Compounds in this category
Semax and Selank are the two most documented compounds here. Both came out of the Russian Academy of Sciences in the 1980s and 1990s. Semax is registered in Russia for ischemic stroke and cognitive dysfunction. Selank is registered for generalized anxiety. The published trial base is largely Russian-language and clinically smaller than Western Phase 3 standards. Independent replication outside Russia is thin. That is the honest evidence picture, not a marketing failure.
Cerebrolysin is a different case. It is a porcine-brain-derived peptide mixture sold in more than 50 countries for Alzheimer's disease and post-stroke recovery. Multiple Phase 3 trials and Cochrane reviews exist. Effect sizes are modest. The compound is not FDA-approved in the United States and is regulated as a drug, not a supplement, in the markets that allow it.
Dihexa sits in a different evidence tier. It is an angiotensin IV analog developed by Joseph Harding's lab at Washington State University. Preclinical work suggests strong hepatocyte growth factor activity in rat hippocampal cultures. Zero human trials have been published. Anything written about Dihexa in human cognition is extrapolation from rodents.
Methylene blue belongs in its own awkward subcategory. It is an FDA-approved drug for methemoglobinemia, used clinically since the 1890s. The cognitive use case is off-label, built on mitochondrial electron transport effects observed in rodent studies and a few small human imaging studies. Pharmacy-grade methylene blue differs sharply from industrial methylene blue, which carries heavy-metal contamination.
Khavinson bioregulators like Cortexin, Cerluten, and Pinealon are short peptides developed by Vladimir Khavinson's group in St. Petersburg starting in the 1970s. Animal data is published in volume. Western peer-reviewed clinical replication is sparse. The compounds are sold as supplements in Russia and as research chemicals elsewhere. Research Use Only (RUO) labeling applies in the United States and the European Union.
Mechanism overlap
Most cognitive peptides in this category act on one of four systems. Some target BDNF and neurotrophic signaling (Cerebrolysin, Semax, Dihexa indirectly via HGF). Some modulate serotonergic and GABAergic tone (Selank). Methylene blue affects mitochondrial electron transport. The Khavinson family is proposed to act through short-peptide regulation of gene expression. Different mechanism, different tier of evidence, different regulatory status. They are not interchangeable, and stacking them does not multiply effect sizes in any controlled human trial.
Cognitive screening: what the evidence does not cover
No peptide in this category currently has Phase 3 efficacy data for cognitive enhancement in healthy adults. The clinical literature that does exist tests these compounds in stroke recovery, age-related cognitive decline, post-concussion syndrome, or specific anxiety disorders. Extrapolating efficacy to a healthy 30-year-old executive is not supported by the trial design or patient populations enrolled.
What this category is not. It is not a curated list of compounds that reliably make people smarter. Published effect sizes range from "statistically detectable in a Russian Phase 2" to "rat-only and unconfirmed." Where dosing appears in each compound page, it is reported as it appears in the cited literature. PeptScope does not frame dosing as personal advice.
What is missing from cognitive enhancement research is also worth flagging. Long-term safety data beyond 12 months is rare for the off-label members of this category. Mechanism is often plausible. Translation to humans remains the open question for the preclinical-only compounds. Readers screening this category for usable evidence should start with the trial-stage compounds and treat the rest as unverified.