AOD-9604What the studies show

In the animal work, the fragment did what the full hormone does to fat and little else. In a 2001 study in the International Journal of Obesity, obese mice given AOD-9604 daily for two weeks ate the same amount as controls but gained less weight, burned more fat and had more of the beta-3 adrenergic receptor — the switch on fat cells that triggers fat breakdown — in their fat tissue ³. A companion study in Endocrinology the same year used mice lacking that receptor to probe the mechanism ⁴. Unlike growth hormone, the fragment did not raise blood sugar or IGF-1, and it did not make the mice grow ³. Those animal results were consistent across the Monash group's papers and are not in dispute; the question was always whether they would carry into people.

This is where the story turns. Metabolic Pharmaceuticals ran six clinical trials of AOD-9604 in people, enrolling 925 participants in total, most of them with obesity, with the longest running 24 weeks; in the later trials the compound was given by mouth as a tablet ². Shorter, earlier trials produced small differences from placebo that the company reported in press releases. The larger 24-week study did not: weight loss on AOD-9604 was not significantly different from placebo, and in 2007 the company stopped developing it for obesity ².

The efficacy results were never published in a peer-reviewed journal. What was published, in 2013, is a safety summary of all six trials, which reported no difference from placebo in adverse events and no effect on blood sugar or IGF-1 — the same features that made it look attractive in mice, but with no weight loss to go with them ².

Since the obesity programme ended, the fragment has been studied in animals for joint injury. A 2015 study injected it into the knees of rabbits with experimentally induced osteoarthritis, with and without hyaluronic acid, and reported better cartilage scores than hyaluronic acid alone ⁵. That is one rabbit study, and it is the basis of most of what is now said about AOD-9604 and joints.

AOD-9604 is not an approved drug anywhere. The U.S. FDA has placed it in the category of compounding substances that "may present significant safety risks", the same category as BPC-157, on the grounds that the human data do not establish its effects — a judgement about missing evidence rather than a finding of harm ⁶.

The honest summary is unusual for a research compound: the human data exist, they are the largest body of evidence on it, and they show a tolerable molecule that did not do the thing it was designed to do. The mouse results are real; they did not carry over.