Peptides Explained: What They Do and What the Research Says

What are peptides?

Peptides are short chains of amino acids that act as signalling molecules in the body. Some occur naturally; others are synthetic versions or modified analogues designed to influence a particular biological pathway.
The reason the subject can become confusing is that the word peptide covers a huge range of compounds. A peptide discussed for tendon recovery may have almost nothing in common with one being researched for skin, metabolism or growth-hormone signalling.
This guide focuses on the names that are now appearing most often outside the weight-loss medicines already covered elsewhere on The Peptide Brief. Each section explains the intended or proposed effect first, then puts the strength of the evidence into context.

The main peptides explained

Use this as a quick directory, then scroll down for a plain-English explanation of what each peptide is intended or researched to do.

BPC-157 — tissue repair, tendons and gut research

BPC-157 is mainly talked about as a recovery peptide, particularly for tendon, ligament and muscle injuries. It also comes up frequently in discussions around gut health and inflammation.
The interest comes largely from laboratory and animal studies, where researchers have looked at its possible role in tissue repair, healing and inflammation. The big catch is that research in people is still extremely limited. A 2026 review found fewer than 30 people across three small, uncontrolled pilot studies, with no completed Phase II clinical trial. So while BPC-157 is an interesting area of research, we simply don’t yet have good clinical evidence showing that it works in people in the way it’s often described online.

Read our full BPC-157 UK guide →

TB-500 — recovery and soft-tissue repair

TB-500 is mainly talked about as a recovery peptide, particularly for muscle, tendon and other soft-tissue injuries. It’s often mentioned alongside BPC-157 because both are associated with healing and recovery, although they are different peptides and work in different ways.
TB-500 is related to thymosin beta-4, a naturally occurring peptide involved in processes such as cell movement and tissue repair. There has been human research into thymosin beta-4 itself, but that doesn’t prove that TB-500 has the same effects. Research specifically supporting TB-500 in people is still limited, so claims around faster healing or injury recovery currently go further than the clinical evidence.

Read our full TB-500 UK guide →

GHK-Cu — copper peptide for skin, collagen and hair

GHK-Cu is mainly talked about as a skin and hair peptide. It’s a naturally occurring peptide that binds to copper and has attracted attention for its possible role in collagen production, skin repair, elasticity and hair growth.
That’s why you’ll now see GHK-Cu appearing in everything from anti-ageing skincare to discussions about thinning hair and loose or ageing skin. There is genuine research behind GHK-Cu and how it interacts with skin and tissue, but the evidence for some of the bigger cosmetic claims isn’t as strong as the marketing can make it sound. A 2025 review, for example, found that good-quality clinical evidence for topical GHK-Cu is still fairly limited.

Read our full GHK-Cu UK guide →

MOTS-C — metabolism, mitochondria and exercise

MOTS-C is mainly talked about for energy, metabolism, exercise and healthy ageing. It’s a little different from many other peptides because it is naturally produced from our mitochondrial DNA — the part of our cells involved in producing energy.
Researchers are interested in MOTS-C because it appears to play a role in how the body uses energy and responds to exercise. Human studies have shown that our own MOTS-C levels can change with exercise, while animal studies have suggested possible benefits for physical performance and metabolic health. What we don’t yet know is whether using synthetic MOTS-C in people produces those same benefits. So it’s an exciting area of research, but many of the claims you’ll see around energy, fitness and anti-ageing are still ahead of the human evidence.

CJC-1295 — growth hormone and IGF-1 signalling

CJC-1295 is mainly talked about for recovery, muscle growth and body composition. Rather than supplying growth hormone directly, it is designed to encourage the body to release more of its own growth hormone, which can also increase levels of IGF-1.
There is human research showing that CJC-1295 can raise growth hormone and IGF-1 levels. Where things become less certain is whether that automatically leads to all the benefits often associated with it, such as more muscle, less body fat, faster recovery or anti-ageing effects. You may also see CJC-1295 with DAC and “CJC-1295 no DAC” mentioned online. They shouldn’t simply be treated as the same thing, as the DAC version was specifically designed to stay active in the body for much longer.

Read our full CJC-1295 UK guide →

Ipamorelin — stimulating growth-hormone release

Ipamorelin is mainly talked about for recovery, sleep, muscle growth and body composition. It works by encouraging the body to release more of its own growth hormone, rather than supplying growth hormone directly.
Human studies have shown that Ipamorelin can trigger a rise in growth hormone, which is why it has attracted so much interest. It is also commonly mentioned alongside CJC-1295, as the two encourage growth-hormone release in different ways. The important distinction is that showing an increase in growth hormone doesn’t automatically prove claims around better sleep, faster recovery, increased muscle or fat loss. Those longer-term benefits have much less clinical evidence behind them.

KPV — inflammation, gut and skin research

KPV is mainly talked about for inflammation, gut health and skin problems. It’s a very small peptide derived from a naturally occurring hormone and has attracted attention because of its possible anti-inflammatory effects.
Most of the research so far has been in laboratory and animal studies, particularly looking at inflammation involving the gut and skin. That’s why KPV often appears alongside peptides such as BPC-157 in discussions around gut health, intestinal inflammation and tissue repair. The important catch is that human evidence is still very limited, so KPV hasn’t been proven as a treatment for conditions such as inflammatory bowel disease or dermatitis.

Tesamorelin — growth-hormone signalling and visceral fat

Tesamorelin is mainly talked about for reducing visceral fat — the deeper abdominal fat that sits around the internal organs. It works by encouraging the body to release more of its own growth hormone, which in turn increases IGF-1.
Tesamorelin is a little different from many of the peptides on this page because it has been properly studied in people and has an approved medical use in the United States for reducing excess abdominal fat in adults with HIV-associated lipodystrophy. That has understandably led to wider interest in it for fat loss and body composition, but there’s an important distinction: evidence that it works for this specific medical condition doesn’t mean it has been proven as a general weight-loss or fat-loss peptide.

Selank — stress, anxiety and cognition

Selank is mainly talked about for anxiety, stress and mental focus. It sits at a very different end of the peptide world from the recovery and body-composition peptides, and is usually described as a nootropic — something being researched for possible effects on the brain and cognitive performance.
Research has looked at whether Selank could influence anxiety, stress responses, memory and concentration, but much of that work has come from Russia and the wider international evidence is still fairly limited. So while you may see Selank described as a peptide for calmness, focus or anxiety, the research isn’t strong enough to treat those benefits as proven.

Semax — cognition and neuroprotection

Semax is mainly talked about for focus, memory and brain health. Like Selank, it sits in the nootropic side of the peptide world and has been researched for possible effects on cognitive function and protecting the brain.
Some of the research into Semax has involved people recovering from stroke and brain injury, while it is now increasingly discussed more broadly for concentration, memory and mental performance. Much of the published research comes from Russia and Eastern Europe, and there is far less evidence showing benefits in otherwise healthy people. So while Semax has some interesting research behind it, the idea of it as a proven “brain booster” goes further than the evidence currently supports.

Epitalon — ageing, sleep and longevity research

Epitalon, also known as Epithalon, is mainly talked about for healthy ageing, longevity and sleep. It has attracted particular attention because researchers have looked at whether it could influence melatonin, the body’s sleep-wake cycle, and processes involved in how our cells age.
You’ll also see Epitalon mentioned alongside telomeres — the protective ends of our chromosomes that naturally shorten as cells age. This has led to some big claims around slowing ageing and even extending lifespan. There is some interesting laboratory and small-scale human research behind Epitalon, but we don’t have strong modern clinical evidence showing that it can reverse ageing or make people live longer. For now, the longevity claims are considerably bigger than the evidence.

IGF-1 LR3 — muscle-growth and recovery signalling

IGF-1 LR3 is mainly talked about for muscle growth, recovery and physical performance, particularly in bodybuilding circles. It is a modified, longer-lasting version of IGF-1, a naturally occurring growth factor that plays an important role in the growth and repair of muscle, bone and other tissues.
That connection with muscle growth explains the interest, but IGF-1 affects far more than just muscle, so it isn’t as simple as a “muscle-building peptide”. There is established medical research around IGF-1 itself, but that shouldn’t be confused with good clinical evidence for IGF-1 LR3 products sold online. Claims around increased muscle, faster recovery and improved performance therefore need to be treated with caution.

Melanotan II — the tanning peptide

Melanotan II is mainly known as the “tanning peptide”. It works by increasing the production of melanin — the pigment that gives skin its colour — which is why it is associated with tanning without needing as much sun exposure.
You’ll see Melanotan II sold in injectable form and in products marketed as tanning nasal sprays. Although its effect on pigmentation is well recognised, that doesn’t mean products bought online have been proven safe. Melanotan II can affect more than just skin colour, and reported effects include nausea, facial flushing, changes in appetite and sexual effects. So while the tanning effect explains its popularity, it shouldn’t be mistaken for an ordinary cosmetic tanning product.

Common peptide combinations explained

A few names repeatedly appear together, which can make them look like single products when they are actually separate compounds. BPC-157 + TB-500 is usually grouped around tissue-repair and recovery research. BPC-157 + KPV appears most often in gut and inflammation discussions. CJC-1295 + Ipamorelin combines two different ways of stimulating the growth-hormone axis. The fact that two peptides are commonly paired does not establish that the combination has been clinically tested or shown to work better than either compound alone. On The Peptide Brief we will treat combinations as separate research questions rather than assuming that a popular ‘stack’ has supporting clinical evidence.

Frequently Asked Questions

Sources and editorial methodology

Page last reviewed: 23 August 2026. This guide was compiled by The Peptide Brief editorial team. We use peer-reviewed human research where available and clearly distinguish it from animal, laboratory and mechanistic evidence. Online communities may help us identify the questions people are searching for, but community claims are not used as evidence.
Key research used for this page:
BPC-157: Mateescu DM et al. Pharmaceutics, 2026 — review of translational development and human evidence.
GHK-Cu: Pickart L et al. BioMed Research International, 2015, plus a 2025 review of topical GHK and anti-wrinkle evidence.
CJC-1295: Teichman SL et al. Journal of Clinical Endocrinology & Metabolism, 2006 — randomized human pharmacology studies of GH and IGF-1 responses.
Ipamorelin: Gobburu JV et al. Pharmaceutical Research, 1999 — human pharmacokinetic/pharmacodynamic study.
MOTS-C: Reynolds JC et al. Nature Communications, 2021 — exercise-induced MOTS-C and metabolic adaptation research.
Thymosin beta-4: randomized controlled human safety study published in 2010; TB-500 is discussed separately because it is a thymosin beta-4 fragment rather than the full peptide.
We do not publish dosing protocols or treat seller claims, forum posts or anecdotal reports as clinical evidence.
Spotted something out of date or incorrect? Email corrections@thepeptidebrief.co.uk and we will investigate.

This guide is for information and research purposes only and does not constitute medical advice. Do not start, stop or change any treatment based on information on this page.