The Peptides Facts Research Desk

The research desk compiles evidence summaries from primary literature, with an emphasis on separating what has been demonstrated in humans from what has been demonstrated in animal models or in vitro.

20 articles

• Selank: Proposed Anxiolytic Mechanism and the State of the Evidence

  Selank is a tuftsin analogue registered as an anxiolytic in Russia and nowhere else. Its proposed mechanism is indirect modulation of GABAergic signalling, and the literature supporting it is real, substantial and genuinely difficult to appraise from outside.

• Reading a Peptide Sequence: Direction, Codes, Fragments and Modifications

  A peptide sequence is a specification; a peptide name usually is not. The conventions that make a sequence readable — direction, numbering, two symbol sets, fragment ranges and modification notation — are few, fixed, and worth learning once.

• L-Carnitine Is Not a Peptide: What It Does and What the Evidence Supports

  Carnitine is a single small molecule of about 161 daltons that sits in peptide catalogues for commercial reasons rather than chemical ones. Its role in fatty acid transport is textbook biochemistry; the fat-loss claim built on top of that role is a separate question with a much weaker answer.

• HCG: A Real Hormone Attached to a Refuted Diet Claim

  Human chorionic gonadotropin has a defined receptor, a well-described mechanism and approved clinical uses in fertility and male endocrinology. It also carries one of the most thoroughly disproved claims in the history of obesity treatment, and the first fact is why the second one lasted.

• Why Most Peptides Are Not Orally Bioavailable

  The gastrointestinal tract is a protein-digestion system, and a swallowed peptide is its intended substrate rather than an unlucky bystander. Five barriers stand between the mouth and the circulation, and unmodified peptides clear all five at well under 1%.

• Peptide Half-Life: Why Clearance Is So Fast, and the Five Ways It Is Slowed

  Two independent systems remove peptides from circulation — peptidases cut them and the kidney filters them — and both work quickly. Extending half-life means defeating both, and every method of doing so has a price.

• Growth Hormone in Healthy Older Adults: One Study, and What Came After It

  A 1990 report on twelve men over 60 is still the foundation of growth hormone's anti-aging reputation. The randomised trials that followed found something considerably smaller, alongside a list of harms.

• PT-141 (Bremelanotide): Melanocortin Pharmacology and the Development Story

  A metabolite of Melanotan II that took the other road: randomised trials, a formulation abandoned over a blood pressure signal, and an approval. The mechanism is central, and the effect size is modest.

• Retatrutide: Triple Glucagon, GIP and GLP-1 Receptor Agonism, and the Balance It Has to Strike

  Retatrutide adds a glucagon receptor arm to the two incretin receptors tirzepatide already engages. Glucagon raises blood glucose, which makes that the most counterintuitive design decision in the class — and the reason the molecule acts on energy expenditure as well as intake.

• Melanotan II: The Documented Safety Signals

  A non-selective melanocortin receptor agonist that was never developed as a medicine. What the case-report literature records, and why the absence of controlled safety data is itself the central finding.

• Epitalon and Telomerase: An Assessment of the Evidence Base

  The claims made for epitalon are specific, mechanistic and testable. The evidence behind them is small, concentrated in a single research programme, and largely unreplicated. That combination is the finding.

• MOTS-c: A Peptide Written by the Mitochondrial Genome, and the AMPK Mechanism Proposed For It

  MOTS-c is a 16-amino-acid peptide encoded inside the mitochondrial genome rather than the nuclear one. That single fact makes it a different kind of molecule from almost every other peptide discussed in this field, and it shapes the mechanism proposed for it.

• CJC-1295, the Drug Affinity Complex, and the Half-Life That Defines It

  CJC-1295 with DAC and "CJC-1295 without DAC" are not two versions of one compound. They are different molecules whose half-lives differ by orders of magnitude, and only one of them is what the published literature calls CJC-1295.

• Tirzepatide: Dual GIP and GLP-1 Receptor Agonism, and Why the Balance Is Uneven

  Tirzepatide engages two incretin receptors instead of one, and it does not engage them equally. The receptor-level asymmetry is the most interesting thing about the molecule, and the part of it that is least settled.

• Peptide or Protein: Where the Boundary Sits, and Who Decides

  Chemically the two are the same class of molecule. The line between them is drawn by convention, by folding behaviour, by how the molecule is manufactured — and, in the United States, at exactly 40 residues by statute.

• AOD9604: A Compound That Worked in Mice and Failed in People

  The rodent data were strong, the mechanism was coherent, and the human trials did not replicate it. AOD9604 is the most instructive failure in the peptide literature, and it is rarely described as one.

• Semaglutide: The GLP-1 Receptor, and Three Modifications That Made a Weekly Drug

  Native GLP-1 survives about two minutes in circulation. Semaglutide survives about a week. The engineering that produced that difference is the clearest worked example of peptide drug design in the literature.

• GHK-Cu: How a Three-Residue Peptide Carries Copper, and What That Explains

  Glycyl-histidyl-lysine binds copper(II) with unusually high affinity. Most of the compound's reported activity is attributed to that single property — and most of its literature comes from one research group.

• TB-500 and Thymosin β4: The Mechanism, and Why the Two Are Not Interchangeable

  Thymosin β4 is a 43-residue actin-sequestering peptide with a well-characterised cellular function. TB-500 is a shorter synthetic construct sold under its name. Conflating them distorts most of what is written about both.

• BPC-157: What the Evidence Says About Its Mechanism of Action

  A pentadecapeptide derived from a gastric protein, studied largely in rodent models. Here is what is actually established about how it behaves, and where the evidence stops.