Semax vs Selank: Two Russian Peptides, Two Different Research Paths

What the research says about Semax

Semax has the molecular formula C37H51N9O10S and a molecular weight of 813.93 g/mol (PubChem CID 122178). Rodent studies report it raises expression of brain-derived neurotrophic factor and its TrkB receptor in the hippocampus and basal forebrain after intranasal dosing. Separate rat ischemia studies describe changes across neurotrophin, immune, vascular, and stress-signaling pathways. Other in vitro work shows Semax inhibiting enkephalin-degrading enzymes in human serum.

Human evidence is concentrated in Russian clinical literature. Published studies, most open-label or only partially blinded, describe use in acute ischemic stroke, stroke rehabilitation, cerebrovascular insufficiency, optic nerve disease, glaucoma, and a healthy-volunteer cognition and fMRI study. These studies are not equivalent to the placebo-controlled, blinded trial design that Western regulators expect for drug approval. The Alzheimer's Drug Discovery Foundation's Cognitive Vitality review, one of the more conservative English-language assessments available, concludes that Semax shows mechanistic interest for stroke-adjacent research but that well-conducted published studies remain lacking.

Pharmacokinetic data comes mostly from a rat intranasal study using tritium-labeled Semax, which found that radioactivity reached rat brain tissue within minutes of dosing and that most of the tracked material at the two-minute mark was still intact Semax. A separate literature review reports a rat serum half-life above one hour and notes that oral administration is not effective because peptide bonds break down in the gastrointestinal tract before absorption. No formal human pharmacokinetic dataset (with concentration-time curves, clearance, or absolute bioavailability figures) has been published in the English-language literature reviewed for this article.

What the research says about Selank

Selank, also known as TP-7, has the molecular formula C33H57N11O9 and a molecular weight of 751.89 g/mol (PubChem CID 11765600). It is built on the tuftsin sequence Thr-Lys-Pro-Arg, with a Pro-Gly-Pro tail added for metabolic stability. Researchers describe several candidate mechanisms rather than one confirmed target: GABAergic modulation, enkephalin-degrading enzyme inhibition, monoamine changes, and immune-signaling effects through cytokine gene expression.

Animal literature reports anxiolytic-like findings in mice and rats, an experimental-neurosis model in monkeys, and immune-modulation findings across mouse, rat, and human-cell studies. Human evidence is smaller than Semax's and estimated in the published literature at roughly 250 to 300 patients across five or six studies, none registered on ClinicalTrials.gov. Two of the more cited comparisons: a 62-patient trial comparing Selank with medazepam in patients with generalized anxiety disorder and neurasthenia, and separate work comparing Selank with phenazepam in 60 patients, plus a study of Selank added on top of phenazepam in 70 patients. A resting-state fMRI study in healthy volunteers given a single 0.2 mg dose reported changes in brain connectivity, which is evidence of a central nervous system effect rather than evidence of clinical benefit.

Rat pharmacokinetic data summarized in the published literature show the parent Selank molecule detectable in plasma for only about 7 to 10 minutes after intravenous or intraperitoneal dosing, with an estimated parent half-life of one to three minutes. No dedicated, peer-reviewed human concentration-time pharmacokinetic study has been published. A Russian regulatory dossier reports high intranasal bioavailability, but that figure comes from a drug-registration submission rather than an independently verified, peer-reviewed human study.

Where the two are studied together

The published, peer-reviewed literature reviewed for this article does not contain a placebo-controlled clinical trial studying Semax and Selank in combination. What exists is narrower: both peptides come from the same design lineage and the same Russian pharmaceutical research group, and researchers studying one frequently reference the other in discussing shared mechanisms such as enkephalin-degrading enzyme inhibition. One functional-connectivity fMRI study examined Semax and Selank as separate conditions within the same research program, comparing their individual effects on brain connectivity rather than testing them combined. Outside the formal literature, online research and biohacker communities frequently discuss using the two together, framed informally as a focus-plus-calm pairing, but that is a reported use pattern from online forums, not clinical trial evidence, and this article draws no conclusion from it. If a controlled trial studying the combined use of these two peptides is published, this article will be updated to reflect it.

What a certificate of analysis shows

A certificate of analysis (COA) is a lab document tied to one specific manufacturing batch, or lot, of a research compound. It typically reports the identity of the compound (confirming the material matches its labeled name), its purity as measured by a method such as HPLC or LC-MS, and results from endotoxin testing, which screens for bacterial contamination byproducts that can trigger an immune reaction in cell and animal models. Because a COA is lot-specific, the document for one batch does not describe a different batch, even of the same product. Reading the COA against the batch number on the product label is how a researcher confirms which document applies to the material in hand. Curo publishes lot-specific certificates of analysis for every batch it sells. The testing page explains how Curo tests every lot.

Regulatory status

Neither Semax nor Selank is approved by the FDA for any use in the United States. Both are registered prescription pharmaceuticals in Russia: Semax as a 0.1% and 1% nasal-drop formulation, and Selank as a 0.15% intranasal solution, according to Russian prescribing information cited in the research literature.

In the United States, both peptides were nominated for FDA's 503A Category 2 list, the category the agency uses for bulk drug substances it has flagged as carrying significant safety risk pending further evaluation, largely tied to immunogenicity concerns from aggregation or peptide-related impurities in compounded preparations. FDA's current published list of substances nominated but withdrawn from Category 2 includes both "Semax (heptapeptide)" and "Selank acetate (TP-7)" (FDA, Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks, accessed 2026-09-08). Selank's Category 2 nomination was withdrawn in September 2024; as of mid-2026, it does not sit on FDA's 503A bulks list in any category. Semax followed a more contested path: an FDA Pharmacy Compounding Advisory Committee meeting on July 23 to 24, 2026 produced an 8 to 5 advisory vote favoring inclusion of Semax-related bulk substances on the 503A list, even though FDA's own staff review had recommended against inclusion; that recommendation is nonbinding and FDA has not issued a final rule (Semax FDA Status 2026, published 2026-07-28). Being off Category 2 does not place a substance on the 503A bulks list or mean FDA has approved it; it means the specific safety-risk nomination was withdrawn, leaving the substance without a defined FDA compounding category.

Neither compound appears by name on the World Anti-Doping Agency's 2026 Prohibited List reviewed for this article. WADA's list carries a broad S0 category for non-approved substances, so a compound's absence from an explicit name entry does not by itself establish clearance for athletes; anyone subject to anti-doping rules should check directly with their sport's governing body. All research use of either compound is Research Use Only. Curo's product catalog lists current Semax and Selank research material, sold under Curo's Research Use Only policy.

For background on the research infrastructure both compounds come out of, see Semax: An ACTH Fragment on the FDA's 2026 Review List and Selank: From an Antibody Fragment to Anxiety Research, which cover each compound's individual research record in more depth than the side-by-side format here allows. Curo also maintains related comparisons on other peptide pairs studied together, including BPC-157 vs TB-500, the wolverine stack of BPC-157 and TB-500, and CJC-1295 vs Ipamorelin, plus a broader piece on how Curo verifies its lots against independent records.

For general questions on how documentation and verification work at Curo, see the help center articles on certificate of analysis verification and Curo's quality and testing standard.

FAQ

Are Semax and Selank the same peptide?

No. They are different molecules with different sequences. Semax is built from a fragment of ACTH, a pituitary hormone. Selank is built from tuftsin, an immune-signaling peptide. They share a design approach (both add a Pro-Gly-Pro tail for stability) and come from the same Russian research lineage, but they are structurally distinct compounds studied in different research contexts.

Is either Semax or Selank FDA-approved?

No. Neither is approved by the FDA for any indication in the United States. Both were nominated for FDA's 503A Category 2 compounding-safety list and were later withdrawn from that nomination, which leaves them without a defined FDA compounding category rather than approved or authorized for sale as a drug.

Has anyone studied Semax and Selank together in a clinical trial?

The published literature reviewed for this article does not include a placebo-controlled trial studying the two compounds in combination. Researchers have studied them as separate conditions within the same research program, and online research communities report using them together informally, but that is not clinical trial evidence.