Neurological and Cognitive Research
What human studies show for peptides studied in memory, stroke, dementia, anxiety and autism, including Semax, Selank, Cerebrolysin, a GHRH analog, semaglutide and oxytocin, with limits and negative results.
Content last updated . This page has not been medically reviewed.
Quick answer
Brain and cognition is a topic where many peptides have been tried and several large trials came back negative. The sources checked for this page found no peptide with solid, independently confirmed benefit for memory or thinking in healthy people. Promoted "nootropic" peptides such as Semax and Selank have mostly small studies from Russia, open-label designs, or animal work. Please do not read this page as a recommendation for any product.
Evidence labels used here. Mixed: studies disagree. Promising but limited: small or indirect human data. Preclinical: cells or animals only. No good evidence of benefit: good trials found no difference. Proper evidence not found: we looked and found nothing usable. A blood level such as BDNF (a growth-related protein) is a biomarker. A better score on a daily-living scale, or slower dementia, is a clinical outcome.
For everyday memory and focus, see Focus and Memory, and for warning signs, Memory Changes: When to Get Help. Compound profiles for two promoted peptides are on Semax and Selank.
Evidence by molecule
| Molecule and use | Design, people, size, length | Main result | Funding and limits |
|---|---|---|---|
| Semax, motor neuron disease (2007) | Open-label trial, sequential groups of 27 patients; given through the nose in two 10-day courses [1] | No effect on disease course or clinical scores; quality-of-life score improved, driven by mood and motivation [1] | No placebo group. Open-label. Funder not stated in the abstract read. |
| Semax, after ischemic stroke (2018) | 110 patients, early or late rehabilitation, with or without Semax [2] | Higher blood BDNF and better Barthel score (a daily-living scale) in the Semax groups [2] | Abstract describes subgroups, not blinding. BDNF is a biomarker. Independent replication not found. |
| Selank, anxiety (2008) | 62 patients with generalized anxiety or neurasthenia; Selank (30) versus the benzodiazepine medazepam (32) [3] | Anxiety-lowering effects of both drugs were similar [3] | Active comparator, no placebo. Small. Published in Russian. |
| Cerebrolysin, vascular dementia (Cochrane 2019) | Six randomized trials, 597 people, follow-up 15 days to three years [4] | Small gains on cognitive tests (very low-quality evidence); authors said effects may be too small to matter [4] | All trials with funding details were industry-supported; high risk of bias. [4] |
| Cerebrolysin, acute stroke (Cochrane 2023) | Seven randomized trials, 1,773 people, including one trial of a similar brain-derived mixture [5] | Probably no benefit for preventing death; a possible increase in non-fatal serious adverse events [5] | Manufacturer supported three trials. |
| Tesamorelin (a GHRH analog), older adults and mild cognitive impairment (2012) | Randomized, double-blind, placebo-controlled; 152 adults aged 55 to 87 (66 with MCI); 20 weeks [6] | Better thinking-test composite (p = 0.03 intent-to-treat); IGF-1 up 117% (biomarker); adverse events 68% versus 36% on placebo [6] | Authors called for longer trials. Test scores, not daily function. Funder not stated in the abstract read. |
| Oral semaglutide, early Alzheimer's (2026) | Two double-blind phase 3 trials, 3,808 people with amyloid-confirmed disease; up to 156 weeks [7] | No slowing of dementia progression versus placebo (CDR-SB difference not significant) [7] | Funded by Novo Nordisk. Adverse events 91.2% versus 84.8%. [7] |
| Intranasal oxytocin, autism in children (2021) | 290 children and teens, 24-week placebo-controlled phase 2 trial [8] | No difference in social function measures; adverse events similar [8] | Funded by a US government institute (NICHD). [8] |
What the table says in plain words
- Semax and Selank. The human work found is small, mostly open-label or against another drug, and in Russian-language journals. In animals, a single Semax dose raised BDNF in the rat hippocampus. [9] That is preclinical. Neither is shown to improve memory in healthy adults. Proper evidence not found for large placebo-controlled trials in English-language sources checked. Regulatory status in Russia or elsewhere was not verified here.
- Cerebrolysin is a mixture of small peptides and amino acids from pig brain, not a single defined peptide. [5] Cochrane's reviewers called the supporting evidence for vascular dementia weak. [4]
- Negative results matter. Two industry-funded trials of semaglutide in Alzheimer's disease found no benefit. [7] A government-funded autism trial of oxytocin found none either. [8] A drug being approved for one purpose (semaglutide for diabetes or weight) does not mean it treats another.
- Biomarker versus outcome. The tesamorelin trial raised IGF-1 and improved test scores, but it did not test dementia prevention or daily function. Higher IGF-1 is not automatically better. [6]
Frequently asked questions
Do Semax or Selank improve memory?
The sources checked do not show that. Human data are small, often open-label and published in Russian, and animal findings do not carry over to people. [1][3][9]
Does Cerebrolysin work for stroke or dementia?
Cochrane found probably no benefit on death after stroke and weak evidence for vascular dementia. [5][4]
Did semaglutide slow Alzheimer's disease?
Not in two large phase 3 trials of oral semaglutide, which were stopped for negative outcome. [7]
Is a higher IGF-1 a sign of better brain function?
Not by itself. In the tesamorelin trial IGF-1 rose 117% and test scores improved, but long-term brain outcomes were not shown. [6]
Is intranasal oxytocin proven for autism?
A large placebo-controlled trial in children found no difference. [8]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Regulatory note (United States)
On the FDA page "Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks" (content current as of 04/22/2026, read 2026-10-22), Semax and Selank acetate appear in the section "nominated but withdrawn", described as substances previously in category 2 that were withdrawn by the nominators. [10] The text says compounded Semax and Selank may pose risk for immunogenicity for certain routes. [10] This does not by itself say whether either may be sold or prescribed, and laws change. Not legal advice. See Approved, Investigational and Unapproved Peptides.
Safety and who should talk to a clinician
Memory loss, new confusion, stroke symptoms and severe anxiety need medical evaluation, not a promoted peptide. In the Cerebrolysin stroke review, non-fatal serious adverse events were more frequent with the drug. [5] For product-quality cautions, see Peptide Safety: Adverse Events, Contamination and Injection Risks.
References
- The study of chronic partial denervation and quality of life in patients with motor neuron disease treated with semax (in Russian). Zh Nevrol Psikhiatr Im S S Korsakova 2007. PubMed abstract read 2026-10-22.
- The efficacy of semax in the treatment of patients at different stages of ischemic stroke (in Russian). Zh Nevrol Psikhiatr Im S S Korsakova 2018. PubMed abstract read 2026-10-22.
- Efficacy and possible mechanisms of action of a new peptide anxiolytic selank in the therapy of generalized anxiety disorders and neurasthenia (in Russian). Zh Nevrol Psikhiatr Im S S Korsakova 2008. PubMed abstract read 2026-10-22.
- Cerebrolysin for vascular dementia. Cochrane Database Syst Rev 2019. PubMed abstract read 2026-10-22.
- Cerebrolysin for acute ischaemic stroke. Cochrane Database Syst Rev 2023. PubMed abstract read 2026-10-22.
- Baker LD et al. Effects of growth hormone-releasing hormone on cognitive function in adults with mild cognitive impairment and healthy older adults: results of a controlled trial. Arch Neurol 2012. PubMed abstract read 2026-10-22.
- Efficacy and safety of oral semaglutide 14 mg (flexible dose) in early-stage symptomatic Alzheimer's disease (evoke and evoke+): two phase 3, randomised, placebo-controlled trials. Lancet 2026. PubMed abstract read 2026-10-22.
- Intranasal Oxytocin in Children and Adolescents with Autism Spectrum Disorder. N Engl J Med 2021. PubMed abstract read 2026-10-22.
- Semax, an analog of ACTH(4-10) with cognitive effects, regulates BDNF and trkB expression in the rat hippocampus. Brain Res 2006. PubMed abstract read 2026-10-22.
- FDA, Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (page content current as of 04/22/2026). Read 2026-10-22.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.