AOD-9604

AOD-9604 was developed in the 1990s from research seeking to separate the metabolic activity of human growth hormone from its broader growth-promoting effects. It is a modified analog of the hormone’s C-terminal region, commonly described as Tyr-hGH 177–191 rather than an exact copy of naturally occurring hGH fragment 176–191.¹ Early rodent and adipose-tissue studies examined whether this smaller sequence could influence lipid metabolism without substantially increasing IGF-1 or reproducing the full endocrine profile of growth hormone. Investigators reported increased fat oxidation, lipolytic activity and reduced fat accumulation in several preclinical models.¹–⁴ These findings led to clinical development for obesity. AOD-9604 progressed through human studies, but later trials did not demonstrate consistent, clinically meaningful weight-loss effects, and the development program was discontinued.⁵ ⁶ Research subsequently expanded into cartilage and connective-tissue models. AOD-9604 is historically notable because it advanced further in clinical testing than many experimental peptide fragments. Its human weight-loss program, however, did not validate the efficacy suggested by early animal studies.

AOD-9604 has been studied primarily for effects on lipid handling in adipose tissue, but its initiating receptor and complete molecular pathway have not been identified. Preclinical studies reported increased breakdown of stored triglycerides and reduced formation or accumulation of new lipid under certain experimental conditions.⁷ ⁸ Some work proposed involvement of hormone-sensitive lipase and increased lipid oxidation, but these findings do not establish one confirmed receptor-level mechanism. Unlike full-length growth hormone, AOD-9604 was designed to avoid substantial activation of the GH–IGF-1 axis. Experimental studies generally did not show the same increase in IGF-1 or broad growth-related signaling associated with growth hormone.⁷ This distinction is central to its research design, although it should not be interpreted as proof of clinical effectiveness or safety. A separate preclinical literature has examined cartilage turnover, including changes in proteoglycan and collagen-related processes in osteoarthritis models.⁹ Most mechanistic evidence remains animal or cell based, and human weight-loss studies have been inconsistent. The exact molecular target remains unresolved.