Quick Answer
Semax is an ACTH(4-10) analog targeting BDNF upregulation, dopaminergic and serotonergic modulation, and neuroprotection, while Selank is a tuftsin analog targeting GABA-A receptor modulation, enkephalinase inhibition, and anxiolysis – they were developed in the same Moscow laboratory using the same Pro-Gly-Pro stabilisation strategy but address fundamentally different neurological targets. Both are approved in Russia (Semax for cerebral ischaemia, Selank for generalised anxiety disorder) and both face PCAC review in the United States, with Semax scheduled for July 24, 2026 and Selank referred but with no date set.
Comparison Summary
| Dimension | Semax | Selank |
|---|---|---|
| Sequence | Met-Glu-His-Phe-Pro-Gly-Pro (MEHFPGP) | Thr-Lys-Pro-Arg-Pro-Gly-Pro (TKPRPGP) |
| Parent fragment | ACTH(4-10) – adrenocorticotropic hormone | Tuftsin (Thr-Lys-Pro-Arg) – IgG heavy chain Fc region |
| Stabilisation | Pro-Gly-Pro C-terminal tail | Pro-Gly-Pro C-terminal tail |
| Primary mechanism | BDNF/trkB upregulation, dopaminergic modulation | GABA-A allosteric modulation, enkephalinase inhibition |
| Primary effect profile | Nootropic, neuroprotective, neurotrophic | Anxiolytic, immunomodulatory, neuroprotective |
| Russian approval | Yes (VED list, Dec 7 2011). Cerebral ischaemia, migraine, trigeminal neuralgia | Yes (LRS-003338/09, 2009). GAD, neurasthenia, adjustment disorders |
| FDA status | Category 2 removed April 15, 2026. PCAC July 24, 2026 (Day 2) | Category 2 removed September 20, 2024 (nominator withdrawal). Referred to PCAC, no date set |
| Strongest human evidence | 110-patient stroke rehabilitation (non-randomised) | 60-patient placebo-controlled GAD trial (statistically significant) |
| Delivery | Intranasal (0.1% and 1% solutions) | Intranasal (0.15% solution) |
| Developer | Ashmarin and Myasoedov, Institute of Molecular Genetics, Moscow (1982) | Myasoedov, Institute of Molecular Genetics, Moscow |
| BDNF involvement | Primary mechanism (1.4x protein, 3x mRNA) | Secondary mechanism (2.7x in hippocampal cultures) |
| Modified variants | N-Acetyl Semax Amidate (enhanced stability) | N-Acetyl Selank (acetylated N-terminus) |
How They Differ
Structural origins
Semax and Selank share identical length (seven amino acids) and an identical C-terminal stabilisation tail (Pro-Gly-Pro), but their N-terminal parent fragments come from entirely different biological sources. Semax derives from ACTH(4-10), the neurotrophic fragment of adrenocorticotropic hormone that retains the parent molecule’s cognitive effects without its hormonal activity. Selank derives from tuftsin (Thr-Lys-Pro-Arg), a naturally occurring tetrapeptide cleaved from the Fc region of immunoglobulin G that functions as an immunostimulatory signal.
Both were developed at the same institution – the Institute of Molecular Genetics of the Russian Academy of Sciences in Moscow, under the direction of N.F. Myasoedov – and both use the same design strategy of appending the Pro-Gly-Pro tripeptide to protect the parent fragment from enzymatic degradation. This shared design principle with different parent sequences is what makes them a natural comparison pair: same stabilisation engineering, deliberately different targets. For the full context of this design programme, see the nootropic and neuropeptide compounds hub.
Mechanism comparison
Semax’s primary mechanism involves upregulation of brain-derived neurotrophic factor (BDNF) and its trkB receptor in the hippocampus, alongside dopaminergic modulation (D1 receptor density increase, tyrosine hydroxylase upregulation) and serotonergic effects. Preclinical transcriptome studies have identified thousands of genes affected by Semax in rat brain tissue. For the full mechanism with specific study data, see the Semax guide.
Selank’s primary mechanism operates through allosteric modulation of GABA-A receptors at a non-benzodiazepine site, with a preclinical transcriptomic study identifying 45 GABAergic genes altered within one hour of administration. Selank also inhibits enkephalinase, extending endogenous enkephalin signalling, and modulates serotonin transporter expression. For the full mechanism with specific study data, see the Selank guide.
Both compounds upregulate BDNF, but through different pathways and to different degrees. Semax’s BDNF upregulation is its central mechanism; Selank’s BDNF effect is secondary to its primary GABAergic activity. This distinction matters because it implies different downstream effects despite a shared molecular outcome.
The bottom line: Semax is primarily a neurotrophic and nootropic compound (BDNF/dopamine), while Selank is primarily an anxiolytic and immunomodulatory compound (GABA-A/enkephalin) – their mechanisms are complementary rather than overlapping.
Evidence Comparison
Both compounds have clinical evidence exclusively from Russian institutions, and both face the same evidence-concentration critique: all published human data comes from groups with programme ties to the Institute of Molecular Genetics. No independent Western replication of either compound’s clinical outcomes has been published.
| Evidence dimension | Semax | Selank |
|---|---|---|
| Largest clinical study | 110 patients (stroke rehabilitation, non-randomised) | 70 patients (adjunctive trial, open-label add-on to phenazepam) |
| Best-controlled trial | Non-randomised, unblinded | 60-patient placebo-controlled (47% vs 34% HAM-A reduction, p<0.05) |
| Active-comparator trials | None published | Two (vs medazepam, vs phenazepam): comparable anxiolysis |
| Preclinical transcriptomics | Three major studies (2,000+ genes, 1,400+ genes, time-course) | One major study (45 GABAergic genes in 1 hour) |
| Primary clinical indication | Stroke rehabilitation, cognitive decline | Generalised anxiety disorder |
| Independent verifiability | Transcriptome data yes; clinical outcomes no | Gene expression data yes; clinical outcomes no |
| Placebo-controlled evidence | None | One trial (statistically significant but modest effect size) |
Selank has the stronger evidence by conventional clinical trial standards: it has a placebo-controlled trial with a statistically significant result (p<0.05), whereas Semax’s largest clinical study is non-randomised. However, Semax has a deeper preclinical transcriptomics base, with three major studies versus one for Selank. Semax also has additional clinical evidence in optic nerve disease that Selank lacks. For full details of each compound’s clinical and preclinical data, see the individual guides linked above.
The bottom line: Selank has modestly stronger controlled human evidence (one placebo-controlled trial), while Semax has deeper preclinical molecular characterisation and broader clinical indication coverage.
Regulatory Status Comparison
Both compounds are approved in Russia but face different regulatory timelines in the United States. Semax has a concrete PCAC review date: July 24, 2026, Day 2 of the scheduled meeting (Docket FDA-2025-N-6895), where it will be evaluated for three indications (cerebral ischaemia, migraine, trigeminal neuralgia). Selank was referred to PCAC after its nomination was withdrawn from Category 2 in September 2024, but no review date has been scheduled.
Neither compound is licensed by the MHRA or approved by the TGA. In Russia, Semax was added to the vital and essential drugs list (VED) on December 7, 2011; Selank was registered under LRS-003338/09 in 2009. Both are manufactured by Peptogen JSC (Semax) or through approved Russian pharmaceutical channels (Selank).
| Jurisdiction | Semax | Selank |
|---|---|---|
| Russia | Approved (VED list 2011) | Approved (2009) |
| FDA (USA) | PCAC review July 24, 2026 | Referred to PCAC, no date |
| MHRA (UK) | Not licensed | Not licensed |
| TGA (Australia) | Not approved | Not approved |
The bottom line: Semax is further along the US regulatory timeline with a scheduled PCAC date, while Selank’s US pathway remains undefined after its nomination withdrawal.
Safety Profile Comparison
Both compounds have favourable safety profiles based on Russian post-marketing data, though neither has long-term safety data from controlled Western-standard trials.
Semax’s reported side effects are mild: headache, dizziness, and nasal irritation. It does not produce hormonal suppression (despite its ACTH origin) and no dependence has been documented. Selank’s profile is notable for what it lacks: unlike benzodiazepines (its clinical comparators), Selank has shown no sedation, no cognitive impairment, no dependence, and no withdrawal symptoms across its clinical trial data and 15+ years of Russian post-marketing observation.
The safety comparison favours neither compound over the other – both appear well-tolerated within the constraints of the available data. The critical caveat for both is that all safety data originates from Russian institutions and post-marketing surveillance systems, with no independent Western replication. The individual compound guides cover each safety profile in full detail.
The bottom line: Both compounds show mild, well-tolerated side effect profiles in available data, with Selank’s absence of sedation and dependence being its distinguishing safety advantage relative to the benzodiazepine drug class it was designed to improve upon.
Which Compound for Which Purpose?
The Semax-Selank comparison is not a question of which is “better” but rather which addresses the relevant research question:
- Semax’s evidence base centres on neuroprotection after ischaemic injury, cognitive enhancement in healthy and impaired populations, and broad neurotrophic gene expression – it is, at its core, a neurotrophic compound.
- Selank’s evidence base centres on anxiolysis without the drawbacks of benzodiazepines and on immunomodulatory activity inherited from its tuftsin parent – it is, at its core, an anxiolytic compound.
In standard Russian clinical practice, the two compounds are frequently used in combination, based on the rationale that their mechanisms are complementary rather than overlapping. No controlled combination study has been published, and this combined use is based on clinical experience rather than randomised evidence. The combination use question is covered in more depth in the cluster hub page.
Semax and Selank represent a deliberate split in design: the same laboratory used the same stabilisation strategy on two different biological fragments to create one compound for cognition and one for anxiety, making them perhaps the clearest example of rational peptide engineering in the nootropic space.
Neither Semax nor Selank is approved by the FDA, MHRA, or TGA for any therapeutic indication. Both are approved only in Russia. The information on this page is for educational purposes only and does not constitute medical advice. No content on PeptideGuider.com should be interpreted as a recommendation to use any compound. Always consult a qualified healthcare professional before making any decisions about your health.