Mechanism, trial history, and regulatory context for research peptides

GLP-1 receptor agonists have become one of the most talked-about drug classes of the past decade. This article walks through what they are, how they work, and what the peer-reviewed clinical research actually shows. It covers the first-generation single agonists like semaglutide, the dual agonist tirzepatide, and the investigational triple agonist retatrutide.

BPC-157 and TB-500 are two of the most discussed research peptides in recovery and sports medicine circles. Both are marketed informally as tissue repair peptides. This article walks through what the peer-reviewed literature actually shows, where the gaps are, and why the regulatory and anti-doping communities classify them the way they do.

Growth hormone secretagogues are compounds that cause the pituitary gland to release more of its own stored growth hormone. Instead of administering growth hormone directly, they work upstream by activating the natural signaling pathways that control its release. This article covers how the growth hormone axis actually works, the two main receptor families drug developers have targeted, and what the published research shows about the best-known compounds in each family.

Melanocortin peptides are a class of signaling molecules derived from a precursor protein called pro-opiomelanocortin, or POMC. They act on a family of five receptors that govern pigmentation, appetite, sexual function, inflammation, and energy expenditure. Two members of this class, Melanotan II and PT-141, are widely discussed in men's health and research communities. This article walks through how the melanocortin system actually works, what the published research shows about each compound, and how their regulatory status differs sharply from one another.

Amylin is a pancreatic hormone that most people have never heard of, even though it is released alongside insulin every time blood glucose rises after a meal. For decades, researchers knew that people with type 2 diabetes and obesity had impaired amylin signaling, but turning that observation into a useful therapy proved harder than expected. This article walks through what amylin actually does, why the first approved amylin analog required multiple daily injections, how Novo Nordisk engineered a once weekly version called cagrilintide, and what the published research shows about pairing it with semaglutide in the combination called CagriSema.

Thymosin alpha-1 and MOTS-c represent two very different approaches to questions about immune function and metabolic aging. One was isolated from thymus extracts in the 1970s and went on to earn regulatory approval in dozens of countries. The other was found hiding inside a stretch of mitochondrial DNA that researchers had previously assumed was non-coding. This article covers what each peptide is, where the evidence is strongest, and where gaps remain.

Most growth hormone secretagogues are peptides that must be injected because the digestive tract breaks them down before they can reach the bloodstream. MK-677, also known as ibutamoren, took a different approach: instead of a peptide structure, it uses a small non-peptide molecule that mimics ghrelin, binds the same pituitary receptor as injectable ghrelin mimetics, and survives oral administration. Merck brought MK-677 through multiple human clinical trials over roughly a decade before discontinuing the program. This article covers how the compound works, what those trials found, and what remains unknown or unresolved.

NAD+ is a coenzyme found in every living cell, and its role in energy metabolism has been understood for decades. What is newer is the recognition that NAD+ levels decline substantially with age, and that this decline may be connected to a broad set of age-related metabolic changes. NMN and NR are two orally available precursor molecules that researchers have studied as ways to replenish NAD+ levels. This article covers the underlying biology, what the published human trial data actually shows, and where the evidence remains incomplete.

Tesamorelin is a synthetic analog of growth hormone-releasing hormone and the only GHRH-class compound to receive FDA approval. That approval, granted in 2010, covers a specific indication: reducing excess abdominal fat in HIV-infected patients with lipodystrophy. Outside that setting, tesamorelin has been studied in several other populations and contexts, including general visceral adiposity, cognitive function, and non-alcoholic fatty liver disease. This article covers the biology, the clinical trial record, and where the evidence currently stands.

GHK-Cu is a copper-binding tripeptide that occurs naturally in human blood plasma, saliva, and urine. It was identified through biochemical research in the early 1970s and has since been studied across a broad range of contexts, from wound healing and collagen synthesis to skin aging and hair follicle biology. Unlike most research peptides in this space, GHK-Cu also has an established commercial presence in topical cosmetics, where copper peptide formulations have been marketed for decades. This article covers what the compound is, where the published research is strong, where it is preliminary, and how the topical and injectable research contexts differ.

Insulin-like growth factor 1 sits at the center of one of the most studied signaling axes in endocrinology. Growth hormone alone does not directly build muscle or regulate cellular metabolism. It does most of its work by telling the liver to produce IGF-1, which then circulates to tissues throughout the body. This article covers how that axis works, why researchers developed a modified version called IGF-1 LR3, what the clinical trial record looks like, and what the regulatory landscape means for anyone encountering this compound in a research context.

CJC-1295 and ipamorelin are two of the most widely discussed research peptides in the growth hormone axis category. They act through different but complementary mechanisms, which is why researchers often study them together. This article covers what each compound is, what the published literature reports, and where the current evidence ends.

AOD-9604 is a synthetic peptide corresponding to a short stretch of amino acids near the end of the human growth hormone sequence. Researchers developed it on the hypothesis that this fragment retained the fat-burning properties of full growth hormone while avoiding the hormone's growth-promoting and glucose-disrupting effects. This article covers what the peer-reviewed literature shows about that hypothesis, what the clinical trials found, and where the compound stands today.

Sermorelin is a synthetic peptide that mirrors the functional core of the body's own growth hormone-releasing hormone. It was the first compound in its class to receive FDA approval, cleared in 1997 for treating growth hormone deficiency in children. Though the original brand was eventually pulled from the market for commercial reasons, sermorelin has remained the subject of ongoing research in adults with age-related growth hormone decline. This article covers the biology, the clinical history, and what the published literature actually shows.

Tirzepatide arrived in clinical medicine as something genuinely novel: a single synthetic peptide designed to activate two separate incretin receptors at once. The results from its Phase 3 development programs were striking enough that they reset expectations for what pharmacological weight management could achieve. This article covers how the dual incretin mechanism works, what the SURPASS and SURMOUNT trial programs found, and what distinguishes tirzepatide from the single-receptor GLP-1 agonists that preceded it.

Semaglutide is the GLP-1 receptor agonist behind Ozempic, Wegovy, and Rybelsus. It was not the first drug in its class, but the scale of its clinical trial program and the results that program produced made it the reference compound against which newer agents are measured. This article covers what semaglutide is, how it works, what the STEP obesity trials found, and what the SELECT cardiovascular outcomes trial showed about its effects beyond weight and glucose.

Epithalon is a synthetic tetrapeptide that emerged from decades of Soviet and post-Soviet research into pineal gland extracts and aging biology. The compound sits at the intersection of two areas that have attracted serious scientific attention: telomere biology and the neuroendocrine regulation of aging. Most of the published research originates from a single laboratory at the St. Petersburg Institute of Bioregulation and Gerontology, which means the evidence base is narrower than its reputation in research peptide communities might suggest. This article covers what epithalon is, what the published data actually shows, and where the limitations are.

Retatrutide is an investigational peptide developed by Eli Lilly that activates three hormone receptors at once: GLP-1, GIP, and glucagon. Adding glucagon receptor activity to the incretin combination is a deliberate pharmacological move, not an oversight, and it changes the character of how the drug works compared with the dual agonists that came before it. Phase 2 data published in the New England Journal of Medicine in 2023 drew wide attention by reporting average body weight reductions of approximately 24 percent at 48 weeks at the highest dose tested. This article explains why researchers added glucagon to the mix, what the trial data shows so far, and where the TRIUMPH phase 3 program stands.

Insulin resistance is the condition in which cells throughout the body respond poorly to insulin, requiring the pancreas to secrete more of the hormone to move glucose out of the bloodstream. It sits at the center of a cluster of related conditions that includes type 2 diabetes, non-alcoholic fatty liver disease, polycystic ovary syndrome, and cardiovascular disease. Understanding what causes it at the cellular level, how it is detected, and what the research shows about reversing or managing it has become one of the more active areas of metabolic medicine over the past two decades.

Testosterone occupies an unusual position in men's health research: it is one of the most widely discussed hormones in clinical medicine, yet its relationship with metabolic disease is more complicated than popular accounts suggest. Low testosterone and metabolic dysfunction tend to travel together, but the direction of causation runs both ways. Excess body fat suppresses testosterone production, and low testosterone facilitates further fat accumulation. Untangling this feedback loop, and determining when testosterone replacement actually helps, has been the focus of several major clinical trials over the past decade.

Sleep has moved from the periphery of metabolic medicine to one of its most studied modifiable variables over the past two decades. A body of research now links short sleep duration, poor sleep quality, and circadian disruption to insulin resistance, weight gain, elevated cortisol, suppressed testosterone, and a cluster of findings that overlap substantially with metabolic syndrome. This article walks through what that research shows, where the evidence is strongest, and what remains an open question.