Peptides Studied for Cognitive Function

PT-141 (bremelanotide) is a synthetic cyclic heptapeptide and non-selective melanocortin receptor agonist (MC3R/MC4R) derived as an active metabolite of Melanotan II. It is FDA-approved (2019) for hypoactive sexual desire disorder (HSDD) in premenopausal women, marketed as Vyleesi. Unlike PDE5 inhibitors that target vascular blood flow, PT-141 acts on the brain's melanocortin system to increase libido and arousal, effective in both men and women through central nervous system pathways.

Exenatide is a 39-amino-acid GLP-1 receptor agonist (MW ~4186.6 g/mol) originally derived from exendin-4, a peptide found in the saliva of the Gila monster (Heloderma suspectum). It was the first GLP-1 receptor agonist approved by the FDA, with Byetta (twice-daily injection) approved in April 2005 and Bydureon (once-weekly extended-release) approved in January 2012, both for type 2 diabetes. Exenatide shares approximately 53% sequence homology with human GLP-1 and is resistant to DPP-4 degradation.

Difelikefalin is a synthetic D-amino acid tetrapeptide (MW ~714.9 g/mol) that acts as a selective peripheral kappa-opioid receptor (KOR) agonist. It was FDA-approved in August 2021 (Korsuva) for the treatment of moderate-to-severe pruritus associated with chronic kidney disease (CKD-aP) in adults undergoing hemodialysis. Difelikefalin was specifically designed to not cross the blood-brain barrier, thereby providing peripheral kappa-opioid agonism without the central dysphoric and psychotomimetic effects associated with centrally acting kappa agonists.

Cagrilintide is a long-acting synthetic analog of human amylin, a peptide hormone co-secreted with insulin by pancreatic beta cells. It is being developed by Novo Nordisk both as a standalone agent and in fixed-dose combination with semaglutide (CagriSema). The CagriSema combination targets complementary appetite pathways — amylin acts on hindbrain satiety circuits while GLP-1 acts on hypothalamic and gut pathways. In the REDEFINE Phase 3 program, CagriSema achieved 20.4% weight loss at 68 weeks. Novo Nordisk filed for FDA approval in 2026.

Danuglipron (PF-06882961) is a small-molecule, non-peptide oral GLP-1 receptor agonist developed by Pfizer. NOTE: Danuglipron is NOT a peptide — it is a synthetic small molecule included here for comparison with peptide-based GLP-1 agonists. It is in Phase III development for type 2 diabetes and obesity. Danuglipron was initially studied as a twice-daily formulation, but Pfizer shifted focus to a once-daily modified-release formulation after the twice-daily version showed high discontinuation rates due to GI side effects.

Thymosin beta-4 (Tβ4) is a naturally occurring 43-amino acid protein found in virtually all human and animal cells. It is the most abundant member of the beta-thymosin family and plays fundamental roles in cell migration, wound healing, and tissue repair. Tβ4 is distinct from TB-500, which is a synthetic peptide containing only the active heptapeptide region (Ac-LKKTETQ) of Tβ4. The full-length protein is being developed as RGN-259 (RegeneRx Biopharmaceuticals) eye drops for dry eye, neurotrophic keratopathy, and other ophthalmic conditions, with multiple Phase II/III clinical trials completed or ongoing.

Neuropeptide Y (NPY) is a 36-amino-acid peptide (MW ~4271.7 g/mol) that is one of the most abundant and widely distributed neuropeptides in the mammalian brain. It is a potent orexigenic (appetite-stimulating) peptide and plays critical roles in energy homeostasis, stress response, anxiety regulation, circadian rhythms, and cardiovascular function. NPY acts through a family of G-protein-coupled receptors (Y1, Y2, Y4, Y5). It is an endogenous reference molecule and a major drug target, not a therapeutic agent itself.

Vasoactive Intestinal Peptide (VIP) is a 28-amino-acid neuropeptide (MW ~3326.8 g/mol) widely distributed in the central and peripheral nervous systems, lungs, and gastrointestinal tract. It is a potent vasodilator, bronchodilator, and immunomodulator. The synthetic form aviptadil (RLF-100) was investigated for COVID-19-associated acute respiratory distress syndrome (ARDS) and has been studied in pulmonary arterial hypertension. VIP is also used diagnostically in VIPoma identification.

B-type natriuretic peptide (BNP) is a 32-amino-acid cardiac hormone (MW ~3464 g/mol) secreted primarily by ventricular cardiomyocytes in response to myocardial wall stress from volume overload or pressure overload. It is both a critical diagnostic biomarker for heart failure (BNP/NT-proBNP assays) and the basis for the therapeutic agent nesiritide (recombinant BNP). Originally identified in porcine brain tissue, hence the historical name "brain natriuretic peptide."

Cholecystokinin (CCK) is a well-characterized endogenous gut-brain peptide hormone released by I-cells in the duodenum and jejunum in response to dietary fat and protein. It is one of the most extensively studied satiety hormones, with decades of research confirming its role in meal termination, gallbladder contraction, and pancreatic enzyme secretion. CCK acts via CCK-A (peripheral) and CCK-B (central) receptors. While its physiology is firmly established, therapeutic use for weight loss is limited by rapid tachyphylaxis (tolerance).

Ghrelin is a 28-amino acid peptide hormone produced primarily by the stomach that serves as the endogenous ligand for the growth hormone secretagogue receptor (GHS-R1a). It is the only known circulating orexigenic (appetite-stimulating) hormone. Ghrelin stimulates growth hormone release, increases appetite, promotes fat storage, and coordinates energy metabolism between the gut and brain. It requires a unique post-translational modification (n-octanoylation at Ser3) for biological activity. Pharmaceutical analogs like anamorelin have been developed for cancer-related cachexia.

Cerebrolysin is a brain-derived peptide complex consisting of low-molecular-weight neuropeptides (25%) and free amino acids (75%), produced by enzymatic hydrolysis of purified porcine brain proteins. All peptide fragments are below 10 kDa, allowing them to cross the blood-brain barrier. It is approved in over 40 countries (Europe, Asia, Russia) for stroke, traumatic brain injury, and dementia, but is NOT FDA-approved in the United States. Clinical evidence is mixed — some trials show benefit in stroke recovery while a 2023 Cochrane review found no clear mortality benefit.

NAD+ is a fundamental coenzyme present in all living cells that serves as a critical electron carrier in metabolic reactions and a substrate for enzymes including sirtuins, PARPs, and CD38. NAD+ levels decline approximately 50% between ages 40 and 60. While not a peptide, NAD+ and its precursors (NMN, NR) are frequently discussed in peptide communities. IV NAD+ infusions are popular at anti-aging clinics, though large-scale human efficacy trials are limited.

Epidermal Growth Factor (EGF) is a 53-amino acid protein discovered by Stanley Cohen, who shared the 1986 Nobel Prize in Physiology or Medicine for this work. EGF plays a fundamental role in cell growth, proliferation, and differentiation. In medicine, recombinant human EGF (rh-EGF) is used in wound healing products and is approved in several countries (South Korea, Cuba, China) for diabetic foot ulcers and other wound indications. In cosmetics, it is marketed as oligopeptide-1 or sh-oligopeptide-1 for anti-aging. The wound healing evidence is strong; cosmetic anti-aging evidence is more limited.

Noopept (GVS-111, omberacetam) is a synthetic dipeptide derivative (N-phenylacetyl-L-prolylglycine ethyl ester, MW ~318.4 g/mol) developed at the Russian Academy of Sciences. It is not a true peptide but a peptidomimetic prodrug of the endogenous neuropeptide cycloprolylglycine. Noopept is approved in Russia for treatment of cognitive disorders of vascular and traumatic origin, but has not undergone rigorous clinical evaluation by Western regulatory standards.

N-Acetyl Selank Amidate is a modified version of Selank with N-acetylation and C-amidation for increased metabolic stability. Base Selank is approved in Russia for anxiety and cognitive disorders. This modified form is popular for intranasal use in the research peptide community.

Demoxytocin is a synthetic analog of oxytocin with a deaminated N-terminal amino group that provides improved resistance to enzymatic degradation (aminopeptidases). It was developed as a more stable alternative to oxytocin for clinical use, particularly for lactation support and labor induction. It can be administered intranasally or buccally, offering convenience over IV oxytocin. Demoxytocin has also attracted interest for its anxiolytic and pro-social effects, similar to oxytocin but with a longer duration of action.

Retinalamin is a polypeptide bioregulator derived from bovine retinal tissue, developed by Geropharm (Russia) as a neuroprotective and retinoprotective agent. It stimulates tissue-specific proliferation of retinal and pigmented epithelial cells, modulates neurotrophic factors including BDNF, and protects against retinal cell apoptosis. Clinical studies report 82% improvement in visual acuity in pediatric abiotrophy cases and significant retinal sensitivity increases in glaucoma patients. It is a registered pharmaceutical in Russia used for glaucoma, diabetic retinopathy, and retinal degenerative conditions.

Selank is a synthetic heptapeptide (Thr-Lys-Pro-Arg-Pro-Gly-Pro, MW ~751.89 g/mol) developed at the Institute of Molecular Genetics of the Russian Academy of Sciences. It is a structural analogue of the immunomodulatory peptide tuftsin with an added Pro-Gly-Pro sequence for stability. Approved in Russia as an anxiolytic and nootropic nasal spray, it crosses the blood-brain barrier to enhance GABAergic neurotransmission, modulate monoamine systems, and regulate neuropeptide Y signaling. A 2008 study of 62 patients with GAD showed Selank comparable to medazepam for anxiety reduction but with no sedation, cognitive impairment, or dependence risk. Half-life is approximately 2-10 minutes.

Semax is a synthetic heptapeptide (Met-Glu-His-Phe-Pro-Gly-Pro) derived from adrenocorticotropic hormone (ACTH) fragment 4-10, with an added Pro-Gly-Pro sequence for metabolic stability. Molecular weight is approximately 813.88 g/mol (formula C37H51N9O10S). Discovered in Russia during the 1980s as part of government-funded neuropeptide research, it is approved in Russia and Ukraine for the treatment of ischemic stroke, cognitive disorders, encephalopathy, and optic nerve atrophy. Despite its ACTH origin, Semax does not activate adrenal corticosteroid production, acting selectively on brain-specific pathways.