Peptides for Cognitive Function: What's Actually Studied

Key takeaways

• No peptide has been shown to improve thinking in healthy adults. The best evidence for any benefit is one 20-week trial of tesamorelin, an FDA-approved growth-hormone-releasing peptide, in 152 older adults: a modest gain in executive function, never replicated.
• The peptides tested most rigorously for memory failed. Intranasal insulin for a year did not help mild cognitive impairment or early Alzheimer's disease, and oral semaglutide did not slow early Alzheimer's disease in two trials of 3,808 people.
• Cerebrolysin, a pig-brain peptide mixture given by infusion abroad, has many small trials; a Cochrane review rated its benefit in vascular dementia very low quality and possibly too small to matter. It is not FDA-approved.
• Semax and Selank, the peptides sold as nootropics, have Russian data in stroke and anxiety and no controlled trial for focus or memory in healthy people. Dihexa has rat data only, and its key papers carry an expression of concern and a retraction.
• For memory loss, attention problems or anxiety, see a clinician: several causes are treatable, and dementia, ADHD and anxiety disorders all have approved treatments.

The direct answer: the peptides that have been properly tested for cognition mostly did not work, and the peptides sold for cognition mostly have not been properly tested. One exception sits in between: tesamorelin, an approved drug, improved executive function modestly in one trial of older adults. Our Semax and Selank hub covers the two best-known nootropic peptides in depth, and our Semax versus Selank comparison answers which is which. This page ranks everything with cognitive data, by how strong that data is.

How we ranked

We ranked by the strength of the human evidence that a peptide improves cognition, using our editorial grades (A for adequate randomized trials, down to D for animal data or none), then by whether a US clinician can legally prescribe it. A large, well-run trial that found no benefit is strong evidence too, so those peptides get their own section rather than a place in the ranking.

The ranking at a glance

1. Tesamorelin: one real trial, small effect

Tesamorelin is a stabilized analog of growth-hormone-releasing hormone, approved in the US as Egrifta for abdominal fat in people with HIV. In the only dedicated cognition trial, 152 adults aged 55 to 87 (66 with mild cognitive impairment) injected tesamorelin 1 mg or placebo at bedtime for 20 weeks. Overall cognition favored tesamorelin (P=.03), driven by executive function (P=.005), with a trend in verbal memory (P=.08); the effect was similar in people with and without mild cognitive impairment. IGF-1 rose 117 percent and body fat fell 7.4 percent, fasting insulin rose 35 percent in the impairment group, and mild side effects were reported by 68 percent on tesamorelin versus 36 percent on placebo (Baker 2012).

That is a genuine randomized, placebo-controlled result, and it is one trial of 20 weeks, never repeated in the same population; a later trial in people with HIV found no clear cognitive benefit, as our tesamorelin profile details. Using tesamorelin for cognition is off-label, and it is not a treatment for dementia. If a clinician prescribes it for any reason, the dose on the pharmacy label governs; the reconstitution calculator only checks the arithmetic of a dispensed vial.

2. Cerebrolysin: many trials, weak ones

Cerebrolysin is a mixture of small peptides and amino acids extracted from pig brain, given as courses of daily intravenous infusions in many countries, including for vascular dementia. A Cochrane review found six randomized trials with 597 people with vascular dementia. Pooling three of them (420 people), cognition improved by a small standardized amount (0.36), and two trials (379 people) showed better global function; but the trials had high risk of bias, the three that reported funding were all industry-supported, and the reviewers rated the evidence very low quality and warned that any benefit may be too small to be clinically meaningful (Cui 2019). It is not FDA-approved, and no US pharmacy may legally make it.

3 and 4. Semax and Selank: Russian data, not for healthy focus

Semax, a fragment of the hormone ACTH, is registered in Russia for stroke and neurological disease; Selank, built from the immune peptide tuftsin, for anxiety. For cognition specifically, Semax's healthy-volunteer evidence is one brain-scan study: 14 adults given 1% Semax in the nose and 10 given placebo showed a change in resting brain-network activity minutes later, with no test of memory or attention (Lebedeva 2018). Selank's is secondary: Stroop and verbal-fluency tests in a trial where adding it to a benzodiazepine reduced the drug's attention and memory side effects (Medvedev 2015). Neither has been tested for focus or memory in a healthy person in a controlled trial, and neither can be legally prescribed in the US; the hub covers the stroke and anxiety studies, doses and legal status.

5. Dihexa: rat data, and the foundation is cracked

Dihexa is a heavily modified two-amino-acid fragment of angiotensin IV, designed at Washington State University to resist breakdown and cross into the brain when swallowed. In rats it reversed memory deficits caused by the drug scopolamine and by aging and increased the formation of new synapses (McCoy 2013). That paper has carried an expression of concern from its journal since 2021, and the companion paper that tied dihexa's effects to the hepatocyte growth factor system was retracted in 2025 (Benoist 2014). FDA said it found no human exposure data for dihexa by any route of administration (FDA Category 2), and we found no registered human trial. It came off FDA's Category 2 list on April 15, 2026, which did not make it compoundable, and FDA's advisory committee is due to review it by February 2027, as our legal tracker records.

Tested properly, and negative

The two peptides with the best cognition trials are both approved drugs, and both failed.

Intranasal insulin. Insulin is a peptide hormone that also acts in the brain, and nasal devices can deliver it there. In a multisite trial, 289 adults aged 55 to 85 with amnestic mild cognitive impairment or mild Alzheimer's disease took 40 IU or placebo daily for 12 months. In the primary analysis, the difference on the ADAS-Cog-12 cognitive scale was 0.03 points, essentially zero, with no benefit on function or spinal-fluid markers (Craft 2020).

Oral semaglutide. Observational studies had linked GLP-1 drugs to less dementia. In the evoke and evoke+ trials, 3,808 people aged 55 to 85 with amyloid-confirmed early Alzheimer's disease took oral semaglutide up to 14 mg a day or placebo. At 104 weeks, decline on the Clinical Dementia Rating scale was the same in both arms (differences of -0.08 and 0.10 points), and both trials were discontinued (Cummings 2026).

Both results matter for anyone tempted by a research peptide: when brain-active peptides with strong mechanisms were finally tested in large, blinded trials, they did nothing for cognition.

If you are worried about memory, attention or brain fog

Start with a clinician, not a peptide. Memory and concentration complaints often have causes that can be found and treated: poor sleep or sleep apnea, depression and anxiety, thyroid disease, low vitamin B12, medication side effects, alcohol and hearing loss among them. If the concern is dementia, a primary-care clinician or neurologist can test for it and discuss approved treatments. ADHD and anxiety disorders have FDA-approved medicines and therapies with large trials behind them. Do not replace or stop any of those for a research peptide.

Bottom line

The honest ranking is short. Tesamorelin has one positive 20-week trial in older adults and a legal prescription path, used off-label. Cerebrolysin has many small, weak trials and no US approval. Semax and Selank have Russian data in stroke and anxiety, not in healthy focus, and dihexa has rat data whose foundation is under question. The peptides with the strongest trials, intranasal insulin and semaglutide, showed no cognitive benefit. For now, the most effective step for your memory is an evaluation, not a vial.

Frequently asked questions

+−What peptides are good for brain function?

None has been proven to improve thinking in healthy adults. The best evidence for any benefit belongs to tesamorelin, an FDA-approved growth-hormone-releasing peptide that modestly improved executive function in one 20-week trial in 152 older adults, never replicated. The peptides tested most rigorously for memory, intranasal insulin and oral semaglutide, did no better than placebo in large trials. Semax, Selank and dihexa, the peptides most often sold for the brain, have no controlled trial in healthy people.

+−Is there a peptide for memory?

Not one with good evidence. Intranasal insulin, given for a year to 289 people with mild cognitive impairment or early Alzheimer's disease, did not change memory or thinking scores. Oral semaglutide, tested in 3,808 people with early Alzheimer's disease for two years, did not slow decline. Tesamorelin produced a trend toward better verbal memory in one small trial. If your memory is worrying you, see a clinician first: several common causes are treatable.

+−What is the best peptide for brain fog?

There is no peptide with trial evidence for brain fog, which is a description rather than a diagnosis. Common causes include poor or short sleep, sleep apnea, depression, anxiety, thyroid disease, low vitamin B12, iron deficiency, menopause, long COVID and medication side effects, and each has its own test and treatment. A clinician who works through those will do more than any research peptide.

+−What is dihexa?

Dihexa is a synthetic, chemically modified two-amino-acid fragment derived from angiotensin IV, designed at Washington State University to be stable and to cross into the brain when taken by mouth. In rats it reversed drug-induced and age-related memory deficits. It has never been tested in a human trial, FDA found no human exposure data for it by any route, and the two key papers describing it now carry editorial warnings: an expression of concern on the original 2013 study and a 2025 retraction of the 2014 study that described how it works.

+−Is dihexa legal?

It is not FDA-approved, and no US pharmacy may compound it in October 2026. FDA took it off its Category 2 safety-risk list on April 15, 2026 after its nomination was withdrawn, which did not make it compoundable, and its advisory committee is due to review it by February 2027. Pills and powders sold online are unapproved drugs when sold for human use.

+−What is Cerebrolysin peptide?

Cerebrolysin is a mixture of small peptides and amino acids extracted from pig brain, given as a series of daily intravenous infusions in many countries, including for vascular dementia. It is not FDA-approved. A Cochrane review of six trials in 597 people with vascular dementia found small improvements in cognition and global function, but rated the evidence very low quality and said the benefit may be too small to matter clinically.

+−Does semaglutide protect against dementia?

Not in people who already have early Alzheimer's disease. In the evoke and evoke+ trials, 3,808 people aged 55 to 85 took oral semaglutide up to 14 mg a day or placebo, and after two years their decline on the Clinical Dementia Rating scale was the same; both trials were stopped. Earlier observational studies in people with diabetes had suggested less dementia, which is a reason for further research, not for taking semaglutide to protect your memory.

+−Can peptides help ADHD?

We found no ADHD trial of Semax, Selank or any other peptide sold as a nootropic. ADHD has FDA-approved stimulant and non-stimulant medicines and behavioral treatments with decades of trials, and a clinician can confirm the diagnosis and adjust treatment. Do not substitute a research peptide for an ADHD medicine.

Sources

1. StudyBaker 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;69:1420-9. (2012)
2. StudyCraft S et al. Safety, efficacy, and feasibility of intranasal insulin for the treatment of mild cognitive impairment and Alzheimer disease dementia: a randomized clinical trial. JAMA Neurol 2020;77:1099-1109. (2020)
3. StudyCummings JL et al. 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;407:2167-2179. (2026)
4. ReviewCui S et al. Cerebrolysin for vascular dementia. Cochrane Database Syst Rev 2019;(11):CD008900. (2019)
5. StudyLebedeva IS et al. Effects of Semax on the default mode network of the brain. Bull Exp Biol Med 2018;165:653-656. (2018)
6. StudyMedvedev VE et al. Optimization of the treatment of anxiety disorders with Selank. Zh Nevrol Psikhiatr Im S S Korsakova 2015;115:33-40. In Russian. (2015)
7. StudyMcCoy AT et al. Evaluation of metabolically stabilized angiotensin IV analogs as procognitive/antidementia agents. J Pharmacol Exp Ther 2013;344:141-54. Expression of concern, 2021. (2013)
8. StudyBenoist CC et al. 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 2014;351:390-402. Expression of concern, 2021; retracted, 2025. (2014)
9. RegulatoryFDA. Certain bulk drug substances for use in compounding may present significant safety risks: Category 2 list and bulk drug substances nominated but withdrawn (dihexa acetate, Semax, selank acetate). Content current as of April 22, 2026. (2026)