Nootropic peptides are short amino-acid chains promoted to sharpen memory, focus or mood. The best-known are Semax and Selank, nasal drops approved only in Russia, and Dihexa, a lab compound tested only in animals.[1][2][7] NAD+ is often sold alongside them. None is FDA-approved, and most of the human evidence comes from small Russian studies.[10][11]

What are nootropic peptides?

“Nootropic” describes anything claimed to improve thinking. Nootropic peptides differ from prescription drugs for ADHD or dementia in one key way: none has passed the large, placebo-controlled trials that regulators in the US or Europe require.

Three of the four compounds in this category are true peptides. Semax and Selank each contain seven amino acids, and Dihexa is a modified two-amino-acid fragment of angiotensin IV.[1][2][7] NAD+ is different: it is a coenzyme made from vitamin B3, not a peptide, and it is grouped here because the same clinics and sellers offer it for “brain energy”.[15]

For calming and sleep-related uses, see our sleep peptides page. For brain aging, see longevity peptides.

Browse all cognitive peptides

See all 13 cognitive peptides ↓

How nootropic peptides work

Almost everything known about how these compounds act on the brain comes from rats and cell cultures:

  • Semax: a single nasal dose raised the growth factor BDNF and activated its receptor in the rat hippocampus, a brain area involved in memory.[3]
  • Selank: it slows the breakdown of enkephalins, the body’s own calming peptides, which may explain its anti-anxiety effect.[4]
  • Dihexa: its developers proposed that it boosts the HGF/c-Met growth pathway to build new connections between nerve cells. The main paper showing this was retracted in 2025.[8]
  • NAD+: it powers energy reactions in every cell and feeds enzymes involved in DNA repair, which is why it is marketed for mental energy.[15]

In a Russian brain-imaging study of 52 healthy volunteers, both Semax and Selank changed activity in brain networks compared with placebo.[18] Changes on a scan are not the same as better memory or focus, and that study did not test either.

Semax vs Selank

Semax and Selank come from the same Moscow institute and share the same stabilizing Pro-Gly-Pro tail, but they are used for opposite purposes.

SemaxSelank
Based onACTH fragment[1]Tuftsin, an immune peptide[2]
Russian useStroke and cognitive problems (prescription)[1]Anxiety (over the counter)[2]
Typical effect describedStimulating, focusCalming
Best human study110 stroke patients, open-label[6]62 anxiety patients vs a benzodiazepine[5]

The Semax label lists disorders accompanied by anxiety as a contraindication, which matters because the two are often combined online.[1] No trial has tested them together. Each profile covers the full research and dosing.

Nasal drops, injections and pills

How a nootropic peptide is taken matters, because almost all of the human research used one route and much of what is sold online uses another.

  • Semax was studied as nasal drops. Injectable versions are sold online, but FDA found no safety data for injected Semax and no human pharmacokinetic studies.[10]
  • Selank is also a nasal drop. Its Russian maker reports that it is well absorbed through the nose and clears from the blood within about 5 minutes.[2]
  • Dihexa worked when swallowed in rats, where its half-life was about 12.7 days after an intravenous dose. No human data exist, so how long it would stay in a person’s body is unknown.[7]
  • NAD+ is sold as IV drips and injections. In a small pilot, a slow 6-hour infusion raised blood NAD+, with no change for the first 2 hours.[21] Oral precursors such as nicotinamide riboside have far more human data.[16]

Dosing for each compound, where any has been studied, is on its profile. Category pages do not give protocols.

What the human evidence actually shows

Semax and Selank: small Russian studies

Every human study of Semax and Selank was run in Russia, and most were small. In 110 people recovering from stroke, those given Semax had higher blood BDNF and better daily-living scores than those not given it, but patients were not randomized to placebo.[6] Selank relieved anxiety about as well as the benzodiazepine medazepam in 62 patients, again with no placebo group.[5] FDA reviewers found no human pharmacokinetic studies of Semax,[10] and a 2021 US pharmacology review called Selank poorly studied.[17]

Dihexa: rats, a retraction and a failed relative

Dihexa improved water-maze learning in rats with drug-induced amnesia and in old rats.[7] It has never been tested in a published human trial. In 2021 the journal flagged several papers from the developers’ lab over possible image manipulation,[20] and in 2025 the key paper on its mechanism was retracted after a university investigation found falsified or fabricated data.[8] Fosgonimeton, an injected drug its maker said converts to Dihexa in the blood,[20] did not beat placebo on memory or daily function in a phase 2/3 Alzheimer’s trial.[9]

NAD+: more data, but not for thinking

NAD+ precursors such as nicotinamide riboside have been tested in far larger trials. In NOPARK, 410 people with early Parkinson’s disease took nicotinamide riboside or placebo for a year; symptoms progressed slightly more on the supplement, and the authors concluded it was not disease-modifying.[16] No trial has shown that NAD+ injections or drips improve memory or focus.

Safety, legality and sports rules

  • FDA approval: none of these compounds is FDA-approved for any use.[11] Semax and Selank are approved medicines in Russia only.[1][2]
  • Compounding: FDA staff recommended against allowing Semax in compounding, but its advisory committee reportedly voted 8 to 5 in favor in July 2026; FDA has not issued a final decision.[10][12] Selank’s nomination was withdrawn, and FDA says important human safety information is lacking.[11] Dihexa left FDA’s safety-risk category in April 2026 only because its nomination was withdrawn, not because it was cleared.[11] NAD is still under FDA evaluation.[19]
  • Product quality: Belgian authorities found Semax and Selank in seized products of unknown origin, and found these and other “cognitive-enhancing” research peptides freely sold online.[13] “Research use only” vials are not tested for identity, purity or dose.
  • Sports: Semax, Selank and Dihexa are not named on WADA’s 2026 Prohibited List. Dihexa has no approval anywhere, so in our reading it falls under category S0 (non-approved substances), banned at all times; because Semax and Selank are approved in Russia, their status is unclear. WADA also limits IV infusions to 100 mL per 12 hours outside hospital care, which would apply to NAD+ drips larger than 100 mL.[14]
  • Who should be cautious: the Russian labels exclude pregnancy, breastfeeding, and (for Semax) people with seizures or acute psychiatric conditions.[1][2]

This is general information, not medical or legal advice. Speak with a doctor about memory or focus problems, which can have treatable causes.