What Are Peptides? The Complete UK Research Guide

If you've been reading about health, fitness, or anti-ageing research in the last few years, you've almost certainly come across the word "peptides." It's everywhere now. On forums, in podcasts, across social media. But what actually are peptides, and why has the research community become so interested in them?

This guide breaks it all down. Whether your completely new to peptide research or you've already been looking into specific compounds, we're going to cover everything from basic definitions to safety profiles, side effects, and how different peptides compare to other compounds on the market.

No jargon overload. No unnecessary fluff. Just a straightforward, honest look at what peptides are and what the current research says about them.

Peptides Explained Simply

At the most basic level, a peptide is a short chain of amino acids. Amino acids are the building blocks of life — there are 20 of them that the human body uses, and they link together in different combinations to form peptides and proteins.

Here's the key distinction: peptides are short chains, typically between 2 and 50 amino acids long. Proteins are longer chains, usually 50 amino acids or more. That's really the main difference. A good way to think about it is this — if proteins are full sentences, then peptides are individual words. Shorter, more targeted, more specific in what they do.

Your body already produces hundreds of peptides naturally. You've heard of some of them, even if you didn't realise they were peptides:

• Insulin — the hormone that regulates blood sugar. It's a peptide of 51 amino acids.
• Oxytocin — sometimes called the "bonding hormone." Just 9 amino acids.
• Endorphins — your body's natural painkillers. These are peptides too.
• Glutathione — a powerful antioxidant made of only 3 amino acids.
• Collagen peptides — the ones you see in skincare products and supplements.

So peptides aren't some alien substance. Their a fundamental part of human biology. Your body makes them, uses them, and depends on them every single day.

Why Do Peptides Matter?

Peptides act as signalling molecules. Think of them like tiny messengers that tell your cells what to do. One peptide might tell your pituitary gland to release growth hormone. Another might signal your immune system to reduce inflammation. A different one might trigger tissue repair at a wound site.

Because peptides are so specific in their signalling, they've attracted enormous interest from researchers. Unlike broad-spectrum drugs that affect multiple systems at once (often causing a wide range of side effects), peptides tend to target particular receptors and pathways. This specificity is what makes them so appealing for research.

Synthetic Peptides

Synthetic peptides are man-made versions of natural peptides, or entirely new sequences designed in a lab to target specific biological pathways. The technology to synthesise peptides has been around since the 1960s, when Robert Bruce Merrifield developed solid-phase peptide synthesis — work that earned him a Nobel Prize in 1984.

Since then, peptide synthesis has become faster, cheaper, and more accessible. Today, there are thousands of synthetic peptides being studied for everything from wound healing to metabolic disorders to cognitive function. The global peptide therapeutics market was valued at over $40 billion in 2023, and it's growing rapidly.

Some synthetic peptides mimic what the body already produces. Others are modified versions designed to last longer or work more effectively. And some are entirely novel sequences that don't exist in nature at all.

How Do Peptides Work?

The basic mechanism is receptor binding. Peptides attach to specific receptors on the surface of cells — like a key fitting into a lock. When the peptide binds to its receptor, it triggers a cascade of signals inside the cell. This cascade can activate genes, produce other proteins, change cellular behaviour, or initiate repair processes.

What makes peptides different from many pharmaceutical drugs is their specificity. A traditional painkiller, for example, might work by broadly suppressing inflammation throughout the entire body. A peptide, on the other hand, might target one specific receptor in one specific tissue type. This is why peptide research has generated so much excitment — the potential for targeted effects with fewer off-target consequences.

That said, peptides aren't magic. They still interact with complex biological systems, and the research is still ongoing for many compounds. But the mechanism of action — targeted receptor binding followed by specific signal cascades — is well established.

Categories of Research Peptides

Research peptides generally fall into several broad categories based on what they target. Here's a breakdown of the main ones:

Growth Hormone Secretagogues

These peptides stimulate the body's own production of growth hormone (GH) rather than introducing external GH directly. They work by acting on the pituitary gland or the hypothalamus.

• CJC-1295 — a modified version of growth hormone-releasing hormone (GHRH). Often studied in combination with other secretagogues. Research focuses on its effects on GH pulsatility and IGF-1 levels.
• Ipamorelin — a selective growth hormone secretagogue that mimics ghrelin. It's considered one of the "cleaner" GH secretagogues because it doesn't significantly raise cortisol or prolactin in research models.
• Sermorelin — one of the earliest GH-releasing peptides studied. It's actually an FDA-approved peptide (in the US) for diagnosing growth hormone deficiency, which tells you something about its established safety profile.

GLP-1 Receptor Agonists

This category has absolutely exploded in popularity. GLP-1 (glucagon-like peptide-1) is a natural hormone involved in blood sugar regulation and appetite. Synthetic versions have become some of the most-researched compounds in modern medicine.

• Semaglutide — the active ingredient in Ozempic and Wegovy. Originally developed for type 2 diabetes, it's now widely studied for weight management and cardiovascular health. Arguably the most well-known peptide in the world right now.
• Tirzepatide — a dual GIP/GLP-1 receptor agonist (brand name Mounjaro). It targets two receptors instead of one, and research has shown impressive results for both glycaemic control and weight reduction.
• Retatrutide — a newer triple agonist targeting GLP-1, GIP, and glucagon receptors simultaneously. Still in clinical trials, but early phase 2 data has generated significant interest in the research community.

Tissue Repair Peptides

These peptides are studied for their potential effects on healing, recovery, and tissue regeneration.

• BPC-157 — stands for "Body Protection Compound." It's a partial sequence of a protein found in gastric juice. Research in animal models has looked at tendon healing, gut repair, and anti-inflammatory effects. One of the most popular research peptides in the UK.
• TB-500 — a synthetic version of thymosin beta-4, a naturally occurring peptide involved in cell migration and tissue repair. Studied for wound healing and recovery from soft tissue injuries.
• GHK-Cu — a copper peptide that naturally occurs in human plasma. Research has focused on its effects on skin remodelling, collagen synthesis, and wound healing. Also popular in skincare research.

Neuropeptides

These target the brain and nervous system. They've attracted interest for cognitive enhancement, stress response, and sleep regulation research.

• Semax — originally developed in Russia, it's a synthetic analogue of ACTH (adrenocorticotropic hormone). Researched for its potential nootropic and neuroprotective properties. Actually approved as a medication in Russia and some CIS countries.
• Selank — another Russian-developed peptide, this one based on the naturally occurring immunopeptide tuftsin. Studied for anxiolytic (anti-anxiety) effects and cognitive function.
• DSIP (Delta Sleep-Inducing Peptide) — as the name suggests, its been studied for sleep regulation. It was first isolated in 1977 from the blood of rabbits during induced sleep.

Metabolic Peptides

These compounds are researched for their effects on metabolism, cellular energy, and body composition.

• NAD+ — technically a coenzyme rather than a peptide, but frequently grouped with peptides in research contexts. It's essential for cellular energy production and DNA repair. NAD+ levels decline with age, which is why supplementation research has become a hot topic.
• Glutathione — the body's master antioxidant. A tripeptide (three amino acids) that plays a crucial role in detoxification and oxidative stress management.
• Tesamorelin — an FDA-approved (in the US) growth hormone-releasing factor analogue. Originally approved for reducing excess abdominal fat in HIV patients, but researched more broadly for body composition and metabolic health.

The Most Researched Peptides

Here's a comprehensive overview of the peptides that UK researchers are most interested in right now. We've included search volume data to give you an idea of how much interest each compound is generating.

Let's take a closer look at each one.

BPC-157

BPC-157 is probably the single most popular research peptide in the UK right now, and for good reason. It's a 15-amino-acid peptide derived from a protein found in human gastric juice. The research, mostly in animal models, has been remarkably consistent. Studies have shown accelerated healing of tendons, ligaments, muscles, and even the gut lining. It's also been studied for its effects on the gut-brain axis and its anti-inflammatory properties.

The limitation? Most of the data comes from rodent studies. Human clinical trials are still limited, though the animal data is extensive and the compound has a strong safety profile in those models.

Semaglutide

You almost certainly know this one already. Semaglutide is the peptide behind Ozempic and Wegovy, and its completely transformed the conversation around weight management and metabolic health. It works by mimicking GLP-1, a hormone that reduces appetite and improves insulin sensitivity. The clinical trial data is robust — we're talking large-scale, randomised, placebo-controlled trials published in top medical journals.

Beyond weight loss, ongoing research is looking at semaglutide's effects on cardiovascular disease, kidney disease, and even addiction. It's a genuine blockbuster compound.

Tirzepatide

Tirzepatide takes the GLP-1 concept a step further by also targeting GIP (glucose-dependent insulinotropic polypeptide) receptors. The SURMOUNT clinical trials showed average weight reductions of up to 22.5% of body weight in some groups, which is unprecedented for a pharmaceutical intervention. It's currently approved as Mounjaro for type 2 diabetes and is being studied extensively for obesity treatment.

TB-500

TB-500 is a synthetic fragment of thymosin beta-4, a peptide that's naturally present in almost all human and animal cells. It's been researched primarily for tissue repair — specifically, how it promotes cell migration to injury sites and supports the formation of new blood vessels (angiogenesis). Animal studies have examined its effects on heart tissue repair, skin wounds, and musculoskeletal injuries.

Researchers often study TB-500 alongside BPC-157, as the two compounds appear to work through complementary mechanisms.

Retatrutide

Retatrutide is the newest and most talked-about weight management peptide. It's a triple agonist — hitting GLP-1, GIP, and glucagon receptors simultaneously. Phase 2 trial results published in the New England Journal of Medicine showed weight reductions of up to 24% over 48 weeks. Phase 3 trials are ongoing, and the research community is watching closely. If the results hold up, it could become the most effective weight management compound ever developed.

GHK-Cu

GHK-Cu (glycyl-L-histidyl-L-lysine copper) is a naturally occurring copper peptide first identified in human plasma in 1973. What makes it interesting is its broad range of studied effects. Research has looked at wound healing, skin remodelling, collagen and elastin production, anti-inflammatory activity, and even hair growth. It's also one of the few peptides thats crossed over significantly into the cosmetics industry — you'll find GHK-Cu in high-end skincare products.

Semax

Semax is a synthetic peptide based on a fragment of ACTH (amino acids 4-10), developed at the Institute of Molecular Genetics in Moscow. It's been approved in Russia as a prescription medication for stroke recovery and cognitive disorders. Research has examined its potential nootropic effects, including improvements in memory, attention, and learning in animal models. It's also been studied for neuroprotective properties.

Selank

Selank is closely related to Semax — same Russian research institute, similar era of development. It's based on the immunopeptide tuftsin with an added Pro-Gly-Pro sequence for stability. The primary research interest is in its anxiolytic (anti-anxiety) effects, with studies also looking at immune system modulation and cognitive function. Like Semax, it's an approved medication in Russia.

NAD+

NAD+ (nicotinamide adenine dinucleotide) is essential for life. Every cell in your body needs it for energy production, DNA repair, and cellular signalling. The problem is that NAD+ levels decline significantly with age — by some estimates, they drop by up to 50% between the ages of 40 and 60. This decline has been linked to many age-related conditions, which is why NAD+ supplementation and precursor research has become such a massive field.

Tesamorelin

Tesamorelin is a synthetic analogue of growth hormone-releasing hormone (GHRH). It's one of the few research peptides that has full FDA approval (in the US) — specifically for the reduction of excess abdominal fat in HIV-infected patients with lipodystrophy. Beyond this specific use case, researchers have studied it for broader body composition effects, cognitive function in ageing, and metabolic health markers.

Are Peptides Safe?

This is the question everyone asks, and it deserves a honest answer.

First, some context. Peptides as a class of molecules are not inherently dangerous. Your body produces and uses peptides constantly. Insulin, one of the most widely used medications on the planet, is a peptide. It's been used clinically since 1922 — over a hundred years. Oxytocin is given routinely during childbirth. GLP-1 agonists like semaglutide have gone through rigorous phase 3 clinical trials involving tens of thousands of participants.

So when someone asks "are peptides safe?", the answer depends entirely on which peptide you're talking about.

Clinically Approved Peptides

Some peptides have extensive human safety data. Semaglutide, tirzepatide, tesamorelin, sermorelin — these have all been through formal clinical trials and regulatory approval processes. Their safety profiles are well documented, their side effects are known, and their risk-benefit ratios have been formally assessed.

Research Peptides

Other peptides — like BPC-157, TB-500, and many others — have less formal human safety data. The research is primarily from animal studies, case reports, and anecdotal evidence from the research community. This doesn't necessarily mean they're dangerous, but it does mean the safety profile is less completely understood compared to FDA-approved compounds.

This is an important distinction that anyone involved in peptide research needs to understand.

How Peptides Differ from Steroids

One common misconception is that peptides are similar to anabolic steroids. They're not. The differences are fundamental:

• No androgenic effects — Peptides don't cause virilisation, hair loss, or the hormonal disruptions associated with androgens.
• No liver toxicity — Unlike oral anabolic steroids (particularly 17-alpha-alkylated compounds), peptides generally don't place significant stress on the liver.
• No HPTA suppression — Most peptides don't suppress the hypothalamic-pituitary-testicular axis the way steroids do. Growth hormone secretagogues, for example, stimulate the body's own GH production rather than replacing it.
• Different mechanism entirely — Steroids work by binding to androgen receptors and directly altering gene expression in muscle cells. Peptides work through targeted receptor signalling, often stimulating the body's own production of hormones or growth factors.

That said, peptides are bioactive compounds and should be treated with appropriate respect. They're not supplements. They're not vitamins. They are compounds that interact with biological systems in specific ways, and the research should be approached accordingly.

Peptide Side Effects

Every bioactive compound has the potential for side effects. Here's what the current research tells us about the most common ones, organised by category.

The Most Common Effects Overall

Across all categories, the most frequently reported side effects in research are:

• Injection site reactions (redness, swelling, mild pain)
• Nausea (especially with GLP-1 agonists, particularly at higher doses)
• Headaches (typically in the first few days of research protocols)
• Water retention (mainly with GH secretagogues)
• Fatigue or changes in energy levels

Most of these effects are dose-dependent, meaning they're more likely at higher doses, and transient, meaning they tend to resolve as the body adjusts.

Serious but Rare Effects

For GLP-1 agonists specifically, there have been reports of pancreatitis and gallbladder issues, though these are uncommon in clinical trial data. For GH secretagogues, prolonged use at high doses could theoretically affect blood sugar regulation or contribute to joint discomfort due to elevated IGF-1 levels. These are areas where ongoing research is particularly important.

Why Purity Matters

Here's something that doesn't get discussed enough: many reported side effects from research peptides may actually be caused by impurities rather than the peptide itself. Low-quality synthesis can leave behind residual solvents, incomplete peptide chains, or other contaminants. This is why sourcing matters enormously.

When you buy peptides from a reputable UK supplier that provides third-party purity testing (typically HPLC analysis showing 98%+ purity), your dramatically reducing the risk of side effects caused by manufacturing impurities. Cheap peptides from unverified sources are a false economy — especially for research purposes where data quality depends on compound quality.

How to Minimise Side Effects in Research

• Start low — Begin with the lowest effective dose and increase gradually.
• Source quality compounds — Only use peptides with verified purity certificates from reputable UK suppliers.
• Proper storage — Degraded peptides can cause more side effects than properly stored ones. Keep reconstituted peptides refrigerated and use them within the recommended timeframe.
• Proper reconstitution — Use bacteriostatic water, not sterile water, for reconstitution. This prevents bacterial contamination.
• Document everything — Good research requires good records. Track dosing, timing, and any effects observed.

Peptides vs Other Compounds

People often want to know how peptides stack up against other types of compounds. Here's a brief comparison.

Peptides vs SARMs

SARMs (Selective Androgen Receptor Modulators) are non-steroidal compounds that bind to androgen receptors. Despite the "selective" name, they can still suppress natural testosterone production and may carry liver toxicity risks. Peptides work through entirely different mechanisms — they don't bind to androgen receptors at all. The two aren't really comparable in terms of mechanism, but peptides generally have a more favourable side effect profile based on current data.

Peptides vs Anabolic Steroids

We covered this above, but to summarise: steroids directly introduce exogenous hormones and cause significant endocrine disruption. Peptides, particularly secretagogues, work with the body's own systems rather than overriding them. Steroids are well-studied but carry well-documented risks including liver damage, cardiovascular strain, hormonal imbalances, and psychological effects. Peptides generally don't carry these same risks, though they have there own considerations.

Peptides vs Nootropics

There's actually some overlap here. Neuropeptides like Semax and Selank are effectively nootropic peptides. Compared to traditional nootropics (racetams, modafinil, caffeine-based stacks), neuropeptides tend to work through more specific receptor mechanisms. Traditional nootropics often modulate broad neurotransmitter systems, while neuropeptides target specific signalling pathways.

Peptides vs Supplements

Supplements (vitamins, minerals, herbal extracts) work through nutritional pathways — they provide something the body needs or can use. Peptides are different. They're signalling molecules that actively instruct cells to do specific things. The effects are generally more pronounced and more targeted than supplements, but they also require more careful handling, proper storage, and more thorough research understanding.

It's not really an either/or situation though. Many researchers use supplements alongside peptide research as part of a comprehensive approach.

How to Get Started with Peptide Research

If your new to peptide research, here's a practical step-by-step approach.

Step 1: Research Your Area of Interest

Don't just pick a peptide because someone on Reddit said it was good. Start by identifying what area of research interests you. Tissue repair? Metabolic health? Cognitive function? Anti-ageing? Each area has specific peptides that are most relevant, and understanding the research behind them before purchasing anything is essential.

Read the published studies. PubMed is free and has abstracts for virtually every relevant paper. Look at what was studied, in what model (animal vs human), at what doses, and what the outcomes were. This gives you a much better foundation than forum posts or social media claims.

Step 2: Source Quality UK Peptides

This is where many people go wrong. The peptide market has grown rapidly, and not all suppliers are equal. Here's what to look for when you buy peptides UK:

• Third-party testing — HPLC (High-Performance Liquid Chromatography) and mass spectrometry results should be available for every batch. Look for purity of 98% or higher.
• UK-based supplier — Faster shipping, no customs complications, and subject to UK business regulations.
• Proper packaging — Peptides should come lyophilised (freeze-dried) in sealed vials, stored and shipped appropriately.
• Transparent information — Good suppliers provide clear information about their products, including molecular weight, sequence, and storage instructions.
• Customer support — A supplier that can answer technical questions about their products is generally a better bet than one that can't.

The best peptides UK researchers can access come from suppliers who prioritise quality over cutting corners on price. It's worth paying a bit more for verified purity.

Step 3: Learn Reconstitution and Storage

Most research peptides come as a lyophilised (freeze-dried) powder that needs to be reconstituted before use. This isn't complicated, but it does need to be done correctly:

• Use bacteriostatic water (not regular sterile water) for reconstitution. The benzyl alcohol in bacteriostatic water prevents bacterial growth, giving the reconstituted peptide a longer usable life.
• Add the water slowly down the side of the vial. Don't inject it directly onto the powder — this can damage the peptide.
• Swirl gently to mix. Never shake vigorously.
• Store reconstituted peptides in the fridge (2-8°C). Most reconstituted peptides are stable for 2-4 weeks when refrigerated properly.
• Unreconstituted (lyophilised) peptides should be stored in the freezer for long-term storage.

Step 4: Understand the Legal Framework

In the UK, peptides occupy an interesting legal space. They are legal to buy and possess for research purposes. They are not controlled substances under the Misuse of Drugs Act. However, they are not licensed for human consumption — they are sold strictly as research chemicals.

This is an important distinction. Peptides sold for research purposes are not medicines, they are not supplements, and they are not food products. They are chemical compounds intended for in vitro and laboratory research. All reputable UK peptide suppliers operate within this legal framework.

It's also worth noting that some peptides (particularly semaglutide and tirzepatide) are available as prescription medications through the NHS or private clinics. The prescription versions are manufactured to pharmaceutical-grade standards and come with full regulatory approval. Research-grade versions are a different product category entirely.

Peptide Therapy: What Is It?

You might have seen the term "peptide therapy" used online, particularly on American websites and clinics. Peptide therapy refers to the clinical use of peptides, prescribed and monitored by a healthcare professional, to address specific health conditions or optimise biological function.

In the US, peptide therapy clinics have become increasingly common, offering protocols involving various peptides for anti-ageing, weight management, recovery, and more. In the UK, things are quite different. While some private clinics do offer peptide-based treatments (particularly semaglutide for weight management), the concept of dedicated "peptide therapy clinics" is less established.

It's important to distinguish between peptide therapy (clinical, supervised) and peptide research (laboratory, academic). Our products are sold for research purposes, not for peptide therapy or self-administration.

Frequently Asked Questions

What are peptides used for?

In a research context, peptides are used to study a wide range of biological processes. Different peptides are researched for different purposes — BPC-157 and TB-500 for tissue repair mechanisms, semaglutide and tirzepatide for metabolic pathways, Semax and Selank for neurological function, and GHK-Cu for skin biology and wound healing. Clinically, peptides like insulin, semaglutide, and oxytocin are used as approved medications for specific conditions.

Are peptides steroids?

No. Peptides and steroids are completely different types of molecules. Peptides are chains of amino acids. Steroids are a class of organic compounds with a specific four-ring molecular structure. They work through entirely different mechanisms. Peptides signal through cell-surface receptors; steroids typically cross the cell membrane and bind to intracellular receptors. The side effect profiles are also very different — peptides don't cause the androgenic, hepatotoxic, or endocrine-disrupting effects associated with anabolic steroids.

Do peptides have side effects?

Yes, like any bioactive compound, peptides can have side effects. The most common are injection site reactions, nausea (particularly with GLP-1 agonists), headaches, and water retention (with GH secretagogues). Most side effects are mild, dose-dependent, and transient. Serious side effects are rare, particularly with properly sourced, high-purity compounds used at appropriate research doses. See the detailed side effects section above for a category-by-category breakdown.

Are peptides legal in the UK?

Yes. Peptides are legal to purchase and possess in the UK for research purposes. They are not controlled substances under the Misuse of Drugs Act 1971 or the Psychoactive Substances Act 2016. They are sold as research chemicals, not as medicines, supplements, or food products. Some peptides (like semaglutide) are also available as prescription medications through licensed healthcare providers, but the research-grade and pharmaceutical-grade products are distinct categories.

What is the best peptide for beginners?

There's no single "best" peptide — it depends entirely on your research interest. That said, BPC-157 is often considered a good starting point for researchers new to peptides because it has a large body of animal research behind it, a relatively well-understood mechanism of action, and a favourable safety profile in studies. For those interested in neuropeptide research, Semax is another commonly recommended starting point due to its established use in Russian clinical settings.

How do you take peptides?

Research peptides are typically administered via subcutaneous injection (under the skin) after reconstitution with bacteriostatic water. Some peptides, like Semax and Selank, are available in intranasal form. A few, like oral BPC-157, are being studied in oral formulations, though injection remains the standard route for most research peptides due to better bioavailability. Proper reconstitution, sterile technique, and correct storage are all essential for maintaining compound integrity.

What is a peptide in simple terms?

A peptide is a small chain of amino acids — typically between 2 and 50 amino acids linked together. Think of amino acids as individual letters, peptides as words, and proteins as full sentences. Your body makes hundreds of natural peptides that act as chemical messengers, telling your cells what to do. Synthetic peptides are lab-made versions designed to study or mimic these natural processes.

How long do peptides take to work?

This varies massively depending on the peptide and the research endpoint being measured. GLP-1 agonists like semaglutide typically show measurable effects on appetite within days, with significant weight changes over weeks to months. GH secretagogues may take several weeks to produce measurable changes in IGF-1 levels. Tissue repair peptides like BPC-157 have shown effects in animal studies within days to weeks depending on the injury model. Neuropeptides like Semax may show acute effects within hours.

All products are sold for research purposes only. These products are not intended for human consumption. Always consult published research literature and follow appropriate laboratory protocols when conducting peptide research.

Looking for high-purity research peptides with third-party testing? Browse our full range of UK peptides, including BPC-157, semaglutide, tirzepatide, and more. Every batch is tested for purity and shipped from within the UK for fast, reliable delivery.