---
title: "Glossary of peptide research terms"
url: https://humanpeptides.fyi/glossary
site: humanpeptides.fyi
last_reviewed: 2026-10-11
---


# The terms, defined.

## Study types

- **Randomized controlled trial (RCT):** A study that assigns people by chance to the treatment or a comparison (often placebo), so differences in outcome can be attributed to the treatment rather than to who chose it.
- **Placebo-controlled:** A study in which the comparison group receives an inactive look-alike, so that expectation effects are present in both groups.
- **Double-blind:** Neither participants nor investigators know who received the treatment until the study ends, which reduces bias in reporting and assessment.
- **Open-label / unblinded:** Everyone knows who received the treatment. Results are more prone to expectation and reporting bias.
- **Phase 1, 2 and 3 trials:** Phase 1 tests safety and dosing in a small group; phase 2 looks for signs of effect in more people; phase 3 tests effect and safety at scale and usually supports an approval application.
- **Meta-analysis:** A study that statistically combines the results of several earlier studies on the same question.
- **Observational study / cohort:** A study that follows people without assigning a treatment. It can show associations but not cause and effect.
- **Case report:** A description of what happened to one patient or a few patients. Useful for spotting rare effects, not for judging how often they occur.
- **Retrospective study:** A study that looks back at existing records rather than following people forward under a plan.
- **Pilot study:** A small early study meant to test feasibility, not to prove an effect.

## Evidence levels

- **In vitro:** Studied in cells or tissue in a dish or test tube, outside a living organism.
- **Ex vivo:** Studied in tissue taken from a living organism and kept alive outside it, such as isolated hair follicles.
- **In vivo / animal study:** Studied in a living organism, most often mice or rats. Results frequently fail to carry over to humans.
- **Preclinical:** Research done before human testing, in cells and animals.
- **Anecdotal:** A personal report, for example a forum post. Unverified, not controlled, and not evidence that something works or is safe.
- **Evidence label (this site):** One of five labels on every entry: Approved (specific use), Trial-backed, Early human, Preclinical or Unstudied. It summarizes the strongest kind of evidence found, not whether something works.

## Regulation

- **FDA-approved:** The US Food and Drug Administration has approved a specific product for specific uses, doses and patients. Approval does not extend to other uses.
- **Accelerated approval:** An FDA pathway that approves a drug on early evidence for a serious condition, with confirmatory trials required afterward.
- **Off-label:** Use of an approved drug for a purpose, population or dose that its approval does not cover.
- **Compounding:** Preparation of a medication by a pharmacy for an individual patient. Compounded drugs are not FDA-approved and are not reviewed for safety or effectiveness before use.
- **503A and 503B:** Sections of US law covering compounding pharmacies (503A) and outsourcing facilities (503B), including which bulk ingredients they may use.
- **FDA Category 1 and Category 2:** FDA lists for bulk substances nominated for compounding: Category 1 substances are under evaluation; Category 2 substances raise significant safety concerns.
- **PCAC:** The FDA Pharmacy Compounding Advisory Committee. Its votes are advice to the FDA, not decisions.
- **Research use only (RUO):** A seller's label meaning a product is not sold for human use. It is not a statement of safety, purity or legality.
- **WADA Prohibited List:** The World Anti-Doping Agency list of substances banned in competitive sport, which includes many peptide hormones and growth factors.

## Biology

- **Peptide:** A short chain of amino acids. Many hormones and signaling molecules in the body are peptides.
- **GLP-1 receptor agonist:** A drug that mimics the gut hormone GLP-1, which affects insulin release, stomach emptying and appetite.
- **GIP:** A gut hormone that, like GLP-1, affects insulin release. Some weight-loss drugs act on both GIP and GLP-1 receptors.
- **Amylin analogue:** A drug that mimics amylin, a hormone released with insulin that contributes to feeling full.
- **GHRH analogue:** A molecule that mimics growth hormone-releasing hormone, signaling the pituitary gland to release growth hormone.
- **Growth hormone secretagogue:** Any substance that causes growth hormone to be released, including GHRH analogues and ghrelin mimetics.
- **IGF-1:** Insulin-like growth factor 1, a hormone made mainly in the liver in response to growth hormone.
- **Melanocortin receptors:** A family of receptors involved in skin pigmentation, appetite and sexual arousal.
- **Telomere:** The protective cap at the end of a chromosome, which shortens as cells divide.
- **Senescent cell / senolytic:** A senescent cell has stopped dividing but remains active; a senolytic is a substance meant to clear such cells.
- **Mitochondria:** Structures inside cells that produce most of the cell's chemical energy.
- **Half-life:** The time it takes for the amount of a substance in the body to fall by half.
- **Stack / blend:** Two or more compounds taken together (stack) or mixed in one vial (blend). Most stacks and blends have never been studied as combinations.