Selank vs semax

The difference is the front half of the molecule. Selank's first four residues are tuftsin, a fragment of the immunoglobulin G heavy chain. ^[1] Semax's first four are ACTH(4-7), a fragment of adrenocorticotropic hormone. ^[2] The shared Pro-Gly-Pro tail was added to each for stability. That origin split shapes everything else: selank's literature centres on anxiety models and immune genes, and semax's on stroke models and brain-derived neurotrophic factor (BDNF).

Both came out of the same Moscow circle. Selank was designed at the Institute of Molecular Genetics of the Russian Academy of Sciences with the V.V. Zakusov Research Institute of Pharmacology. ^[1] Semax's developers published a 1997 review of 15 years of its design and study. ^[10]

The two peptides match on length and tail and differ on charge, mass, targets and the kind of research behind them. We built this table from PubChem, PubMed, the June 2026 Poisons Standard, the WADA 2026 List and our own catalogue, all checked on 29 September 2026.

The identifiers come from PubChem. ^[4][5] The enzyme target is from the 2001 comparison, ^[6] the GABA work from a 2018 binding study ^[11] and the semax binding sites from a 2006 rat study. ^[12] The first-record years come from our PubMed search. ^[8][13] The selank programme is three small Russian anxiety studies with 60 to 70 patients each, compared against benzodiazepines. ^[14][15][16] The semax programme includes a 1997 study of 30 stroke patients against 80 controls and a 2018 study of 110 patients after ischaemic stroke. ^[17][18] The FDA rows come from its compounding lists and meeting page. ^[19][20]

Two rows matter at the bench. Selank carries a positive charge and is strongly water-loving; semax is closer to neutral and less polar. And semax contains methionine, one of the residues Sigma-Aldrich lists as prone to air oxidation, while selank contains no cysteine, methionine or tryptophan. ^[21] The fuller selank picture is in our selank research overview.

Selank's proposed mechanisms come from Russian laboratory work, and there are two. It inhibits enzymes that break down enkephalins, and it modulates GABA receptor binding.

The enzyme work came first. In human serum, selank inhibited enkephalin-degrading enzymes with an IC50 of 20 µM. ^[6] The GABA work came later: a 2018 radioligand study reported that selank acted on [3H]GABA binding as a positive allosteric modulator, and that it blocked the modulating effect of diazepam and olanzapine. ^[11] In the frontal cortex of 30 rats, 45 of 84 neurotransmission genes changed expression 1 hour after selank or GABA. ^[1]

The immune thread comes from tuftsin. Selank's designers kept tuftsin's sequence intact and added Pro-Gly-Pro to improve metabolic stability and lengthen its action. ^[1] These are rodent, cell and serum results. They describe what researchers measured, and a 2021 US review still calls selank a poorly studied Russian drug. ^[22]

Semax's proposed mechanism centres on BDNF, a growth factor that supports nerve cells, plus specific binding sites whose receptor has not been named. The work is in rats and cells.

In rat basal forebrain membranes, tritium-labelled semax bound in a time-dependent, specific and reversible way that needed calcium, with a dissociation constant of 2.4 nM. The same 2006 study reported a rise in BDNF in the basal forebrain 3 hours after semax, and none in the cerebellum. ^[12] A second 2006 rat study reported a 1.4-fold rise in hippocampal BDNF protein and a 1.6-fold rise in trkB receptor phosphorylation. ^[23]

Two more lines of work are chemical. Semax inhibits enkephalin-degrading enzymes too, at an IC50 of 10 µM in human serum, ^[6] and a later study traced that effect in plasma to aminopeptidases. ^[24] Semax also has a high affinity for copper(II) ions, which is why chemists study it in metal-binding assays. ^[25] Papers call semax an ACTH(4-10) analogue and also ACTH(4-7)PGP; both names describe the same seven residues. ^[23][2]

Five published studies tested selank and semax in the same experiment. All are laboratory or imaging work from Russian groups, and none is a clinical comparison in patients.

Read the breakdown row with care. The 2006 study measured selank in blood plasma and semax in the presence of nerve cells, so the two results come from different media. ^[24] The fMRI study is the closest thing to a human comparison. It reported brain connectivity after a single exposure and made no claim about anxiety, memory or any clinical outcome. ^[7]

A Belgian medicines laboratory that found both peptides in seized preparations wrote in 2020 that, to its knowledge, neither had completed any clinical trials. ^[28] That statement sits alongside the small Russian clinical reports covered below, which used no placebo in patients.

No study we found tested selank and semax given together. PubMed holds 14 records that name both peptides. ^[8] Their abstracts describe each peptide tested in its own group, and two records have no abstract to check.

Peptides Collective sells no vial that combines them. Our three stacks hold other compounds, so each peptide comes in its own vial. Both sit in our cognitive and sleep research peptides range.

Neither peptide has a published adverse-event rate from a controlled trial. The record for both is thin, and it comes from small Russian reports, animal work and one US regulator.

Selank

• 70 patients with anxiety disorders (2015). Adding selank to phenazepam was reported to reduce phenazepam's undesirable effects, rated on the UKU scale. No separate rate is given for selank. ^[16]
• Anaesthetised cats (2005). Selank given into a vein lowered arterial pressure by 32% for the first 1 to 3 minutes and raised cerebral blood flow by 24%. ^[29]
• Mouse embryonic stem cells (2017). Selank reduced the share of cells becoming GABA-positive neurons by 61%. The authors concluded the peptides tested showed no toxic effect. ^[27]

Semax

• 187 patients with cerebrovascular insufficiency (2005). The authors described side effects in a "minor percent" of patients without naming them or giving a rate. ^[30]
• 73 patients with posthypoxic encephalopathy (1999). EEG showed episodes of paroxysmal activity after semax in some cases, and the authors called for EEG monitoring at first exposure. ^[31]

Both, from the US FDA. The FDA lists selank acetate and semax on its compounding list of withdrawn nominations. For each it states a possible risk of immunogenicity from aggregation and peptide-related impurities, and for each it says it lacks the safety information needed. ^[19] These observations give no basis for a tolerability conclusion about either peptide.

Neither selank nor semax is named in the Poisons Standard. We searched the full text of the June 2026 instrument (F2026L00633), which commenced on 1 June 2026, and found no entry for either. The instrument does list corticotrophin, the full ACTH hormone, in Schedule 4, and it has no entry for ACTH fragments by name. ^[3] "Not named" means neither has a schedule of its own. Our guide to peptide scheduling under the Poisons Standard explains how state law and the schedules fit together.

For sport, neither is named on the WADA 2026 Prohibited List, effective 1 January 2026. Class S0 prohibits at all times any pharmacological substance with no current approval by a governmental health authority for human therapeutic use. Class S2.2.2 covers corticotrophins and their releasing factors, naming corticorelin and tetracosactide. ^[9] We have not verified how WADA classifies either peptide. Sport Integrity Australia states that possession or use of prohibited peptide products can lead to an anti-doping rule violation, and points athletes to Global DRO to check a substance. ^[32]

In the United States, both appear on the FDA's list of withdrawn compounding nominations. ^[19] Semax was on the agenda of the FDA's compounding advisory committee on 24 July 2026, for uses including cerebral ischaemia; selank was not. ^[20]

Peptides Collective sells both for laboratory research use only, each as a 10mg vial of lyophilised powder at A$58. Stock ships from Western Australia with tracking.

The Selank 10mg product page and the Semax 10mg product page each link the certificate of analysis for the batch currently on sale. Every batch is tested by an independent lab before sale, for purity by HPLC and identity by mass spectrometry. You can also search the certificate library by the batch number printed on the vial.

Because the two peptides differ by 62 g/mol, a mass spectrum tells them apart. Calculated from PubChem's exact masses, the protonated ion should sit near m/z 752.44 for selank and m/z 814.36 for semax, with doubly charged semax near m/z 407.68. ^[4][5] Our guide on how to read a peptide certificate of analysis explains the HPLC trace, the mass spectrum and net peptide content.

Selank and semax share a length, a tail and a Moscow origin, and they differ in the fragment each is built on. The only direct comparisons are five laboratory and imaging studies, led by a 2001 enzyme assay and a 2020 fMRI study in 52 healthy adults. Neither is named in the June 2026 Poisons Standard or on WADA's 2026 List. For a research vial, the batch certificate is what confirms which peptide is inside.