Informational only. Not medical advice.INFORMATIONAL PLATFORM ONLY — NOT MEDICAL ADVICE, DIAGNOSIS, OR TREATMENT
Informational only. Not medical advice.INFORMATIONAL PLATFORM ONLY — NOT MEDICAL ADVICE, DIAGNOSIS, OR TREATMENT
Head-to-head comparison of Dihexa and P21 — mechanism, side effects, legal status, and pricing.
Dihexa (PNB-0408) is a small-molecule hexapeptide-like analog of angiotensin IV developed at Washington State University by the Harding/Wright group as a preclinical candidate for Alzheimer's disease and cognitive decline. It is NOT FDA-approved and has never been tested in human clinical trials. The often-quoted claim that it is 'roughly ten million times more potent than BDNF' refers to EC50 comparisons in an in vitro dendritic spine assay, not clinical efficacy.
P21 (also P021) is a small peptidergic compound — the tetrapeptide core Asp-Gly-Gly-Leu with an N-terminal acetyl and a C-terminal adamantylated glycine amide (Ac-DGGL(A)G-NH2) — derived from an active region (residues ~148–151) of human ciliary neurotrophic factor (CNTF). It was designed and characterized in the Khalid Iqbal laboratory at the New York State Institute for Basic Research in Developmental Disabilities (NYS IBR). It is an experimental, preclinical compound — NOT FDA-approved and NOT tested in humans in published trials. Distinct from the cyclin-dependent kinase inhibitor protein p21/CDKN1A/WAF1 (a completely different gene product; the two share only the name).
Dihexa
P21
Category
Legal Status
Mechanism
Half-life
Side Effects
COA-verified vendors · trust score ≥70 required · single-vial price — bulk/bundle deals may be lower
Dihexa
P21
COA corpus from Disclosed Labs — independently tested batches only.
Dihexa
4
COAs
99.1%
Avg purity
4
Labs
P21
2
COAs
99.1%
Avg purity
1
Labs
McCoy et al. (J Pharmacol Exp Ther 2013, PMID 23055539) is the original dihexa characterization: oral dihexa reversed scopolamine-induced memory deficits and improved Morris water maze performance in aged rats at low doses. Sun et al. (Brain Sci 2021, PMID 34827486) reported that dihexa rescued cognitive impairment in the APP/PS1 Alzheimer's mouse via PI3K/AKT signaling, with increased synaptophysin and reduced neuroinflammation. Wright & Harding (J Alzheimers Dis 2015, PMID 25649658) reviewed the brain HGF/c-Met system as an Alzheimer's target. Note: Benoist et al. (JPET 2014, PMID 25187433), which reported the HGF/c-Met-dependent synaptogenesis mechanism, was retracted in 2025 and should not be relied on as primary evidence. The 'roughly seven orders of magnitude more potent than BDNF' descriptor refers to in vitro dendritic spine EC50 values, not clinical efficacy. Dihexa has never entered human clinical trials; Athira Pharma's related analog fosgonimeton failed its Phase 2/3 LIFT-AD Alzheimer's endpoint in 2024 and was discontinued, after which Athira shifted focus to ATH-1105 for ALS.
Key references
Evidence is preclinical (rodent) only. Key publication: Kazim, Blanchard, Dai, Tung, LaFerla, Iqbal & Iqbal, Neurobiology of Disease 2014 (PMID 25046994) reported that chronic oral P021 rescued cognition, boosted dentate-gyrus neurogenesis, and reduced tau hyperphosphorylation in 3xTg-AD mice. Additional preclinical papers from the Iqbal group (and collaborators) have shown dendritic/synaptic rescue in AD and aging rodent models (e.g., Kazim et al., Alzheimer's Res Ther 2017). No Phase 1/2/3 human trials have been published; no human safety or pharmacokinetic data exist. Grey-market vendor material is unvalidated — purity, identity, and dosing are not verifiable.
Dihexa and P21 are both in the Cognitive category and may have overlapping mechanisms. Researchers should review both profiles carefully, understand the mechanisms of action, and monitor the relevant biomarkers when combining compounds in the same class. As always, consult a licensed healthcare provider before making any decisions about combining research compounds.
This platform provides informational tools only, not medical advice. This comparison is for educational purposes only. Consult a licensed provider.
Contraindications
Lab Testing
Disclosed Labs