Why animal results so often stall
A mouse is a serious experimental system. It is not a small human.
The translation problem
Most candidates that look promising in cells or rodents never become a useful human medicine. Species differ in receptors, metabolism, immune response, and the disease itself. A tendon healed in a rat under a controlled wound is not a person with a year-old injury and three other diagnoses.
Dose does not scale by body weight in any simple way. A milligram per kilogram in a mouse can be a completely different exposure once human clearance, protein binding, and route are different. Half-lives do not transfer. If this index does not list a human half-life, it is because one was not verified here, not because the animal number was “close enough.”
What preclinical work is for
Cell and animal studies are how a mechanism gets a chance to be wrong early. They can show that a peptide binds a receptor, moves a pathway, or changes a tissue in that model. That is worth knowing. It is the start of a hypothesis.
BPC-157 is the cautionary shape. There is a large animal literature and, as of a 2026 systematic review whose search ended 1 June 2026, three small uncontrolled human studies and very low certainty. The animal work did not fail to exist. It failed to answer the human question.
Sources for the named trials and approvals live on the compound pages and in the evidence explorer. This essay does not add new numbers.