LL-37 (Cathelicidin)

Semaglutide, while primarily known as the active ingredient in Ozempic and Wegovy, is fundamentally a peptide — a 31 amino acid modified GLP-1 analog. Its inclusion in the peptide directory reflects its origin as a peptide therapeutic and its relevance to the peptide therapy community, many of whom access it through compounding pharmacies. Semaglutide represents the most commercially successful therapeutic peptide in history, with annual sales exceeding $20 billion. From a peptide science perspective, semaglutide is a masterwork of molecular engineering. It was designed with three key modifications to native GLP-1: an amino acid substitution at position 8 that resists DPP-4 enzyme degradation, a C18 fatty acid chain at position 26 that enables albumin binding (extending half-life to ~7 days), and an amino acid substitution at position 34 that prevents fatty acid attachment at the wrong position. These modifications transformed a peptide with a 2-minute half-life into one with a 7-day half-life. In the peptide community, compounded semaglutide has become the most discussed and widely used peptide, surpassing even BPC-157 and growth hormone secretagogues. The compounded form typically uses the same amino acid sequence but may differ in formulation, preservatives, and purity compared to the Novo Nordisk branded products. Quality varies significantly between compounding pharmacies, making potency testing and sterility verification critical.

Tirzepatide is a 39 amino acid dual GIP/GLP-1 receptor agonist peptide, marketed as Mounjaro and Zepbound by Eli Lilly. It represents a significant advance in peptide engineering, being the first approved twincretin — a single molecule that activates two incretin receptors simultaneously. Tirzepatide has achieved the highest weight loss results of any approved anti-obesity medication, with trials showing 22.5% body weight reduction. The peptide's design incorporates a C20 fatty diacid moiety linked via a linker to lysine at position 20, enabling albumin binding and a half-life of approximately 5 days. The molecule preferentially activates GIP receptors while also providing potent GLP-1 agonism. The GIP component appears to enhance fat cell metabolism and may contribute to the superior weight loss compared to GLP-1-only agonists like semaglutide. In the peptide community, compounded tirzepatide became extremely popular in 2024-2025 during the branded product shortage. The longer amino acid sequence (39 vs 31 for semaglutide) makes tirzepatide more challenging and expensive to compound. Quality concerns are amplified with tirzepatide compared to semaglutide due to the dual-receptor mechanism — slight structural variations could alter the GIP:GLP-1 activity ratio. Regulatory battles over compounded tirzepatide continue to shape the market.

GHK-Cu (glycyl-L-histidyl-L-lysine copper complex) is a naturally occurring tripeptide-copper complex found in human plasma, saliva, and urine. First identified in 1973 by Dr. Loren Pickart, it has become one of the most extensively studied peptides in skin science and regenerative medicine. Plasma levels of GHK naturally decline with age, from approximately 200 ng/mL at age 20 to just 80 ng/mL by age 60. This decline that correlates with reduced regenerative capacity of tissues. GHK-Cu operates through multiple interconnected mechanisms. The copper component enables enzymatic catalysis critical for collagen cross-linking, antioxidant defense, and cellular respiration. The peptide stimulates synthesis of collagen, elastin, and glycosaminoglycans while simultaneously modulating matrix metalloproteinases and their inhibitors to optimize tissue remodeling. Perhaps most remarkably, genomic studies have shown that GHK-Cu can up- and down-regulate at least 4,000 human genes, effectively shifting gene expression patterns toward a healthier, more youthful profile. A 2024 multicenter study[1] found that 0.05% GHK-Cu gel after fractional laser resurfacing produced 25% faster epithelial recovery with 30% reductions in inflammatory markers IL-1beta and TNF-alpha. GHK-Cu is available in both topical formulations (creams, serums) and injectable research preparations. It is not FDA-approved as a drug, but GHK-Cu is widely used in cosmetic skincare products as an active ingredient. Research continues to expand beyond skin applications into wound healing, hair growth stimulation, lung tissue remodeling, and potential anti-cancer effects through gene expression modulation. Its strong safety profile and natural occurrence in the body make it one of the most well-tolerated peptides in research.

BPC-157 (Body Protection Compound-157) is a synthetic pentadecapeptide consisting of 15 amino acids, derived from a protective protein found in human gastric juice. It has gained widespread attention in regenerative medicine research for its remarkable tissue-healing properties observed across more than 100 preclinical studies. The peptide promotes angiogenesis (new blood vessel formation), modulates the nitric oxide system, and accelerates the healing of tendons, ligaments, muscles, the gastrointestinal tract, and bone tissue in animal models. As of early 2026, the FDA has reclassified BPC-157 from Category 2 to Category 1 on the 503A Bulk Drug Substances List, meaning licensed compounding pharmacies can now legally prepare patient-specific formulations with a prescription. However, BPC-157 has no FDA-approved therapeutic indication. Human clinical data remains extremely limited, with only three small pilot studies published as of late 2025, all from the same research group and lacking placebo controls. A 2025 systematic review in the American Journal of Sports Medicine[1] screened 544 articles and found only one clinical study meeting inclusion criteria, with the remaining 35 studies being preclinical animal models. Despite the limited human evidence, the peptide is generally well-tolerated in research settings, though theoretical concerns exist about its pro-angiogenic effects potentially promoting tumor growth. BPC-157 remains on the WADA Prohibited List for competitive athletes.