Dihexa

Dihexa is a lab-derived, peptide-like compound marketed online as a potent BDNF-mimetic nootropic — and the honest story is unusually clear-cut even by this site's D-grade standards. The company that originally held its development rights, later renamed Athira Pharma, concluded it had poor drug-like properties and never took it into human testing at all. It instead developed a related but distinct prodrug, fosgonimeton, which did reach real human trials — and that compound has since missed its primary endpoints in both an Alzheimer's disease trial (LIFT-AD, 2024) and a Parkinson's disease dementia trial (SHAPE, 2023). Even the closest thing to a human test of this mechanism came back negative.

What it is

Dihexa is a small, peptide-derived compound developed from angiotensin IV research at Washington State University, targeting the hepatocyte growth factor (HGF)/c-Met receptor system rather than a classical growth-hormone-secretagogue or direct BDNF-receptor pathway. In rodent studies, it showed effects on synaptogenesis and cognitive performance measures at very low doses — the basis for marketing claims that it is many orders of magnitude more potent than BDNF itself, a claim that traces to in-vitro synaptogenesis-assay comparisons, not a demonstrated human cognitive effect at any dose.

Why it was never tested in humans

The company originally formed to commercialize dihexa, M3 Biotechnology, evaluated more than 50 related HGF/c-Met-pathway compounds and concluded dihexa itself had inadequate solubility and pharmacokinetic properties for human drug development. It shifted its lead program to a different, related compound — fosgonimeton — which the company (renamed Athira Pharma in 2019) states is metabolized in the body to an active form related to, but distinct from, dihexa itself. As a direct result, dihexa itself has no completed or currently registered human clinical trial.

Its closest human-tested relative failed too

Fosgonimeton reached real human trials: a Phase 1 safety/PK study, and Phase 2/3 efficacy trials LIFT-AD (mild-to-moderate Alzheimer's disease) and SHAPE (Parkinson's disease dementia and dementia with Lewy bodies). LIFT-AD (topline results announced September 2024) did not meet its primary Global Statistical Test endpoint (-0.08 change favoring drug, p=0.70) nor key secondary endpoints (ADAS-Cog11, ADCS-ADL23) over 26 weeks, though pre-specified subgroups (moderate AD, APOE4 carriers) showed some cognitive stabilization. SHAPE (results December 2023; enrollment ended early at 28 of a planned 75 subjects due to design limitations) also missed its primary endpoint by protocol-specified analysis, though it showed a statistically significant difference on one measure (ADAS-Cog13) and was well tolerated.

What's actually sold online

The "dihexa" sold as an injectable or oral nootropic online is an unregulated research chemical with no approved status, no established human safety data, and — per the company that actually held its original development rights — was never advanced to human testing because of the compound's own perceived shortcomings. Combined with its closest tested relative's two clinical misses, the evidence gap here is about as wide and well-documented as any D-grade entry on this site.