Semax and Selank are searched as rivals because they arrive together: two short Russian peptides, both nasal drops, both from the same Moscow manufacturer, both sold as research vials in the West. Read from their sequences and labels, they are cousins rather than twins. They share a three-residue tail and a manufacturer, and differ in what they are built from, what they are registered for, how much each drop holds and how much evidence stands behind them. This page sets the two side by side and reports what each source states. It compares compounds; it recommends neither.
Taking them together is covered on the Selank and Semax stack page. Each compound's full record is on its own dosage page: Semax and Selank. Medibact's guides cover the compounds themselves: Semax and Selank.
Side by side
| Semax | Selank | |
|---|---|---|
| Sequence | Met-Glu-His-Phe-Pro-Gly-Pro | Thr-Lys-Pro-Arg-Pro-Gly-Pro |
| Built from | ACTH(4-7) + Pro-Gly-Pro | Tuftsin (Thr-Lys-Pro-Arg) + Pro-Gly-Pro |
| Molecular weight | 813.9 | 751.9 |
| Russian registration | 0.1% nasal drops (nootropic); 1% (ischaemic stroke) | 0.15% nasal drops (anxiety states, neurasthenia, adaptation disorders) |
| Micrograms per drop | 50 (0.1%), 500 (1%), stated on the label | 75 at a 0.05 mL drop, arithmetic; not stated on the label |
| Labelled daily range | 500–5,000 mcg (0.1%), 3–5 days, to 14 | ~900 mcg, 14 days, repeatable |
| PubMed title/abstract records | 208 | 68 |
| Trial-tagged papers | 4 (stroke ×2, motor neuron disease, optic nerve) | 3 (anxiety, against or with benzodiazepines) |
| ClinicalTrials.gov | 0 | 2, both false matches |
| FDA 503A (Sept 2023 interim list) | Category 2 | Category 2 |
| FDA compounding committee, July 2026 | Voted in favour of adding to the 503A list (non-binding) | Not on the agenda |
Sources: PubChem CIDs 9811102 and 11765600; the Russian drug-register entries for both products, the trial papers and the Category 2 listing as recorded, with their sources, on this site's Semax and Selank pages (read 2026-09-18 and 2026-09-20); PubMed and registry counts read 2026-09-24; the committee vote as reported by the National Community Pharmacists Association on 2026-07-31.
The shared tail
The one structural thing the two have in common is their last three residues. Semax is Met-Glu-His-Phe, residues 4 to 7 of ACTH, followed by Pro-Gly-Pro; papers of 2024 and 2025 describe it as a "non-hormonal" or "noncorticotropic" ACTH analogue (PMIDs 40650034 and 39442746), meaning it keeps none of ACTH's action on cortisol. Selank is Thr-Lys-Pro-Arg, the peptide tuftsin, followed by the same Pro-Gly-Pro, and rat studies of it call it "a peptide analogue of tuftsin" (PMIDs 36322304 and 31625062). So the tail is shared and the fronts are unrelated: one from a pituitary hormone, one from an immune peptide. The registrations follow the fronts, not the tail: one is registered for cognition and stroke, the other for anxiety.
Drops, strengths and the microgram gap
Both products are measured in drops of a stated percentage, and the percentage is the concentration: 0.1% is 1 mg/mL, 0.15% is 1.5 mg/mL, 1% is 10 mg/mL. The Semax instruction does the conversion itself, 50 mcg per drop at 0.1%, which fixes its drop at 0.05 mL. The Selank label states drops and no micrograms; at the same 0.05 mL drop, one drop of 0.15% is 75 mcg, and its regimen of two drops per nostril three times a day is twelve drops, about 900 mcg a day. That figure rests on the drop size, not on the Selank label, and the Selank page shows the assumption.
The resulting ranges are not alike. Semax 0.1% runs from 500 to 5,000 mcg a day, a tenfold range set by indication; its stroke studies used the 1% strength at 12 and 18 mg a day, more than any Selank figure by a factor of thirteen or more. Selank's labelled regimen is one figure for one course. The vendor pages that sell both as research vials state them in a single band, 250 to 600 mcg, often for injection under the skin, a route neither registration uses.
What the evidence holds for each
Semax has the larger literature: 208 PubMed records on 2026-09-24, four carrying the clinical-trial tag, in acute stroke (1997, 30 patients, 12 and 18 mg a day), motor neuron disease (2007, 27 patients, no effect on the disease measures), optic-nerve disease (2000) and stroke rehabilitation (2018, 110 patients, 6,000 mcg a day). Selank has 68 records and three trial-tagged papers, all in anxiety: against medazepam in 62 patients (2008), against phenazepam in 60 (2014) and alongside phenazepam in 70 (2015); none of the three abstracts states the dose. Neither compound has a registration on ClinicalTrials.gov, and every trial for either found for this page is published in a Russian journal.
The one study that gave both is not a comparison of treatments. In 2020, 52 healthy volunteers received Semax, Selank or placebo and had resting-state brain scans before and 5 and 20 minutes after. The authors report "general and specific effects" of each on connectivity between the right amygdala and the right temporal cortex. It measured scans over twenty minutes, not anxiety, memory or any outcome a person would notice, and it is the whole of the head-to-head record found for this page.
Regulatory status, and where it diverged in 2026
Neither compound is approved in the US or the EU. Both were placed in Category 2 of FDA's interim 503A bulks list in September 2023. Their paths separated in July 2026: FDA's Pharmacy Compounding Advisory Committee, meeting on 23 and 24 July, voted in favour of adding Semax to the 503A bulks list, together with BPC-157, KPV, TB-500, MOTS-c and Epitalon, according to the National Community Pharmacists Association's report of 31 July. The same report states that the committee's votes are recommendations, not binding on FDA, and that the addition needs formal approval. Selank was not among the substances considered.
The arithmetic per vial
Research vials are commonly labelled 5 mg and 10 mg for Semax and 5 mg for Selank. Units on a U-100 syringe = mcg ÷ (mcg per mL) × 100.
| Amount | 5 mg + 2 mL (2.5 mg/mL) | 10 mg + 2 mL (5 mg/mL) | 30 mg + 3 mL (10 mg/mL) |
|---|---|---|---|
| 250 mcg | 10 units | 5 units | 2.5 units |
| 300 mcg | 12 units | 6 units | 3 units |
| 600 mcg | 24 units | 12 units | 6 units |
| 900 mcg | 36 units | 18 units | 9 units |
The table applies to either compound at a given concentration; what differs in practice is the vial each is sold in. The calculator presets for Semax and Selank work other vial sizes, and the reconstitution pages for Semax and Selank set out each vial.
What is not established
No clinical trial has compared Semax with Selank on any outcome. Neither has a trial by injection under the skin, the route vendor figures often describe. Neither has a registration outside Russia's register and literature, and the July 2026 committee vote is not an approval. Which compound, if either, suits anyone is a decision for a prescriber; this page reports sources, not a choice.
Sources and dates
Opened 2026-09-24: the PubMed abstracts of Panikratova YR et al., Dokl Biol Sci 2020;490:9-11 (PMID 32342318), and PMIDs 40650034, 39442746, 36322304 and 31625062 for the structural descriptions; PubMed counts for semax[tiab], selank[tiab] and both together, with a metformin control; ClinicalTrials.gov v2 intervention counts; the National Community Pharmacists Association report of 2026-07-31 on the July 2026 committee vote. Carried from this site's Semax, Selank and Selank-Semax pages (sources opened 2026-09-18 and 2026-09-20 and listed there): the Russian register entries, the trial abstracts, PubChem records and the Category 2 listing. Drop and unit arithmetic by this site. Corrections go to the contact page.