Evidence-Based Summary
Dihexa and Semax are both sold online as cognitive enhancers, but their evidence is very different. Dihexa is a modified fragment of angiotensin IV developed at Washington State University. All published evidence comes from animals and cells. The 2014 paper proposing that it works through the HGF/c-Met growth-factor system was retracted in 2025, and the original 2013 dihexa paper carries a 2021 expression of concern. FDA says it has found no human exposure data for dihexa by any route. Semax is a heptapeptide based on a fragment of ACTH, studied and used clinically in Russia. Its human evidence consists of small, non-randomized Russian stroke studies and brain-imaging studies in healthy volunteers. No study has compared the two, neither is FDA-approved, and FDA lists both as compounding substances that may present significant safety risks.
Quick Comparison: Dihexa vs Semax
A high-level comparison of molecule class, molecular receptor targets, FDA regulatory approvals, and verified clinical programs.
| Feature | Dihexa | Semax |
|---|---|---|
| Class | Small modified angiotensin IV fragment (hexanoyl-Tyr-Ile-aminohexanoic amide) | Heptapeptide: ACTH(4-7) fragment plus Pro-Gly-Pro (Met-Glu-His-Phe-Pro-Gly-Pro) |
| Proposed target | HGF/c-Met system (the key paper was retracted in 2025) | BDNF/TrkB signaling in rat brain; no single receptor established |
| How it has been given in studies | Reported as orally active in rat studies by its developers; no human use studied | Intranasal in human studies |
| U.S. regulatory status | Not FDA-approved; on FDA's compounding safety list (dihexa acetate) | Not FDA-approved; on FDA's compounding safety list (semax heptapeptide) |
| Strongest human evidence | None: no published human studies | Small non-randomized Russian stroke studies; fMRI studies in healthy volunteers |
| Research integrity notes | Mechanism paper retracted (2025); original paper under expression of concern (2021) | Most studies come from developer-linked Russian groups |
| Main safety concerns | FDA: no human exposure data by any route | FDA: immunogenicity, impurities, limited safety information |
| WADA status (2026) | Not named; WADA's S0 class covers substances with no government approval for human use | Not named on the 2026 Prohibited List |
A Retracted Growth-Factor Hypothesis vs Neurotrophin Findings in Rats
Both compounds are linked to brain growth factors, but these links come from animal and cell studies. For dihexa, the central mechanism paper no longer stands.
Dihexa
Primary Target: Proposed HGF/c-Met system (unconfirmed)
Affinity Profile: Reported by developers; supporting paper retracted
The developers reported that dihexa was orally active, crossed the blood-brain barrier and reversed memory deficits in scopolamine-treated and aged rats (2013; expression of concern 2021). Their 2014 paper tying this to HGF/c-Met signaling was retracted in 2025. An independent mouse study reported benefits, while a rat Huntington's-like model found none.
Semax
Primary Targets: No single receptor established
Affinity Profile: Raises BDNF and TrkB activity in rat hippocampus
In rats, a single administration increased BDNF protein and TrkB activation in the hippocampus and improved a learning task. It also slowed enkephalin breakdown in human serum samples. A Russian stroke study reported higher blood BDNF in treated patients, but that study was not randomized.
FDA, International and Anti-Doping Status
United States status checked 11 October 2026. FDA's significant-safety-risk compounding list (content current as of 22 April 2026) names both dihexa acetate and semax (heptapeptide).
Dihexa Status & Formulations
No FDA-approved medicine contains dihexa, and it is not approved anywhere that we found. FDA states it has not identified any human exposure data for dihexa acetate by any route and lacks information on whether it would harm people. Fosgonimeton, a related phosphate prodrug, is a separate investigational compound whose Phase 2/3 Alzheimer's trial missed its primary and secondary endpoints. Not named on WADA's 2026 list; the S0 class covers substances with no government approval for human therapeutic use.
Semax Status & Formulations
Not FDA-approved or EMA-approved. FDA lists semax among bulk drug substances that may present significant safety risks, citing immunogenicity and impurity concerns and no or limited safety information for proposed routes. It is studied and used clinically in Russia; this page did not independently verify its current Russian registration. No ClinicalTrials.gov record was found. Not named on WADA's 2026 Prohibited List.
Critical Regulatory Distinction
Clinical use in Russia is not U.S. approval, and fosgonimeton's trial results do not apply directly to dihexa. A 2020 Belgian analysis found Semax in unlabelled seized preparations sold online.
No Human Data vs Small Russian Studies
This comparison sets a compound with no published human studies against one with small, mostly non-randomized human studies. Neither has evidence that it improves memory in healthy people.
Dihexa: Clinical Evidence Overview
No published human study of dihexa was found. FDA states it has found no human exposure data for any route. The closest human data come from fosgonimeton, a related company-developed compound: in the LIFT-AD Phase 2/3 trial (primary analysis of 287 people with mild-to-moderate Alzheimer's disease), it did not significantly improve cognition or daily function versus placebo, and more participants stopped because of side effects, mainly injection-site reactions. Those results describe fosgonimeton, not dihexa.
Semax: Clinical Evidence Overview
A 1997 controlled study added Semax to standard care in 30 acute stroke patients, compared with 80 conventionally treated patients, and reported somewhat faster recovery of neurological function. A 2018 study of 110 stroke-rehabilitation patients reported higher blood BDNF and better Barthel scores with Semax, but patients were not randomized. Brain-imaging studies in healthy volunteers (24 and 52 participants) found changes in resting brain networks, without testing memory or thinking.
Curated Clinical Evidence Table
A curated selection of the primary studies behind each compound’s evidence profile. Results from different studies are not directly comparable.
| Study & Citation | Population | Comparison & Dosing | Duration | Main Endpoint | Key Finding | Methodological Limitations |
|---|---|---|---|---|---|---|
| McCoy et al., 2013 (dihexa) | Scopolamine-treated and aged rats | Dihexa and related angiotensin IV analogues | Short-term experiments | Water maze performance, synapse formation | Developers reported reversal of memory deficits and more synapses. | Animal study; journal expression of concern (2021). |
| Benoist et al., 2014 (dihexa) | Rats and cultured neurons | Angiotensin IV analogues with HGF/c-Met blockade | Experimental | Proposed HGF/c-Met mechanism | Retracted in 2025; findings should not be relied on. | Retracted. |
| Wells et al., 2024 (dihexa) | Rats, Huntington's-like model | Dihexa vs control | Experimental | Weight, motor and memory measures | No protection found. | Animal model; negative result. |
| Gusev et al., 1997 (Semax) | 30 acute stroke patients vs 80 controls | Semax added to standard care vs standard care | Acute treatment course | Neurological recovery scales, EEG | Reported somewhat faster recovery of motor and general deficits. | Not randomized or blinded; Russian-language; developer co-author. |
| Gusev et al., 2018 (Semax) | 110 stroke-rehabilitation patients | With vs without Semax, early vs late rehabilitation | About 5 months | Blood BDNF, motor strength, Barthel index | Higher BDNF and better Barthel scores with Semax. | Not randomized; Russian-language. |
| Lebedeva et al., 2018 (Semax) | 24 healthy volunteers | Intranasal Semax vs placebo | Single administration | Resting-state brain network (fMRI) | Larger frontal default-mode network component with Semax. | Imaging change only; no cognitive outcome. |
What Is Known About Safety
Dihexa has no human safety data at all. Semax has only small human studies. FDA lists both as compounding substances that may present significant safety risks.
Unknown human safety for dihexa
FDA says it has not identified any human exposure data for dihexa acetate by any route, so the agency cannot judge whether it would harm people.
| Safety Consideration | Dihexa | Semax |
|---|---|---|
| Human safety data | None published | Small Russian clinical studies |
| FDA concern | No human exposure data by any route | Immunogenicity, impurities, limited safety information |
| Research integrity | Retracted mechanism paper; expression of concern on original paper | No retractions identified; evidence concentrated in developer-linked groups |
| Product quality | Unregulated online products of unknown purity | Unregulated online products; found unlabelled in seized samples |
What Dihexa and Semax Have in Common
Where the two compounds overlap in biology, evidence or regulatory context.
Marketed for cognition
Both are promoted online as memory or focus enhancers without evidence of benefit in healthy people.
Growth-factor hypotheses
Both are linked to brain growth factors (HGF for dihexa, BDNF for Semax) mainly through animal work.
Same U.S. status
Neither is FDA-approved; both are on FDA's compounding safety list.
Key Scientific & Clinical Differences
Meaningful distinctions in mechanism, strength of evidence, safety and regulatory status.
Human data
Semax has small human studies; dihexa has none.
Research integrity
Dihexa's key mechanism paper was retracted in 2025 and its original paper carries an expression of concern.
Clinical use
Semax is used clinically in Russia, mainly in stroke. Dihexa has never been used as a medicine.
Scientific Comparison vs Clinical Recommendations
Inside Peptides compares scientific evidence, receptor pharmacology, and official regulatory documents to advance public and professional understanding. We do not determine which compound is appropriate for an individual patient, rank medications with arbitrary scores, or recommend initiating or switching treatments.
Decisions about any medicine require a licensed healthcare professional who can weigh personal medical history, contraindications, interactions and monitoring needs. Unapproved peptides have no established safe use, and products sold as “research chemicals” are not the preparations studied in clinical research.
Approved Uses vs Online Claims
A critical scientific distinction between verified, FDA-approved clinical uses and unverified claims circulating on social media and vendor platforms.
Dihexa is millions of times more potent than BDNF at building brain connections
Not supportedFDA has found no human exposure data for dihexa.
We found no peer-reviewed evidence in people for claims like this. The developers' paper proposing its growth-factor mechanism was retracted in 2025, and no human studies have been published.
Semax boosts memory and focus in healthy people
UnprovenNot FDA-approved; on FDA's compounding safety list.
Human studies in healthy volunteers measured brain-imaging changes, not memory or attention. Clinical studies were in stroke patients and were not randomized.
Evidence Strength Across Clinical Domains
Inside Peptides evaluates scientific certainty at the claim level. Because clinical evidence varies significantly depending on the therapeutic endpoint evaluated, each domain is assessed independently.
Cognition in healthy people
Neither has a trial of memory or thinking in healthy people.
Neurological disease
Dihexa has mixed animal results; Semax has small non-randomized stroke studies.
Mechanism
Dihexa's main mechanism paper was retracted; Semax's BDNF findings are from rats.
What Research Still Doesn’t Tell Us
Identifying open scientific questions, pending active-comparator trials, and areas where long-term clinical data remain incomplete.
No human dihexa data
Basic human safety and pharmacology studies of dihexa have not been published.
No randomized Semax trials in Western settings
Semax's stroke evidence needs randomized, blinded, independent trials.
No direct comparison
Dihexa and Semax have never been compared in any study.
Related Compound Profiles
Individual profiles provide full molecular datasheets, CAS numbers, preclinical histories, and compound monographs.
Related Educational Resources
Scientific & Regulatory References
Every pharmacological mechanism, clinical trial result, and regulatory approval cited on this page is traceable to official FDA prescribing documentation, ClinicalTrials.gov registries, or peer-reviewed medical publications.
-
Animal research (expression of concern 2021)
Evaluation of metabolically stabilized angiotensin IV analogs as procognitive/antidementia agents.The journal issued an expression of concern in 2021 (PMID 34551989).
-
Expression of concern
Notice of Concern: McCoy AT, Benoist CC, Wright JW, Kawas LH, Bule-Ghogare JM, Zhu M, Appleyard SM, Wayman GA, and Harding JW (2013) Evaluation of Metabolically Stabilized Angiotensin IV Analogs as Procognitive/Antidementia Agents, J Pharmacol Exp Ther, 344: 141-154; DOI: https://doi.org/10.1124/jpet.112.199497.
-
Retracted animal and cell research
The procognitive and synaptogenic effects of angiotensin IV-derived peptides are dependent on activation of the hepatocyte growth factor/c-met system.Retracted in 2025 (retraction notice PMID 40312093).
-
Retraction notice
Retraction notice to "The Procognitive and Synaptogenic Effects of Angiotensin IV-Derived Peptides Are Dependent on Activation of the Hepatocyte Growth Factor/c-Met System" [J Pharmacol Exp Ther 351 (2014) 390-402].
-
Animal research (mice)
AngIV-Analog Dihexa Rescues Cognitive Impairment and Recovers Memory in the APP/PS1 Mouse via the PI3K/AKT Signaling Pathway.
-
Animal research (rats, negative)
Effects of an Angiotensin IV Analog on 3-Nitropropionic Acid-Induced Huntington's Disease-Like Symptoms in Rats.
-
Phase 2/3 trial of a related compound (company-sponsored)
Fosgonimeton in mild-to-moderate Alzheimer's disease.Tested fosgonimeton, not dihexa; see the trial registry record in References.
-
Trial registry record (fosgonimeton, not dihexa)
ATH-1017 for Treatment of Mild to Moderate Alzheimer's DiseaseCompleted; 554 enrolled (actual). Checked 11 October 2026.
-
Controlled clinical study (Russian-language)
[Effectiveness of semax in acute period of hemispheric ischemic stroke (a clinical and electrophysiological study)].
-
Non-randomized clinical study (Russian-language)
[The efficacy of semax in the tretament of patients at different stages of ischemic stroke].Title spelling ('tretament') as indexed in PubMed.
-
Animal study (rats)
Semax, an analog of ACTH(4-10) with cognitive effects, regulates BDNF and trkB expression in the rat hippocampus.
-
Human imaging study (healthy volunteers)
Effects of Semax on the Default Mode Network of the Brain.
-
Human imaging study (healthy volunteers)
Functional Connectomic Approach to Studying Selank and Semax Effects.
-
Human serum enzyme study
[Semax and selank inhibit the enkephalin-degrading enzymes from human serum]].
-
Analytical study of seized products
The occurrence of putative cognitive enhancing research peptides in seized pharmaceutical preparations: An incentive for controlling agencies to prepare for future encounters of the kind.
-
FDA compounding safety list
Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety RisksPage content current as of 22 April 2026; checked 11 October 2026.
-
Anti-doping rule
World Anti-Doping Code International Standard: Prohibited List 2026