Semax and Cerebrolysin occupy the same corner of research, compounds studied for cognitive and neuroprotective effects with their deepest roots in Russian and Eastern European practice, and they are searched together constantly. Chemically and evidentially they could hardly be more different. One is a seven-residue synthetic peptide with a defined sequence. The other is an enzymatic digest of pig brain containing thousands of molecular species. The comparison is really a choice between two philosophies of what a neuro research compound should be.
Semax: a defined fragment with a designed tail
Semax is a heptapeptide built from a fragment of adrenocorticotropic hormone: the ACTH(4-7) sequence Met-Glu-His-Phe, extended with the tripeptide Pro-Gly-Pro. The ACTH fragment carries the neurotropic activity that had been observed for melanocortin-related sequences since the 1970s, activity separate from any hormonal effect on the adrenal gland, and the Pro-Gly-Pro tail was added to resist enzymatic degradation and extend the peptide's action.
Developed at Moscow institutions in the 1980s and 90s, Semax has a defined mechanism literature: work by Dolotov and colleagues showed it increases expression of brain-derived neurotrophic factor and its receptor TrkB in the hippocampus, and the compound is studied in models of ischaemia, cognitive load and attention. It is registered as a drug in Russia, usually administered intranasally, with clinical use in stroke and cognitive indications there; it holds no approval in Western regulatory systems, and its controlled-trial base is largely Russian-language.
For a researcher the important properties are its definedness: one sequence, synthesisable to verifiable purity, one certificate of analysis per batch, as supplied in the Semax vial and the Semax nasal spray, the intranasal format mirroring how the compound has historically been administered.
Cerebrolysin: a hydrolysate, not a molecule
Cerebrolysin is a different kind of object. It is produced by enzymatic breakdown of purified porcine brain proteins, yielding a solution of low-molecular-weight peptides and free amino acids. It has no single active ingredient; the preparation is the ingredient, standardised by process rather than by structure. It has been manufactured in Austria for decades and is registered in dozens of countries, mostly across Europe, Asia and the Middle East, for dementia and stroke indications; like Semax it has no FDA approval.
The claimed rationale is that the peptide fraction mimics the action of endogenous neurotrophic factors. Because the material can be given in controlled trials like any drug product, it has accumulated a substantial trial literature, and that literature has been evaluated at the highest evidentiary level: a Cochrane review of Cerebrolysin for acute ischaemic stroke, most recently updated by Ziganshina and colleagues, found no benefit on survival or dependency and noted an excess of non-serious adverse events. The dementia literature, reviewed by Plosker and Gauthier, is more mixed, with reported short-term cognitive effects and persistent questions about heterogeneity and trial quality.
What the comparison actually turns on
Definition first. Semax is one molecule; Cerebrolysin is thousands. A mechanism claimed for Semax can in principle be tested molecule-to-target; a mechanism claimed for Cerebrolysin is a claim about a mixture, and batch-to-batch equivalence rests on process control rather than on sequence verification. For laboratory research this difference is close to decisive, and it is the same extract-versus-molecule divide we drew for Thymalin vs Thymosin Alpha-1.
Evidence second, and the shape is unusual: the mixture has the larger controlled-trial base, including the negative Cochrane result, while the defined peptide's trials are smaller and largely inaccessible to non-Russian readers. Neither compound's cognitive claims survive to approval-grade evidence in Western systems.
Practicality third. A porcine brain derivative raises sourcing and biological-material questions a synthetic peptide simply does not have.
The takeaway
Semax is a defined, synthetic ACTH-fragment heptapeptide with a mechanism literature centred on BDNF and a Russian clinical tradition, particularly intranasal. Cerebrolysin is a standardised brain hydrolysate with a large but discouraging top-tier trial record. They share a research territory and almost nothing else. For work that needs a verifiable single compound, the choice makes itself; for reading the literature, keep the two evidence bases separate, because they are not measuring the same kind of thing. Semax's nearest defined-peptide neighbour, and the more informative comparison for nootropic-peptide research, is covered in Semax vs Selank.
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References
1. Dolotov, O. V., Karpenko, E. A., Inozemtseva, L. S., et al. (2006). Semax, an analog of ACTH(4-10) with cognitive effects, regulates BDNF and trkB expression in the rat hippocampus. Brain Research, 1117(1), 54-60.
2. Ziganshina, L. E., Abakumova, T., & Hoyle, C. H. (2020). Cerebrolysin for acute ischaemic stroke. Cochrane Database of Systematic Reviews, 7, CD007026.
3. Plosker, G. L., & Gauthier, S. (2009). Cerebrolysin: a review of its use in dementia. Drugs and Aging, 26(11), 893-915.
