The terms, defined.

Plain-language definitions of the 38 research, regulatory and biology terms used across this index, from RCT and preclinical to 503A and GLP-1. Definitions describe terms only; they make no claim about any compound.

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.