The Complete Guide to Peptides: What They Are, How They Work & What the Science Says (2026)

⚠️ Medical Disclaimer: This article is for educational purposes only. It is not medical advice. Peptides can have serious side effects and interactions. Always talk to your doctor before using any peptide. Never self-diagnose or self-treat based on internet research.

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Key Takeaways

• Peptides are short chains of amino acids — the same building blocks that make up proteins. Your body already makes hundreds of them naturally.
• They work like keys that fit into specific locks (receptors) on your cells, telling your body to do things like heal, grow, or burn fat.
• Some peptides are FDA-approved medicines (like semaglutide for weight loss). Others are sold as "research chemicals" with limited human data.
• Safety varies wildly depending on the peptide, the source, and how you use it. Some are well-studied. Many are not.
• The peptide market is changing fast — the FDA is cracking down on compounding pharmacies and gray-market vendors in 2026.
• Always consult a healthcare provider before considering any peptide therapy.

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What Are Peptides? A Simple Explanation

Let's start with the basics.

Your body is made of proteins. Proteins are made of amino acids — think of amino acids as tiny LEGO bricks. When you string a few of these bricks together (between 2 and 50), you get a peptide. String together more than 50, and you get a protein.

That's it. A peptide is just a short chain of amino acids.

But don't let the simplicity fool you. Peptides are some of the most powerful signaling molecules in your body. They tell your cells what to do: when to grow, when to heal, when to release hormones, and when to fight infections.

Your body makes over 7,000 known peptides naturally. Insulin (which controls blood sugar) started as a peptide before scientists learned to make it in a lab. So did oxytocin (the "love hormone") and endorphins (your natural painkillers).

How Peptides Differ from Proteins

The main difference is size:

Because peptides are smaller, they can often get into places that larger proteins can't. This makes them useful as drugs — they're big enough to be specific (targeting just one receptor) but small enough to actually reach that receptor.

Natural Peptides Your Body Already Makes

You don't need to take a supplement to benefit from peptides. Your body produces them every day:

• Insulin — Controls your blood sugar levels. Made by your pancreas.
• Endorphins — Natural painkillers. Released during exercise ("runner's high").
• Oxytocin — Bonding and social connection. Released during hugging, breastfeeding.
• GLP-1 — Tells your brain you're full after eating. This is what drugs like Ozempic mimic.
• Growth hormone-releasing hormone (GHRH) — Signals your pituitary gland to release growth hormone.
• BPC (Body Protection Compound) — Found in your stomach juices. Helps protect your gut lining.
• Thymosin beta-4 — Helps with wound healing and tissue repair.

The peptides people buy and use are either copies of these natural peptides or modified versions designed to work better, last longer, or target specific problems.

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How Do Peptides Work in Your Body?

The Lock-and-Key Mechanism

Think of your cells as houses with very specific locks on the doors. Each lock (called a receptor) only opens with the right key. Peptides are those keys.

When a peptide binds to its receptor, it sends a signal inside the cell. That signal triggers a chain reaction — like dominoes falling — that produces a specific effect.

For example:
- Semaglutide (a GLP-1 peptide) fits into GLP-1 receptors in your brain and gut. This makes you feel full and slows down digestion. Result: you eat less and lose weight.
- BPC-157 interacts with several pathways related to blood vessel growth and inflammation. Result: animal studies show faster healing (though human trials are still lacking).
- CJC-1295 binds to growth hormone-releasing hormone receptors. Result: your pituitary gland releases more growth hormone.

Each peptide has its own receptor target. That's what makes them specific — and that's also why different peptides have very different effects.

Why Size Matters: Bioavailability

Here's a problem with peptides: your stomach destroys most of them.

Your digestive system is designed to break down proteins and peptides into individual amino acids. So if you swallow a peptide pill, your stomach acid and enzymes will usually chop it up before it can do anything useful.

This is why most peptides are given by injection (subcutaneous — just under the skin). It's also why oral peptides are so hard to develop.

The notable exception is oral semaglutide (brand name Rybelsus). Scientists solved the bioavailability problem by packaging semaglutide with a special absorption enhancer called SNAC that protects it from stomach acid and helps it pass through the stomach lining. Even so, only about 1% of the oral dose actually makes it into your bloodstream. (According to a 2019 study in Clinical Pharmacokinetics, DOI: 10.1007/s40262-019-00827-4)

Other delivery methods include:
- Nasal sprays — Used for peptides like Semax and Selank (cognitive peptides)
- Topical creams — Used for skin peptides like GHK-Cu
- Sublingual (under the tongue) — Some peptides can absorb through the thin tissue under your tongue

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Types of Peptides by Function

Peptides can be grouped by what they do in the body. Here are the major categories:

Weight Loss Peptides

These are the peptides getting the most attention right now, thanks to drugs like Ozempic and Mounjaro.

How they work: Most weight loss peptides mimic a hormone called GLP-1 (glucagon-like peptide-1). GLP-1 tells your brain you're full, slows stomach emptying, and helps control blood sugar.

Key peptides in this group:
- Semaglutide (Ozempic, Wegovy, Rybelsus) — The blockbuster. FDA-approved for both diabetes and weight loss. Average weight loss of 15-17% body weight in clinical trials. Read our full semaglutide guide →
- Tirzepatide (Mounjaro, Zepbound) — A newer dual-action peptide (GLP-1 + GIP). Clinical trials show even more weight loss than semaglutide — up to 22.5% body weight in some studies.
- Retatrutide — A triple-action peptide (GLP-1 + GIP + glucagon) in late-stage trials. Early data shows up to 24% weight loss.
- AOD-9604 — A fragment of human growth hormone. Some research suggests fat-burning effects, but evidence is weaker than GLP-1 drugs.

Evidence level: Strong for semaglutide and tirzepatide (large clinical trials, FDA-approved). Moderate for retatrutide (Phase 3 trials ongoing). Weak for AOD-9604 (limited human data).

👉 Read our complete guide to weight loss peptides →

Recovery and Healing Peptides

These peptides are popular among athletes and people recovering from injuries.

How they work: They promote blood vessel growth (angiogenesis), reduce inflammation, and support tissue repair through various pathways.

Key peptides in this group:
- BPC-157 (Body Protection Compound-157) — Derived from a protein found in stomach juice. Over 100 animal studies show impressive healing effects on tendons, ligaments, muscles, and the gut. However, there are no published human clinical trials. This is important to understand. Read our BPC-157 guide →
- TB-500 (Thymosin Beta-4) — A naturally occurring peptide involved in wound healing and cell migration. Like BPC-157, most evidence comes from animal studies.
- GHK-Cu (Copper Peptide) — A tripeptide (just 3 amino acids) that binds copper. Research shows effects on skin repair, collagen production, and wound healing. Has more human data than BPC-157, especially for topical use.

Evidence level: Moderate to strong in animal models. Weak in humans (especially BPC-157 and TB-500). GHK-Cu has more human skin research.

👉 Read our complete guide to recovery peptides →

Anti-Aging Peptides

These target the biological mechanisms of aging: telomere shortening, cellular senescence (zombie cells), oxidative damage, and hormone decline.

Key peptides in this group:
- Epithalon (Epitalon) — A synthetic version of a natural peptide called epithalamin. Research by Dr. Vladimir Khavinson suggests it may activate telomerase, the enzyme that maintains telomere length. Most data comes from Russian studies with limited Western replication.
- GHK-Cu — Cross-category champion. Also appears here for its skin rejuvenation and gene expression effects. According to a 2012 study in Genome Biology, GHK-Cu can reset the activity of 4,000+ genes to a more youthful pattern. (DOI: 10.1186/gb-2012-13-11-r80)
- FOXO4-DRI — A senolytic peptide designed to selectively kill senescent ("zombie") cells. Showed dramatic results in mice (restoring fur growth, kidney function, fitness). No human trials yet.

Evidence level: Early-stage for most. Epithalon has limited human data from Russian clinical work. FOXO4-DRI is pre-clinical only. GHK-Cu has the most evidence for topical skin applications.

👉 Read our complete guide to anti-aging peptides →

Performance Peptides

These peptides are used by people looking to build muscle, improve recovery, and enhance physical performance. Most work by increasing growth hormone (GH) output.

How they work: Growth hormone secretagogues (GHS) signal your pituitary gland to release more of your own growth hormone. Unlike injecting synthetic GH directly, these peptides work with your body's natural feedback loops.

Key peptides in this group:
- CJC-1295 — A modified version of GHRH (growth hormone-releasing hormone). Comes in two forms: with DAC (longer-lasting) and without DAC (shorter pulses).
- Ipamorelin — A selective growth hormone releasing peptide (GHRP). Popular because it stimulates GH release without significantly affecting cortisol or prolactin (unlike older GHRPs).
- GHRP-6 — An older GHRP that strongly stimulates appetite and GH release. Often used for bulking.
- Tesamorelin — FDA-approved for reducing excess abdominal fat in HIV patients. The only GH-releasing peptide with full FDA approval.
- MK-677 (Ibutamoren) — Technically not a peptide (it's a small molecule), but often grouped with peptides because it mimics ghrelin and stimulates GH release orally.

Evidence level: Moderate to strong. CJC-1295 and ipamorelin have multiple clinical studies. Tesamorelin is FDA-approved. MK-677 has strong data but notable side effects (blood sugar issues, water retention).

👉 Read our complete guide to performance peptides →

Cognitive Peptides (Nootropic Peptides)

These target brain function: memory, focus, mood, and neuroprotection.

How they work: Most cognitive peptides work by modulating brain-derived neurotrophic factor (BDNF), a protein that supports the growth and survival of brain cells. Others affect neurotransmitters like dopamine, serotonin, or GABA.

Key peptides in this group:
- Semax — A synthetic analog of ACTH (a stress hormone fragment). Approved in Russia for stroke recovery and cognitive enhancement. Increases BDNF levels. Usually administered as a nasal spray.
- Selank — A synthetic analog of tuftsin (an immune peptide). Also approved in Russia, primarily for anxiety. Works on GABA and serotonin pathways. Nasal spray delivery.
- Dihexa — An extremely potent compound (active at picomolar concentrations) that may enhance memory by increasing hepatocyte growth factor (HGF) signaling. Only tested in animals. No human safety data.
- P21 — A BDNF-mimetic peptide. Increases neurogenesis (new brain cell growth) in animal studies. Very limited data.

Evidence level: Moderate for Semax and Selank (approved in Russia, multiple studies). Very weak for Dihexa and P21 (animal studies only, no human safety data).

👉 Read our complete guide to cognitive peptides →

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Are Peptides Legal? FDA Status Explained

This is one of the most confusing topics in the peptide world. The short answer: it depends on the peptide, how it's sold, and what country you're in.

FDA-Approved Peptides

Some peptides are fully approved prescription drugs. Your doctor can prescribe them, insurance may cover them, and they go through the same rigorous testing as any other medicine.

Examples of FDA-approved peptides:
- Semaglutide (Ozempic, Wegovy, Rybelsus) — For diabetes and weight loss
- Tirzepatide (Mounjaro, Zepbound) — For diabetes and weight loss
- Tesamorelin (Egrifta) — For HIV-related lipodystrophy
- Bremelanotide/PT-141 (Vyleesi) — For female sexual dysfunction
- Insulin — For diabetes (the original peptide drug)

These are manufactured to pharmaceutical-grade standards with strict quality control.

Research Peptides: The Gray Area

Many popular peptides (BPC-157, TB-500, CJC-1295, Ipamorelin, Semax, Selank) are not FDA-approved for human use. They're sold as "research chemicals" with labels that say "not for human consumption."

This doesn't mean they're illegal to possess in most countries. It means:
- They haven't gone through FDA clinical trials
- No doctor can legally prescribe them (with some exceptions through compounding)
- Quality control varies enormously between suppliers
- You are essentially an unmonitored test subject if you use them

The Gray Market

The gray market is where most non-prescription peptides are bought and sold. This includes:
- Online vendors selling "research peptides"
- Chinese manufacturers shipping directly
- Compounding pharmacies (a middle ground with more oversight)

The FDA is tightening regulations in 2026. Several major peptide vendors have already shut down. The FDA's HFP (Human Foods Program) priorities list now includes more peptide compounds. Compounding pharmacies face new restrictions on making copies of commercially available drugs like semaglutide.

👉 Read: Why Peptide Vendors Are Closing in 2026 →
👉 Read: Are Peptides Legal? The Complete Guide →

Legality by Country (Quick Overview)

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How to Use Peptides Safely

⚠️ Important: This section is for educational purposes only. We are not recommending you use any peptide. If you're considering peptide therapy, work with a licensed healthcare provider.

The Safest Path: Prescription Through a Doctor

The safest way to access peptides is through a licensed physician or telehealth provider who can:
- Evaluate whether a peptide is appropriate for your situation
- Monitor your bloodwork and health markers
- Prescribe FDA-approved peptides or work with legitimate compounding pharmacies
- Adjust dosing based on your response

👉 Read: Can You Get Peptides Through Telemedicine? →

Injection Basics

Most research peptides are given as subcutaneous (under the skin) injections. If your doctor prescribes an injectable peptide, they'll teach you proper technique. Key points include:

• Reconstitution — Most peptides come as a freeze-dried powder that must be mixed with bacteriostatic water
• Storage — Most reconstituted peptides need refrigeration and have a limited shelf life (typically 30 days)
• Injection sites — Usually the belly fat, thigh, or upper arm. Rotate sites to avoid irritation
• Sterility — Use alcohol swabs, clean needles, and proper technique to prevent infection

Oral vs Injectable: Pros and Cons

👉 Read: Oral Wegovy vs Injectable Semaglutide →

Reading a Certificate of Analysis (COA)

If you're buying research peptides, the COA is your best defense against low-quality or fake products. A COA from a third-party lab should show:

• HPLC purity — Look for 98%+ purity. Below 95% is a red flag.
• Mass spectrometry — Confirms the peptide is the correct molecule (right molecular weight).
• Endotoxin testing — Especially important for injectable peptides. Endotoxins can cause fever and serious reactions.
• Heavy metals — Should be below detectable limits.

Red flags: COAs from the vendor's own lab (not third-party), missing test dates, suspiciously round numbers, or no lab name/contact information.

👉 Read: How to Read a Peptide COA — Step by Step →

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Side Effects and Risks

Every peptide carries risks. Some are well-documented; others are unknown because the research simply hasn't been done. Here are the general categories:

Common Side Effects (GLP-1 Peptides)

The most widely studied peptides are the GLP-1 agonists (semaglutide, tirzepatide). Their side effects are well-documented:

• Nausea — The #1 reported side effect. Usually worst in the first few weeks and improves with time. Affects 40-50% of users at higher doses.
• Diarrhea and constipation — GI effects are common because these peptides slow digestion.
• Injection site reactions — Redness, swelling, or itching where you inject. Usually mild.
• Headache and fatigue — Especially during dose escalation.

Serious Risks (GLP-1 Peptides)

• Pancreatitis — Inflammation of the pancreas. Rare but serious. According to the FDA prescribing information for semaglutide, cases have been reported in clinical trials.
• Gallbladder problems — Rapid weight loss (from any cause) increases gallstone risk.
• Thyroid tumors — Semaglutide and tirzepatide carry a boxed warning about thyroid C-cell tumors in rodents. It's unknown whether this applies to humans. People with a personal or family history of medullary thyroid carcinoma should NOT use these drugs.
• Muscle loss — Losing weight fast can mean losing muscle too. A 2024 study in Obesity found that about 40% of weight lost on semaglutide was lean mass. (DOI: 10.1002/oby.23932)

Unknown Risks (Research Peptides)

For peptides like BPC-157, TB-500, and most others that lack human trials:

• We don't know the full side effect profile. Animal studies don't always predict human reactions.
• Cancer risk is debated. Peptides that promote blood vessel growth (like BPC-157) could theoretically feed existing tumors. This hasn't been proven, but it also hasn't been ruled out.
• Long-term effects are unknown. Most animal studies last weeks. Nobody knows what happens after years of use.
• Contamination risk. Research peptides from unregulated sources may contain bacteria, heavy metals, or the wrong compound entirely.
• Drug interactions are unstudied. If you take medications, the interactions with most research peptides are simply unknown.

Who Should NOT Use Peptides

• People with active cancer or a history of certain cancers (especially thyroid)
• Pregnant or breastfeeding women
• Children and teenagers (unless prescribed by a specialist)
• People with a history of pancreatitis (for GLP-1 peptides)
• Anyone with serious kidney or liver disease (most peptides are cleared by these organs)
• People on blood thinners (some peptides may affect clotting)

The bottom line: If a peptide hasn't been through human clinical trials, you are the experiment. Proceed with extreme caution, and always involve a healthcare provider.

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The Future of Peptide Science

The peptide world is evolving fast. Here's what's coming:

Oral Peptides Are Getting Better

The biggest limitation of peptides — that you have to inject them — is being solved. Novo Nordisk's oral semaglutide was just the beginning. A new high-dose oral formulation (oral Wegovy) is showing weight loss results comparable to the injection. Other companies are developing oral versions of tirzepatide and entirely new oral peptides.

According to a 2024 review in Nature Reviews Drug Discovery, over 30 oral peptide formulations are currently in clinical development. (DOI: 10.1038/s41573-024-00860-0)

Multi-Target Peptides

Single-target peptides are giving way to multi-target ones:
- Tirzepatide hits 2 receptors (GLP-1 + GIP)
- Retatrutide hits 3 receptors (GLP-1 + GIP + glucagon)
- Survodutide targets glucagon + GLP-1

These multi-agonists are showing dramatically better results than single-target peptides in clinical trials.

AI-Designed Peptides

Machine learning is accelerating peptide discovery. Companies are using AI to:
- Predict which amino acid sequences will fold into effective shapes
- Design peptides with better stability and bioavailability
- Find new therapeutic targets

According to a 2024 study in Nature Biotechnology, AI-designed peptides can now be created in weeks instead of years. (DOI: 10.1038/s41587-024-02123-4)

Regulatory Changes

The FDA is paying more attention to peptides than ever before. In 2026:
- The compounding loophole for drugs like semaglutide is closing
- More peptides are being added to the FDA's "difficult to compound" list
- Increased enforcement against gray-market vendors

This means access to research peptides may become harder, but the quality and safety of available peptides should improve.

👉 Read: Why Peptide Vendors Are Closing in 2026 →
👉 Read: The 2026 Compounded Semaglutide Ban Explained →

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Peptide Terminology Glossary

New to peptides? Here are the terms you'll see most often:

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Frequently Asked Questions (FAQ)

What are peptides in simple terms?

Peptides are short chains of amino acids — usually between 2 and 50 amino acids long. They're like mini-proteins. Your body makes thousands of them naturally to control things like hunger, healing, growth, and mood.

Are peptides safe?

It depends on the peptide. FDA-approved peptides like semaglutide have gone through rigorous clinical trials and have well-documented safety profiles. Research peptides like BPC-157 have much less human safety data. The source also matters — peptides from unregulated vendors may contain contaminants. Always consult a doctor.

Are peptides legal?

FDA-approved peptides are legal with a prescription. Research peptides are legal to purchase in most countries for research purposes, but using them on yourself exists in a legal gray area. Laws vary by country. Read our full guide on peptide legality →

Do peptides require a prescription?

FDA-approved peptides (semaglutide, tirzepatide, tesamorelin, etc.) require a prescription. Research peptides do not, but they're sold labeled "not for human consumption."

How are peptides different from steroids?

Peptides signal your body to produce its own hormones (like growth hormone). Steroids ARE synthetic hormones that directly replace what your body makes. Peptides generally have fewer and milder side effects than steroids, but they also produce smaller effects. They are fundamentally different classes of compounds.

Can you take peptides orally?

Most peptides are destroyed by stomach acid, so they need to be injected. The notable exception is oral semaglutide (Rybelsus/oral Wegovy), which uses a special absorption enhancer. A few others can be taken as nasal sprays (Semax, Selank) or topical creams (GHK-Cu). Read: Oral vs Injectable Semaglutide →

What is the most popular peptide?

As of 2026, semaglutide is by far the most popular peptide, driven by the Ozempic/Wegovy weight loss phenomenon. Among research peptides, BPC-157 is the most popular, especially in the biohacking and athletic communities.

How much do peptides cost?

Costs vary enormously. Brand-name semaglutide (Wegovy) can cost $1,000-1,500/month without insurance. Compounded versions were cheaper ($200-400/month) before the FDA crackdown. Research peptides from online vendors range from $30-100 per vial, depending on the peptide and quantity. Use our peptide calculator →

What are the side effects of peptides?

Side effects depend on the specific peptide. GLP-1 peptides commonly cause nausea, diarrhea, and constipation. Growth hormone peptides can cause water retention, joint pain, and blood sugar changes. Research peptides have poorly documented side effects due to lack of human trials.

Can peptides cause cancer?

This is a legitimate concern, especially for peptides that promote blood vessel growth (angiogenesis) like BPC-157, or those that stimulate cell growth like growth hormone peptides. There is no definitive evidence that these peptides cause cancer in humans, but there is also no evidence proving they don't. GLP-1 peptides carry a warning about thyroid tumors in rodents. If you have a history of cancer, talk to your oncologist before using any peptide.

How long do peptides take to work?

It varies. Semaglutide typically shows noticeable appetite suppression within the first week, with significant weight loss over 3-6 months. Growth hormone peptides may take 4-8 weeks to show effects. BPC-157 users often report improvements in healing within 1-2 weeks, though this is anecdotal.

What's the difference between Ozempic and Wegovy?

Both contain semaglutide. Ozempic is approved for type 2 diabetes (max dose 2 mg/week). Wegovy is approved for weight loss (max dose 2.4 mg/week). Same molecule, different doses and FDA indications.

Are peptides the same as SARMs?

No. Peptides are chains of amino acids. SARMs (Selective Androgen Receptor Modulators) are synthetic chemicals that mimic testosterone. They work through completely different mechanisms. SARMs are not FDA-approved and carry their own serious risks.

Where can I buy peptides?

FDA-approved peptides come from pharmacies with a prescription. Research peptides are available from online vendors, though many are shutting down due to regulatory pressure. The safest route is always through a healthcare provider. Read: How to Buy Peptides Safely →

What should I look for in a peptide vendor?

Third-party testing (COA from an independent lab), transparent business practices, proper storage and shipping (cold chain), customer reviews from multiple sources, and clear labeling. Avoid vendors who make health claims or suggest dosing for human use. Read: How to Read a Peptide COA →

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Compare Peptides Side by Side

Want to compare specific peptides? Use our free comparison tool:

👉 Compare any two peptides →
👉 Peptide dose calculator →

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References

1. Lau JL, Dunn MK. "Therapeutic peptides: Historical perspectives, current development trends, and future directions." Bioorganic & Medicinal Chemistry. 2018;26(10):2700-2707. DOI: 10.1016/j.bmc.2017.06.052

2. Muttenthaler M, et al. "Trends in peptide drug discovery." Nature Reviews Drug Discovery. 2021;20(4):309-325. DOI: 10.1038/s41573-020-00135-8

3. Granhall C, et al. "Pharmacokinetics, Safety, and Tolerability of Oral Semaglutide." Clinical Pharmacokinetics. 2019;58(4):509-522. DOI: 10.1007/s40262-019-00827-4

4. Wilding JPH, et al. "Once-Weekly Semaglutide in Adults with Overweight or Obesity." New England Journal of Medicine. 2021;384(11):989-1002. DOI: 10.1056/NEJMoa2032183

5. Jastreboff AM, et al. "Tirzepatide Once Weekly for the Treatment of Obesity." New England Journal of Medicine. 2022;387(3):205-216. DOI: 10.1056/NEJMoa2206038

6. Sikiric P, et al. "BPC 157: Unique Peptide Sequence and Evidence for Healing." Current Pharmaceutical Design. 2018;24(18):1935-1973. DOI: 10.2174/1381612824666180713101833

7. Pickart L, Margolina A. "Regenerative and Protective Actions of GHK-Cu Copper Peptide." International Journal of Molecular Sciences. 2012;13(11):14002-14015. DOI: 10.3390/ijms131114002

8. Khavinson VK. "Peptide Regulation of Ageing." Advances in Gerontology. 2020;10(1):11-17. DOI: 10.1134/S2079057020010087

9. Fricker LD. "Neuropeptides and Other Bioactive Peptides: From Discovery to Function." Colloquium Series on Neuropeptides. 2012;1(1):1-122.

10. Wang L, et al. "Therapeutic peptides: current applications and future directions." Signal Transduction and Targeted Therapy. 2022;7(1):48. DOI: 10.1038/s41392-022-00904-4

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Last updated: February 2026

This article was written by the Peptok Research Team and reviewed for accuracy. It is not medical advice. Always consult a qualified healthcare provider before making decisions about peptide use.