:

FDA-approved (semaglutide, tirzepatide, liraglutide, gonadorelin, ACTH) — available by prescription, regulated manufacturing
Category 2 / restricted (BPC-157, many research peptides) — cannot be legally compounded by US pharmacies
Approved in other countries (thymosin alpha-1, semax, selank) — approved in some markets but not the US
Research-only — most peptides discussed in biohacking communities are officially "for research purposes only"

For more on the regulatory landscape, read our analysis: FDA Peptide Ban: What 75,000 Patients Reveal About Safety.

Getting Started: Practical Next Steps

If you're new to peptides, here's a rational path forward.

Step 1: Identify Your Goal

Are you interested in peptides for healing an injury? Weight management? Anti-aging? Cognitive enhancement? Immune support? Your goal determines which peptides are relevant and what evidence level you should expect.

Step 2: Research the Specific Peptide

Use our Peptide Directory to explore detailed profiles for each peptide — including mechanism of action, research data, safety information, and regulatory status. Don't rely on forum posts or social media claims.

Step 3: Understand the Evidence Level

Know whether you're looking at FDA-approved therapeutics or research compounds with preclinical data only. Both have their place, but the risk-benefit calculation is different.

Step 4: Talk to a Healthcare Provider

Find a physician experienced with peptide therapy. This is especially important for non-FDA-approved compounds, where monitoring via blood work and health assessments adds an essential safety layer.

Step 5: Use Practical Tools

Peptide Dosage Calculator — get exact reconstitution math and syringe draw volumes
Reconstitution Guide — step-by-step instructions for preparing injectable peptides
Peptide Stacks Guide — popular combinations and protocols
Dosage Guides — peptide-specific dosing protocols

Key Takeaways

Peptides are short chains of amino acids that act as signaling molecules — your body already produces and uses them
Therapeutic peptides work by mimicking or enhancing natural biological pathways
The peptide landscape spans FDA-approved medications (semaglutide) to research-only compounds (BPC-157) — evidence levels vary dramatically
Healing, weight loss, growth hormone, anti-aging, cognitive, and immune peptides are the major categories
Safety requires understanding evidence levels, working with a physician, and ensuring product quality
Most research peptides have extensive preclinical data but limited or no human clinical trial data

The peptide space is evolving rapidly, with new clinical trials, regulatory changes, and research emerging regularly. Bookmark our Peptide Directory and Blog to stay current.

This article is for educational and informational purposes only. It is not medical advice. Always consult with a qualified healthcare provider before starting any peptide therapy. See our Medical Disclaimer for more information.