Guide

Peptide Category Explainers: How Every Compound Class on This Site Is Defined

This site tracks dozens of compounds, and each one is assigned to a category that reflects its primary biological mechanism and intended research context. These categories are not rigid pharmacological classifications: some compounds could reasonably be placed in more than one group: but they provide a consistent framework for understanding why certain compounds are grouped together and how they relate to each other. This guide explains each of the nine categories used on the site: what the category means, the shared mechanism across its members, which compounds are currently tracked within it, and a summary of the regulatory landscape. The categories are: GLP-1 receptor agonists, growth hormone releasing peptides (GHRP), growth hormone releasing hormones (GHRH), recovery peptides, cognitive peptides, immune peptides, skin and cosmetic peptides, longevity compounds, and small molecules. For each category, the goal is to give readers a clear mental model so that when they encounter a compound name elsewhere on the site, they can immediately place it in context.

GLP-1 Receptor Agonists

GLP-1 receptor agonists are compounds that mimic or enhance the action of glucagon-like peptide-1, an incretin hormone naturally secreted by L-cells in the intestine in response to food. GLP-1 stimulates insulin secretion, suppresses glucagon, slows gastric emptying, and promotes satiety: all in a glucose-dependent manner. Native GLP-1 has a half-life of approximately two minutes due to rapid degradation by the DPP-4 enzyme, so pharmaceutical GLP-1 agonists are engineered for extended half-lives through amino acid modifications, fatty acid conjugation, or albumin binding. This category on the site includes both single GLP-1 receptor agonists and multi-receptor agonists that also target GIP and/or glucagon receptors, since they are commonly grouped together in public discussion and share overlapping clinical contexts. These are among the most heavily researched and widely prescribed compounds tracked on this site, with multiple FDA approvals for Type 2 diabetes and chronic weight management.

Key points

• GLP-1 receptor agonists mimic the incretin hormone GLP-1, which stimulates insulin secretion, suppresses glucagon, slows gastric emptying, and promotes satiety: all in a glucose-dependent manner.
• Semaglutide (Ozempic, Wegovy, Rybelsus) is FDA-approved for Type 2 diabetes and chronic weight management, with the STEP 1 trial showing approximately 15% weight loss at 68 weeks.
• Tirzepatide (Mounjaro, Zepbound) is a dual GIP/GLP-1 receptor agonist FDA-approved for Type 2 diabetes, chronic weight management, and moderate-to-severe obstructive sleep apnea in adults with obesity.
• Retatrutide is an investigational triple GIP, GLP-1, and glucagon receptor agonist. The Phase 2 12 mg result was -17.5% at week 24 and -24.2% at week 48. Lilly reported positive Phase 3 obesity results in 2026, but the drug remains unapproved.
• These compounds have generated enormous public discussion and social media attention, requiring careful separation of clinical trial data from community claims about off-label and compounded use.
• The FDA has issued warning letters related to compounded and research-use-only GLP-1 peptide marketing, and the regulatory landscape for compounded GLP-1 products remains active.

Growth Hormone Releasing Peptides (GHRP)

Growth hormone releasing peptides (GHRPs) are a class of synthetic peptides that stimulate growth hormone release through the ghrelin receptor: also called the growth hormone secretagogue receptor (GHS-R). This is a different pathway from growth hormone releasing hormone (GHRH), which acts through its own dedicated receptor. GHRPs mimic the action of ghrelin, the endogenous ligand for the GHS-R, and were among the first compounds identified that could stimulate GH release without directly administering growth hormone itself. Despite extensive pharmacological characterization, no GHRP has ever received FDA approval for any indication. The most widely discussed GHRP on this site is ipamorelin, a first-generation pentapeptide identified in the late 1990s. MK-677 (ibutamoren) is mechanistically related: it is an orally active, non-peptide ghrelin receptor agonist: and is often discussed alongside GHRPs despite not being a peptide itself. AOD-9604, an HGH fragment peptide, is also grouped nearby because it relates to the growth hormone axis, though it acts through a lipolytic mechanism rather than GH release.

Key points

• GHRPs stimulate growth hormone release through the ghrelin receptor (GHS-R), a distinct pathway from GHRH analogs which act through the GHRH receptor.
• Ipamorelin is a synthetic pentapeptide GHRP widely discussed in fitness and anti-aging communities, often described as the 'safest GHS' based on preclinical selectivity data: this framing is a community interpretation, not a regulatory consensus.
• MK-677 (ibutamoren) is an oral, non-peptide ghrelin receptor agonist developed by Merck with published Phase 2 data showing IGF-1 increases, but it was never submitted for FDA approval and development was discontinued.
• AOD-9604 is a C-terminal fragment of human growth hormone (residues 177-191) designed for lipolytic activity; its Phase 2 obesity trials failed to meet primary weight loss endpoints and development was discontinued.
• No GHRP or GHS-class compound has received FDA approval for any indication.
• The CJC-1295 + ipamorelin combination is one of the most discussed peptide stacks in online fitness and telehealth communities, based on theoretical synergy between GHRH and GHS pathways, but lacks clinical trial data for the combination.

Growth Hormone Releasing Hormones (GHRH)

Growth hormone releasing hormone (GHRH) is a peptide hormone produced in the hypothalamus that stimulates the anterior pituitary gland to secrete growth hormone. Synthetic GHRH analogs are designed to mimic this endogenous hormone and stimulate endogenous GH release, which in turn increases IGF-1 levels. This category includes the only growth hormone secretagogue-class peptide with current FDA approval: tesamorelin (Egrifta), approved for HIV-associated lipodystrophy. It also includes CJC-1295, a synthetic GHRH analog developed with drug affinity complex (DAC) technology for extended half-life that was never submitted for FDA approval, and sermorelin, a formerly FDA-approved diagnostic agent for pediatric growth hormone deficiency whose brand product (Geref) was discontinued by the manufacturer. GHRH analogs are mechanistically distinct from GHRPs: they act through a different receptor: and the two classes can have additive effects on GH release when studied together, which is the rationale for the common CJC-1295 + ipamorelin community protocol.

Key points

• GHRH analogs stimulate endogenous growth hormone release through the GHRH receptor in the pituitary: a different receptor from GHRPs, which act through the ghrelin receptor.
• Tesamorelin (Egrifta) is the only GHRH/GHS-class peptide with current FDA approval, indicated for reduction of excess visceral abdominal fat in HIV-infected patients with lipodystrophy, based on a Phase 3 trial published in NEJM (2010).
• CJC-1295 is a synthetic GHRH analog with DAC technology for extended half-life; it was developed by ConjuChem but clinical development was discontinued and it was never submitted for FDA approval.
• Sermorelin is a 29-amino-acid GHRH fragment that was formerly FDA-approved as Geref for diagnostic use in pediatric growth hormone deficiency; the manufacturer discontinued the brand product, and it is now widely compounded by telehealth clinics for off-label adult use.
• Two forms of CJC-1295 exist in community discussions: with DAC (extended half-life) and without DAC (modified GRF 1-29); both are research-use-only and not FDA-approved.
• The GHRH + GHRP combination (e.g., CJC-1295 + ipamorelin) is based on theoretical receptor synergy but has no FDA-approved clinical data for the combination.

Recovery Peptides

Recovery peptides are a functional grouping rather than a single receptor family: these are compounds discussed primarily in the context of tissue repair, injury recovery, and wound healing. On this site, the two primary recovery peptides are BPC-157 and TB-500. BPC-157 is a pentadecapeptide derived from human gastric juice that has been studied in animal models for tendon, ligament, and muscle healing, but has no published human clinical trials and no FDA approval. TB-500 is a synthetic version of a fragment of thymosin beta-4, a naturally occurring peptide involved in actin binding and cell migration, and is similarly discussed in injury recovery contexts without FDA approval. Both compounds are widely sold as research-use-only chemicals and are among the most discussed peptides in online fitness and recovery communities. Several recovery peptides, including BPC-157 and TB-500, were scheduled for discussion at the July 2026 FDA Pharmacy Compounding Advisory Committee meeting, reflecting regulatory interest in the compounding of these substances.

Key points

• Recovery peptides are grouped by functional context (tissue repair, injury recovery) rather than a shared receptor or mechanism.
• BPC-157 is a pentadecapeptide derived from human gastric juice discussed in online recovery communities; it has no published human clinical trials and no FDA approval.
• TB-500 is a synthetic fragment of thymosin beta-4, a peptide involved in actin binding and cell migration; it is also not FDA-approved and has no published human clinical trials for recovery.
• Both BPC-157 and TB-500 were scheduled for FDA Pharmacy Compounding Advisory Committee discussion in July 2026, indicating active regulatory scrutiny.
• The FDA has identified certain bulk peptide substances as potentially presenting significant safety risks in compounding contexts, which applies to these recovery peptides.
• Online claims about recovery peptides should be treated as source-discovery signals, not proof of efficacy: the evidence base is predominantly preclinical.

Cognitive Peptides

Cognitive peptides are compounds discussed primarily in the context of cognitive enhancement, neuroprotection, and attention. This is a diverse group spanning different mechanisms and evidence levels. Semax is a heptapeptide ACTH analog registered as a medicine in Russia for cognitive and attention-enhancing effects, with studies primarily from Russian institutions and no FDA approval. Selank is a synthetic heptapeptide tuftsin analog registered in Russia as an anxiolytic, with predominantly Russian-language preclinical and limited clinical literature. Noopept is a dipeptide nootropic registered as a pharmaceutical in Russia for mild cognitive impairment, sold as a supplement in the US without FDA drug approval. Dihexa is an angiotensin IV analog developed to activate the HGF/c-Met receptor system, studied only in animal models with no human clinical trials. Cerebrolysin is a porcine brain-derived peptide preparation approved in over 40 countries for neurological indications including stroke and dementia, but not FDA-approved in the United States. The common thread is that all of these compounds are discussed in biohacking and cognitive enhancement communities, but their evidence bases vary widely: from small Russian clinical trials to purely preclinical animal data.

Key points

• Cognitive peptides are grouped by functional context (cognitive enhancement, neuroprotection) rather than a shared mechanism: they span ACTH analogs, tuftsin analogs, dipeptide nootropics, angiotensin IV analogs, and brain-derived preparations.
• Semax is an ACTH analog registered as a medicine in Russia; its clinical studies are primarily Russian-language and lack independent Western replication.
• Selank is a tuftsin analog registered in Russia as an anxiolytic; its evidence base is predominantly preclinical with limited Russian clinical literature.
• Noopept is a dipeptide nootropic registered as a pharmaceutical in Russia for mild cognitive impairment; it is sold as a dietary supplement in the US without FDA drug approval.
• Dihexa is an angiotensin IV analog that activates the HGF/c-Met receptor system; it has been studied only in animal models with no human clinical trials. The widely circulated '10 million times stronger than BDNF' claim is an extrapolation from a single rat study and has not been validated in humans.
• Cerebrolysin is a porcine brain-derived peptide preparation approved in 40+ countries for stroke and dementia but not FDA-approved in the United States; a Cochrane review noted inconsistent results for vascular dementia.
• None of these compounds are FDA-approved for cognitive enhancement, and the evidence ranges from small Russian clinical trials to purely preclinical animal data.

Immune Peptides

Immune peptides are compounds discussed primarily in the context of immune modulation, antimicrobial activity, and inflammatory response. This category includes thymosin alpha-1, LL-37, and KPV: three compounds with distinct mechanisms that share an immunological context. Thymosin alpha-1 is a naturally occurring thymic peptide that modulates immune function by enhancing T-cell maturation, dendritic cell activity, and cytokine production. It is marketed as Zadaxin and is approved in over 30 countries for chronic hepatitis B, hepatitis C, and as an immune adjuvant, but is not FDA-approved in the United States. LL-37 is the sole human cathelicidin antimicrobial peptide, with well-characterized broad-spectrum activity against bacteria, fungi, and enveloped viruses in laboratory studies, but no FDA-approved therapeutic products. KPV is a tripeptide (Lys-Pro-Val) derived from alpha-melanocyte-stimulating hormone (alpha-MSH) with reported anti-inflammatory effects in preclinical animal models, but no published human clinical trials. All three are tracked as regulatory watch items, with BPC-157 and several other peptides also scheduled for FDA advisory committee discussion.

Key points

• Immune peptides are grouped by functional context (immune modulation, antimicrobial activity, anti-inflammatory effects) rather than a shared mechanism.
• Thymosin alpha-1 is approved in 30+ countries as Zadaxin for hepatitis B/C and immune adjuvant use but has never received FDA approval in the United States, despite Fast Track designation for certain oncology indications and over 100 registered clinical trials.
• LL-37 is the only human cathelicidin antimicrobial peptide, with broad-spectrum activity against bacteria, fungi, and viruses in laboratory studies, but no FDA-approved therapeutic products exist in the United States.
• KPV is a tripeptide derived from alpha-MSH with reported anti-inflammatory effects in preclinical animal models; no human clinical trials have been published.
• All three immune peptides are not FDA-approved and are sold as research-use-only chemicals; the biohacking community has adopted them for self-directed immune support despite the absence of clinical trial evidence.
• KPV and several other peptides were scheduled for FDA Pharmacy Compounding Advisory Committee discussion in July 2026.

Skin and Cosmetic Peptides

Skin and cosmetic peptides are compounds used primarily in topical skincare formulations for proposed effects on collagen production, wrinkle appearance, and skin repair. GHK-Cu has a mixed record: a broad author-linked review covers cellular, animal, and cosmetic research, while a randomized topical study completed by 13 participants found no objective post-laser advantage despite higher patient satisfaction. Argireline (acetyl hexapeptide-8) is a synthetic hexapeptide fragment of SNAP-25 marketed as a topical 'Botox alternative.' Matrixyl (palmitoyl pentapeptide-4) is a matrikine peptide used in anti-wrinkle cosmetics. Cosmetic, medical, and injectable claims require different evidence and regulatory analysis. FDA's withdrawn-nomination table separately identifies limited human safety data for injectable GHK-Cu; GHK-Cu is not in the page's active Category 2 table.

Key points

• Skin and cosmetic peptide claims often involve topical products, but evidence remains ingredient- and formulation-specific.
• GHK-Cu has a broad 2015 author-linked review, but the small completed randomized topical study found no objective post-laser advantage.
• Argireline (acetyl hexapeptide-8) is a SNAP-25 fragment marketed as a topical 'Botox alternative'; one RCT supports modest wrinkle reduction after 4 weeks of topical use, but it should not be equated to botulinum toxin injections.
• Matrixyl (palmitoyl pentapeptide-4) is a matrikine peptide with clinical evidence for modest improvement in fine lines and wrinkles from a 12-week controlled study (Robinson et al., 2005).
• Topical cosmetic evidence should not be carried into medical, injectable, or systemic claims without route- and formulation-specific support.
• The palmitoyl chain in Matrixyl improves skin penetration of the peptide, as confirmed by in vitro permeation studies: this is mechanistic evidence, not proof of clinical efficacy.

Longevity Compounds

Longevity compounds are substances discussed primarily in the context of extending lifespan, delaying age-related disease, and promoting healthspan. This is a heterogeneous category that includes both peptides and non-peptide molecules, unified by their proposed geroprotective mechanisms rather than a shared receptor or pathway. Rapamycin (sirolimus) is an FDA-approved mTOR inhibitor used for transplant rejection prophylaxis and lymphangioleiomyomatosis (LAM); it is the most discussed longevity therapeutic based on robust lifespan extension in mice (NIA ITP studies) but has no FDA approval for aging. NAD+ precursors (NR and NMN) are widely promoted to restore declining NAD+ levels and support sirtuin-mediated longevity pathways; NR is FDA-GRAS as a supplement, while NMN is subject to an FDA DSHEA exclusion determination. Spermidine is a naturally occurring polyamine that induces autophagy and has shown preliminary cognitive benefits in the SmartAge trial. Epitalon is a Russian-developed peptide with telomerase activation claims from a single research group, lacking independent Western replication. Metformin, while technically a small molecule, is often discussed in longevity contexts due to its AMPK activation and the ongoing TAME trial. The key challenge for this category is separating biomarker changes (e.g., raised NAD+, increased telomerase) from proven clinical outcomes, and separating preclinical mouse data from human evidence.

Key points

• Longevity compounds are grouped by proposed geroprotective function (lifespan extension, healthspan, age-related disease delay) rather than a shared mechanism: they include mTOR inhibitors, NAD+ precursors, polyamines, and peptides.
• Rapamycin (sirolimus) is FDA-approved for transplant rejection prophylaxis and LAM, and is the most discussed longevity therapeutic based on NIA ITP mouse lifespan data, but off-label use for aging is not FDA-approved and remains controversial.
• NAD+ precursors (NR and NMN) raise blood NAD+ in humans, but clinical outcome benefits remain inconsistent; NR is FDA-GRAS as a supplement, while NMN is subject to an FDA DSHEA exclusion determination.
• Spermidine is a naturally occurring polyamine that induces autophagy; the SmartAge RCT showed memory improvements in older adults with subjective cognitive decline, but no human lifespan data exists.
• Epitalon is a peptide with telomerase activation claims from the Khavinson research group; these claims lack independent Western replication and should not be presented as established anti-aging evidence.
• No completed randomized controlled trial has demonstrated lifespan extension in humans for any compound in this category; the evidence base ranges from observational associations to preclinical mouse data to small human biomarker trials.

Small Molecules

Small molecules on this site are non-peptide organic compounds that are tracked alongside peptides because they appear in the same research, biohacking, and longevity discussions. These compounds are not peptides: they are not chains of amino acids: but they share overlapping communities of interest and are often discussed in the same contexts. Metformin is an FDA-approved biguanide antidiabetic that activates AMPK and is sometimes called 'poor man's rapamycin' in longevity circles; the TAME trial is investigating whether it can delay age-related disease onset in non-diabetic adults. Methylene blue is an FDA-approved medication for methemoglobinemia that has gained biohacking attention for proposed cognitive and mitochondrial benefits at low doses, supported only by preclinical data. 5-Amino-1MQ is a small molecule inhibitor of nicotinamide N-methyltransferase (NNMT) that has been promoted as 'exercise in a pill' based on preclinical mouse studies showing reversal of diet-induced obesity; no human clinical trials exist. The regulatory status of these compounds varies widely: from FDA-approved drugs with established safety profiles to research chemicals with no human safety data.

Key points

• Small molecules on this site are non-peptide organic compounds tracked alongside peptides because they appear in the same research and biohacking communities.
• Metformin is an FDA-approved biguanide antidiabetic that activates AMPK; the TAME trial is testing whether it can delay age-related disease in non-diabetic adults, but no completed RCT has demonstrated lifespan extension in humans.
• Methylene blue is FDA-approved for methemoglobinemia (Provayblue) but biohacking use for cognitive enhancement and mitochondrial function is off-label and supported only by preclinical data; non-pharmaceutical-grade products raise significant quality concerns.
• 5-Amino-1MQ is an NNMT inhibitor promoted as 'exercise in a pill' based exclusively on mouse studies; no human clinical trials have been published and it is not FDA-approved.
• The regulatory status of small molecules in this category ranges from FDA-approved drugs (metformin, methylene blue) to unapproved research chemicals (5-amino-1MQ).
• Observational data for metformin (e.g., reduced mortality in diabetic patients) should not be presented as causal evidence of longevity benefit in non-diabetics: confounding is a significant limitation of retrospective studies.

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