Cognition and anxiety

What human evidence and regulatory status actually support.

The evidence is uneven. It includes small regional clinical studies, preclinical work and a retracted paper. It does not support a general “nootropic stack.” The stroke evidence for Cerebrolysin also leaves a possible serious adverse-event signal unresolved.

Source-based editorial review; independent clinical review pending. Read the sources.

Evidence by peptide

• Selank: Selank is an experimental synthetic peptide. The often-cited anxiety study included 62 people: 30 received Selank and 32 received medazepam. There was no placebo group. The abstract gives broad comparative findings but does not include the symptom percentages or effect sizes that the site previously reported. [1,2]
• Semax: Semax has been studied in Russia and other regional settings, including neurologic indications. Those studies do not establish an FDA-approved cognitive enhancer, a routine wellness dose, or a consumer stacking plan in the United States. [1,2]
• Dihexa: Dihexa is experimental. In April 2025, the journal retracted the 2014 paper behind the HGF/c-Met and cognition claims. That includes the often-repeated line that Dihexa is “10 million times more potent than BDNF.” The retracted paper cannot support those claims. [1,2]
• Cerebrolysin: Cerebrolysin is a porcine-brain-derived peptide mixture used in some countries, but it is not FDA-approved in the United States. A 2023 Cochrane review of acute ischemic stroke found no mortality benefit, no usable functional-outcome evidence, and a possible increase in nonfatal serious adverse events. [1,2]

Common Questions

• Does this page recommend a dose or stack?

  No. Trial protocols describe research, and approved-product instructions apply only to the named formulation and labeled population.

• Can animal, cell or mechanistic findings prove a human benefit?

  No. They can justify further research but cannot be rewritten as a demonstrated outcome in people.

Sources and study limits

1. Optimization of the treatment of anxiety disorders with Selank Medvedev VE, et al. (2008)
2. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks: Selank U.S. Food and Drug Administration
3. Effectiveness of Semax in acute hemispheric ischemic stroke: a clinical and electrophysiological study Gusev EI, et al. (1997)
4. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks: Semax U.S. Food and Drug Administration
5. Retraction: The procognitive and synaptogenic effects of angiotensin IV-derived peptides are dependent on activation of the HGF/c-Met system American Society for Pharmacology and Experimental Therapeutics (2025)
6. The procognitive and synaptogenic effects of angiotensin IV-derived peptides are dependent on activation of the hepatocyte growth factor/c-Met system (retracted) Benoist CC, et al. (2014)
7. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks: Dihexa U.S. Food and Drug Administration
8. Cerebrolysin for acute ischaemic stroke Ziganshina LE, et al. (2023)
9. Unapproved Drugs U.S. Food and Drug Administration

Related Comparisons

• Selank vs Semax: Two distinct experimental peptides with limited, non-interchangeable evidence.

← Browse all peptides

Educational evidence summary. FDA approval, investigational status, and compounding are separate categories. Use the current label and a licensed clinician for patient-specific decisions.

vialprep research · Sources: PubMed, FDA, peer-reviewed trials · How we verify