What Are Peptides? A Complete Beginner's Guide

Peptides are short chains of amino acids, the same building blocks that make up protein, usually up to around 50 of them. Most act as signalling molecules: they bind a specific receptor to relay a message the body already understands, rather than forcing a reaction the way a drug does. Almost all are sold as research compounds in freeze-dried powder form.

If you have landed here, you have probably seen the names thrown around: BPC-157, retatrutide, GHK-Cu. They get talked about like a single category of miracle compound, and they are not. Peptides are a broad family, they do very different jobs, and some of the noise around them is overblown while some of the genuinely interesting stuff gets buried.

This is the plain-English version. What peptides actually are, how they differ from drugs and hormones, why they show up as a freeze-dried powder, the main categories with real examples, how they are used at a high level, and the honest reality of buying research compounds. No hype, no fearmongering, just what you need to know before you start.

What exactly is a peptide?

A peptide is a short chain of amino acids held together by peptide bonds, the same amino-acid building blocks that make up protein, just far fewer of them. The usual rule of thumb: up to around 50 amino acids and you call it a peptide; beyond that it is a protein. Your body runs on proteins, and amino acids are the Lego bricks that build them.

That small size is the whole point. A peptide is short enough to be made in a lab cheaply and precisely, but long enough to carry a specific message. Many of the peptides people use are copies, or close fragments, of signalling molecules the body already produces. GHK-Cu is a copper-binding peptide found naturally in human plasma. BPC-157 is derived from a protective protein in stomach acid. MOTS-c is a signal your own mitochondria put out. You are not introducing something completely alien; in a lot of cases you are topping up or mimicking a signal that is already part of your biology.

Peptides vs drugs vs hormones: what's the difference?

A signalling peptide differs from a classic drug by binding a specific receptor to relay a message the body already understands, where a small-molecule drug is usually a foreign chemical engineered to block or force a reaction. Some peptides are hormones, or fragments of them, while others are signals that prompt the body to release its own hormone. This is where beginners get tripped up, so it is worth being precise.

Versus most drugs: a classic small-molecule drug is a foreign chemical designed to block, bind, or force a reaction, often hitting more than one target and dragging side effects along with it. A signalling peptide is more like a key cut for one lock. It binds a specific receptor in lab and animal models, which tends to make peptides more targeted, though "targeted" is not the same as "harmless".

Versus hormones: some peptides are hormones, or fragments of them. The GLP-1 compounds like retatrutide and tirzepatide are designed to mimic gut hormones the body releases after a meal. Growth hormone secretagogues (compounds that prompt the body to release its own hormone) like CJC-1295 and ipamorelin act on the pituitary to release endogenous growth hormone, rather than supplying growth hormone itself. The distinction matters in the research: a secretagogue is intended to work with the natural pulsatile rhythm, where supplying the finished hormone overrides it.

The takeaway for a beginner: peptides are generally precise signals, but precise does not mean trivial. The strong ones act on real physiology, and they deserve respect.

Why do peptides come as a powder?

Peptides come as a powder because they degrade in liquid, so they are freeze-dried (the technical word is lyophilised) into a stable, shelf-friendly state. Open your first vial and you will find a tiny white pellet, sometimes called a "puck" or a "cake", sitting at the bottom. That is the peptide. Left in liquid at room temperature, those amino-acid chains start breaking down and lose their activity, so freeze-drying pulls the water out to preserve them.

The visible puck is usually bulked out with a small amount of an excipient (an inactive bulking ingredient) like mannitol that helps it hold its shape and stability.

Before use you reconstitute it: reconstitution means mixing the dry powder with liquid to make it injectable, so you add bacteriostatic water to the vial, let it dissolve, and you have your usable solution. Bacteriostatic water (BAC water) is the correct choice because it contains a small amount of benzyl alcohol that keeps bacteria from growing, so a multi-dose vial stays usable for weeks in the fridge. Primogen supplies BAC water for exactly this reason.

The water volume sets your concentration, and the maths is just division. A 5 mg vial reconstituted with 2 mL of BAC water gives 2.5 mg/mL, so drawing to the 10-unit mark on a standard 100-unit (1 mL) insulin syringe pulls 0.1 mL, which is 250 mcg. Add 5 mL to the same vial instead and that 10-unit mark holds 100 mcg. The peptide quantity never changes; only the dilution does. The full step-by-step, including how much water to add and how to store the result, is in how to reconstitute and store.

What are the main types of peptides?

The main types of peptides group by what they are studied for: healing and recovery, weight-loss GLP-1 agonists, growth hormone secretagogues, cosmetic skin and hair peptides, and a long tail of immune and metabolic compounds. Peptides are best understood by these families, so here they are with examples from the range Primogen actually stocks.

What are healing and recovery peptides?

Healing and recovery peptides are the family studied for tissue repair in tendons, ligaments, muscle and gut lining, and they are the flagship category most beginners start with. BPC-157 and TB-500 are the two best known.

• BPC-157 is a synthetic peptide derived from a protein in stomach acid. In animal models it has been studied for tendon, ligament, muscle and gut-tissue repair, with proposed mechanisms involving angiogenesis (the growth of new blood supply to damaged tissue) and a shift toward the anti-inflammatory healing phase (Sikiric et al., Frontiers in Pharmacology 2021). It remains a research compound: the strongest evidence is preclinical (overwhelmingly animal studies), with only limited early-stage human research to date, and it is worth saying so plainly.
• TB-500 is a synthetic fragment of Thymosin Beta-4 studied in animal models for cell migration to injury sites and modulation of inflammation. It is often run alongside BPC-157 in research protocols because the two are seen as complementary.

These two are frequently paired, and we lay out exactly how they compare in the healing peptides compared.

What are GLP-1 weight-loss peptides?

GLP-1 weight-loss peptides are the family designed to mimic gut hormones that regulate appetite and metabolic control, and they are the category that put peptides on the map for the general public. Retatrutide and tirzepatide are the two Primogen stocks.

• Retatrutide is a triple agonist (a compound designed to switch on three receptors), targeting GLP-1, GIP and glucagon receptors at once. In its pharmacology the glucagon arm is what sets it apart, adding an energy-expenditure pathway on top of the appetite-signalling of GLP-1 (Coskun et al., Cell Metabolism 2022). In a Phase 2 trial, participants on the 12 mg dose lost up to roughly 24% of body weight at 48 weeks (Jastreboff et al., NEJM 2023), and a related analysis reported around an 82% reduction in liver fat (Sanyal et al., Nature Medicine 2024). It is in Phase 3.
• Tirzepatide is the dual agonist (GLP-1 + GIP), FDA-approved, with the longest clinical record of the modern options and the most thoroughly characterised profile.

Primogen stocks both and deliberately does not stock semaglutide, which the newer two outperform in the trial data. The full breakdown is in the GLP-1 comparison.

What are growth hormone secretagogues?

Growth hormone secretagogues are peptides designed to signal the pituitary to release more of the body's own growth hormone, rather than supplying growth hormone itself. CJC-1295, ipamorelin and tesamorelin are the main examples.

• CJC-1295 is a GHRH analogue (a copy of the natural signal that prompts growth-hormone release) intended to drive a larger, sustained release. In one study of healthy adults, single doses produced sustained multi-fold increases in mean GH and IGF-1 (Teichman et al., JCEM 2006).
• Ipamorelin acts on a different receptor (the ghrelin/GHS receptor). In the original pharmacology work it stimulated GH release with greater selectivity than older secretagogues, without the marked ACTH and cortisol response they produced (Raun et al., Eur J Endocrinol 1998). The two are commonly run together in research protocols because the pathways are complementary, a classic example of peptide stacking.
• Tesamorelin is a related GHRH analogue that is FDA-approved for reducing excess visceral abdominal fat in HIV-associated lipodystrophy.

What are cosmetic skin and hair peptides?

Cosmetic skin and hair peptides are the family studied for collagen and skin-matrix signalling, with GHK-Cu the most prominent example. It is one of the most studied cosmetic peptides going.

• GHK-Cu is a naturally occurring copper-binding peptide found in human plasma. In laboratory research it has been studied for collagen-synthesis signalling and skin-matrix remodelling, and a human gene-expression review reported that it modulates the expression of a large share of human genes (Pickart & Margolina, Int J Mol Sci 2018). It is researched both as a topical and as an injectable.

What other peptide categories are there?

Beyond the headline categories there is a long tail of immune, metabolic, nootropic and longevity peptides. Examples include KPV (a fragment studied for anti-inflammatory signalling, used in Primogen's KLOW blend) and MOTS-c (a mitochondrial-derived peptide studied in animal models for exercise-related metabolic pathways). The field is wide, and new compounds appear constantly.

How are peptides used in research?

In research the workflow is the same for most injectable peptides: reconstitute the freeze-dried vial with bacteriostatic water, store the solution cold and dark, and administer a small subcutaneous injection. The high-level steps:

1. Reconstitute. Add bacteriostatic water to the freeze-dried vial and swirl gently (never shake, it can damage the peptide). The amount of water you add sets your concentration and therefore how many units you draw per dose.
2. Store correctly. Reconstituted peptides live in the fridge, away from light, and are not frozen. Most stay good for roughly three to four weeks once mixed, which is why smaller vials are often the smarter buy, you finish them before they degrade.
3. Inject subcutaneously. The standard route for most peptides is a small subcutaneous injection (just under the skin), into the fat just under the skin of the abdomen, using an insulin syringe. Some compounds use other routes (GHK-Cu is also topical, certain nootropic peptides are nasal), but subcutaneous is the default. A few people use intramuscular for specific cases. Intravenous is not something we cover or recommend.

The exact water volumes, dosing maths, and storage detail are all in how to reconstitute and store. Get comfortable with that one page before your first vial and you will avoid almost every beginner mistake.

Are research peptides legitimate and tested?

Research peptides are sold legally as research compounds, not as approved drugs for general human consumption, and across the sector proper per-batch third-party testing is the exception rather than the rule. Here is the part most retailers skip, and it is the part that actually protects you.

These are research compounds. With a few exceptions (tirzepatide and tesamorelin are approved medicines for specific conditions), the peptides in this space are sold for research use, not as approved drugs for general human consumption. That framing is not a marketing dodge, it is the genuine regulatory status, and you should treat it as real.

The manufacturing is mostly Chinese, and per-batch testing is thin. The overwhelming majority of research peptides worldwide come out of Chinese manufacturers. Quality varies, and proper per-batch third-party testing is the exception rather than the rule across the entire sector. We will say this plainly: Primogen has not done its own independent third-party testing of its stock. Where a product line has a supplier reference certificate of analysis (a lab report, called a COA, on a peptide's identity and purity), that is a supplier-level document, not a Primogen test, and it is worth understanding what it does and does not prove. There is a plain-English walkthrough in how to read a COA.

Some data is early. A lot of the most-discussed peptides rest on animal studies and small or preliminary human trials. BPC-157's strongest evidence is preclinical, and the FDA has placed it on its Category 2 list of bulk drug substances flagged for potential safety risks in compounding (FDA, Certain Bulk Drug Substances for Compounding, Sept 2023). Retatrutide's headline Phase 3 numbers are partly topline figures, not fully peer-reviewed papers. That does not make the research worthless, the mechanism and trial signals are often genuinely interesting, but it does mean you should hold the strongest claims a little more loosely than a pharma advert would.

None of this is meant to scare you off. It is meant to set expectations honestly, which is the whole point of the brand.

What are the basic safety and handling rules?

The basic handling rules apply across the board: ramp doses slowly, expect minor injection-site reactions, keep technique sterile, and never store different peptides mixed in one vial. A few ground rules:

• Start low, go slow. Whatever the compound, begin at the low end of the dose range. This is doubly true for the GLP-1 compounds, where ramping the dose too fast is the most commonly reported cause of early gastrointestinal side effects such as nausea.
• Injection-site reactions are common and usually minor. Mild redness or stinging is frequently reported. High-concentration GHK-Cu in particular can sting, which is why it is diluted further. Rotate your injection sites.
• Sterile technique matters. Wipe the vial top, use a fresh needle, do not touch the needle. Most problems beginners report are technique problems, not the peptide.
• Don't mix peptides in one vial for storage. Some combinations (BPC-157 with TB-500 or GHK-Cu, for instance) can degrade each other if stored together. Pre-formulated blends are made to be stable; mixing your own in a vial is not. More on combining them properly in peptide stacking.
• Be realistic about timelines. Research and community reports describe peptide effects building over weeks to months rather than days, so nothing here is overnight.

The risks are real but manageable, and the biggest one for most beginners is simply expecting too much, too fast, from a vial they reconstituted wrong.

Which peptide should a beginner start with?

For most beginners the common on-ramps are the healing peptides (BPC-157, TB-500) or a GLP-1 (tirzepatide, retatrutide), because both are the best-documented categories with well-understood research protocols and a simple practical side once you have reconstitution down. Which fits depends entirely on your research goal.

The honest summary: peptides are precise biological signals, most come as a fragile powder you mix and inject yourself, almost all are research compounds with a mostly-Chinese supply chain and patchy per-batch testing, and the smart beginner respects both the upside and that reality in equal measure.