Four kinds of evidence. Only one of them is proof.

Almost every argument you will ever read about a peptide rests on one of four kinds of evidence. They are not equal, and most of the noise in this space comes from treating them as if they were.

The first is human data. This is what actually happened when real people took the compound. Randomized controlled trials sit at the top, because they separate the effect of the compound from everything else. Human data is the only category that constitutes proof. The second is animal data, studies in mice, rats, or cells. Useful, because they generate the hypotheses that human trials test, but a starting point, not a conclusion. Most striking rodent results never reproduce in humans.

The third is mechanism, the sentence that begins, it activates pathway X. Mechanism describes how a compound could work. It is plausibility, not outcome, and it is the most abused category because it sounds rigorous. A clean mechanistic story can make a compound with zero human evidence feel proven. The fourth is marketing, a claim with no tier at all, repeated until it feels true. It is the default state of the peptide internet.

Hold these four in order and every claim sorts itself. Is this human data, animal data, mechanism, or marketing? That one question is the entire discipline. It is the lens behind every grade Peptide Pressure publishes.