Dihexa vs Semax vs Selank: of the three, only Semax and Selank have been tested in people, in small Russian studies of 110 people or fewer, and both are approved medicines in Russia.[11][13][7][12] Dihexa has only rat, mouse and cell data, and its main mechanism paper was retracted in 2025.[1][2] None of the three is FDA-approved, and no trial has ever compared them.
They are grouped together online as “nootropic peptides,” but they work on different systems and were developed for different problems. For the full research on each, see our Dihexa profile, Semax profile and Selank profile, or browse the nootropic peptides hub.
At a glance
| Dihexa | Semax | Selank | |
|---|---|---|---|
| Origin | Angiotensin IV fragment, Washington State University[1] | ACTH fragment, Moscow[7] | Tuftsin (immune peptide), Moscow[12] |
| Proposed target | HGF/c-Met growth signaling[2] | BDNF; dopamine and serotonin (animal data)[10] | Enkephalins and GABA (lab data)[16] |
| Main use studied | Memory in rats[1] | Stroke and cognitive problems[7] | Anxiety[12] |
| Human trials | None published | Small, mostly open-label[8] | Small, no placebo arm[13] |
| Approved anywhere? | No[5] | Prescription drug in Russia[7] | Over the counter in Russia[12] |
| US status | Not approved[5] | Not approved; advisers voted 8 to 5 for compounding[9] | Not approved; nomination withdrawn[5] |
How each one is thought to work
- Dihexa is a modified two-amino-acid fragment of angiotensin IV, built to resist breakdown and reach the brain when swallowed.[1] Its developers said it boosts hepatocyte growth factor (HGF) signaling through the c-Met receptor to grow new synapses. The 2014 paper that made that case was retracted in 2025 after a university investigation found falsified or fabricated data.[2]
- Semax is a 7-amino-acid peptide based on a piece of the hormone ACTH, given as nasal drops. In rats a single nasal dose raised the brain growth factor BDNF in the hippocampus about 1.4-fold.[10] FDA reviewers called its mechanism poorly understood.[8]
- Selank is a 7-amino-acid analog of tuftsin, a natural immune peptide, with the same stabilizing tail as Semax. Lab studies suggest it slows the breakdown of the body’s calming enkephalins and affects the GABA system that benzodiazepines act on.[16]
In simple terms: Dihexa is pitched as a “brain growth” compound, Semax as a stimulating focus and recovery drug, and Selank as a calming one.
Evidence quality: animals vs people
Dihexa: animal studies only
- Rats: oral Dihexa improved maze learning in rats given an amnesia-causing drug and in old rats.[1] That 2013 paper has carried an expression of concern since 2021.[20]
- Mice: a Chinese study in Alzheimer’s model mice reported better memory and less brain inflammation.[19]
- People: none. Athira Pharma, which licensed Dihexa, told investors in 2021 that its injectable drug fosgonimeton is rapidly converted to Dihexa in the blood.[3] Fosgonimeton then failed to beat placebo on memory and daily function in the LIFT-AD Alzheimer’s trial.[4]
Semax: small Russian human studies
- Stroke recovery: in an open study of 110 patients, those given Semax had higher blood BDNF and better daily-living scores than those not given it.[11]
- Healthy volunteers: brain-imaging studies found changes in resting brain networks after nasal Semax or Selank versus placebo.[15]
- FDA’s 2026 review found the evidence for stroke, migraine and nerve pain insufficient and found no human pharmacokinetic studies.[8]
Selank: small Russian anxiety trials
- Versus medazepam: in 62 people with generalized anxiety or neurasthenia, Selank relieved anxiety about as well as this benzodiazepine.[13]
- Added to phenazepam: in 70 patients, adding Selank led to faster improvement and fewer benzodiazepine side effects such as sedation.[14]
- A US pharmacology review called Selank poorly studied.[16]
Results people are looking for
| Goal | Dihexa | Semax | Selank |
|---|---|---|---|
| Memory and focus | Rat maze learning only[1] | Label use for cognitive problems from vascular disease; no rigorous trials in healthy people[7] | Mild cognitive effects reported alongside anxiety relief[13] |
| Anxiety | No data | Label lists anxiety disorders as a contraindication[7] | Main studied use[13] |
| Stroke or brain injury | Rat injury models only | Russian stroke studies[11] | No data |
For Selank vs Semax specifically, read our Selank vs Semax comparison. If sleep is your main concern, see DSIP vs melatonin.
Side effects and safety
- Dihexa: FDA says it found no human exposure data by any route.[5] It is designed to boost the HGF/c-Met pathway, which drives growth and spread in many cancers,[17] so long-term cancer risk is an open question that no study has tested. In rats its half-life was about 12.7 days after an IV dose.[1]
- Semax: the Russian label lists only mild nasal irritation with long use, and lists seizures, acute psychiatric conditions and anxiety disorders among contraindications.[7] FDA raised concerns about immune reactions to injected products, impurities and possible abuse potential.[8]
- Selank: the label lists allergic reactions and an unpleasant taste; it is not for pregnancy, breastfeeding or anyone under 18.[12]
Legal and FDA status in 2026
- Dihexa: not approved. FDA had placed dihexa acetate in its compounding safety-risk category. It was removed from that category in April 2026 only because the nomination was withdrawn, and FDA said it plans to consult its advisory committee by the end of February 2027.[5][6]
- Semax: not approved. FDA staff recommended against allowing it in compounding, but the advisory committee voted 8 to 5 in favor on July 24, 2026. FDA has not issued a final decision.[8][9]
- Selank: not approved; its compounding nomination was withdrawn.[5]
- Sport: none is named on WADA’s 2026 list. Dihexa, unapproved everywhere, likely falls under the non-approved substances category; Semax and Selank, approved in Russia, are less clear.[18]
For the bigger regulatory picture, see what changed with the FDA peptide ban in 2026.
Cost and access
None of the three is sold through US pharmacies as an approved drug, so there are no official US prices. Semax and Selank are sold as nasal drops in Russia.[7][12] We don’t list sellers, and products marketed online are unregulated.
Who each might suit: questions for your clinician
- “I want help with focus or memory.” Ask whether a proven cause, such as sleep problems, depression, thyroid disease or medication side effects, has been ruled out first.
- “I have anxiety.” Ask about approved treatments with large trials. Selank’s data are small and unblinded.[13]
- “I’m recovering from a stroke.” Semax’s stroke studies are Russian and mostly open-label; ask what rehabilitation and approved options are available.[11]
- “I’ve read Dihexa is more potent than BDNF.” That claim came from lab dishes, not people, and the follow-up mechanism paper was retracted.[2]
The verdict
On evidence, Selank and Semax are ahead of Dihexa, but only because something beats nothing: they have small human studies and decades of Russian use, while Dihexa has none in people. What isn’t known is just as important. No trial has compared the three, none has proven cognitive benefits in healthy people, and long-term safety is unknown for all of them, most of all for Dihexa.
