Evidence tier

Not all evidence is equal, and an evidence tier is a quick way to say how much weight a claim can actually bear. It ranks the source of a finding from strongest to weakest, so “studies show” doesn’t get to mean the same thing whether it came from a large human trial or a single cell in a dish.

A rough ladder, strongest at the top:

• Human RCT — randomized controlled trials in people, the gold standard for showing something truly works.
• Human observational — studies that watch groups of people without randomizing; suggestive, but can’t fully prove cause.
• Animal-only — tested in mice or rats but not yet in humans. Promising, not proof.
• In-vitro — done in cells or a test tube, one step further from a living body.
• Anecdotal — individual reports and personal experience. Real signal sometimes, but the weakest rung.

We put an evidence-tier badge on every substance page for a blunt reason: a lot of exciting peptide claims live at the animal or in-vitro level, and it would be dishonest to present them as human-proven. The tier lets you keep the enthusiasm and keep your bearings — you can be hopeful about a compound while knowing exactly how far the proof has actually traveled.

Take semaglutide: its weight-loss evidence belongs in the human-RCT tier because STEP 1 was a randomized, double-blind trial in 1,961 adults, not an animal experiment or a collection of personal reports. Participants received semaglutide or placebo for 68 weeks, giving researchers a direct comparison on prespecified clinical trial endpoints. The trial record reports efficacy and safety outcomes separately, which matters because an evidence tier grades a particular claim, not a molecule as a whole. That tier applies to the claim the trial tested; it does not automatically promote every other claim about semaglutide to the same rung.