Cerebrolysin

Cerebrolysin is unlike everything else in this catalogue in one fundamental respect: it is not a single compound. It is a preparation made by breaking down purified pig brain protein with enzymes, producing a mixture of low-molecular-weight peptides and free amino acids. There is no sequence to state and no molecular weight to quote, because it is not one substance.

That has consequences worth understanding. A defined peptide can be synthesised identically anywhere; a biological extract is defined by its process, and different batches are matched by specification rather than by being chemically identical. It is closer in kind to a vaccine or a blood product than to the other items on this site.

The rationale is that the brain maintains itself with a range of neurotrophic and neuroprotective peptides, and that a preparation derived from brain tissue may contain fragments resembling several of them at once. Instead of isolating one active molecule, the approach keeps the mixture and studies it as a whole — an older strategy in pharmacology, and one that makes mechanism unusually hard to pin down.

• A multi-component preparation: Whether a mixture can achieve what single molecules have not is a genuine question in neurology, where isolated neurotrophic factors have repeatedly failed on delivery and stability.

• Clinical use in several countries: It is licensed and used in parts of Europe and Asia in stroke and dementia settings, which means human data exists — a rarity for anything in this category.

• Contested trial evidence: Systematic reviews of that human data have reached conflicting conclusions. The disagreement is itself informative about how difficult outcomes in this field are to measure.

• Size and the barrier problem: The peptides in the preparation are small by design, because size is the main obstacle to reaching the brain. This is the practical argument for a digest rather than an intact protein.

Neurotrophic factors are the proteins that keep neurons alive and support their connections, and they are the obvious thing to reach for after brain injury or in degeneration. The difficulty is delivery: they are large, they break down quickly, and the blood–brain barrier excludes them. Decades of work on supplying them directly has produced more lessons about the obstacles than about the biology.

The approach here is to start from brain tissue and break its proteins into fragments small enough to be practical. The resulting mixture contains many short peptides, some of which are proposed to retain activity resembling that of the factors they came from. The claim is not that any single component does the work, but that the combination is active.

This makes mechanism genuinely difficult to establish. With one molecule and one receptor, an effect can be traced. With a mixture of many peptides acting at unknown targets, the most that can usually be shown is that the preparation as a whole produces a measurable change. Studies have reported effects on neuronal survival and connection formation in laboratory models, but attributing them to anything specific in the mixture remains an open problem.

Cerebrolysin has been examined in people at a scale few compounds in this field reach. It has been used clinically for decades in several countries, and randomised trials exist in acute stroke and in dementia. Some report benefit; systematic reviews, including Cochrane assessments, have concluded that the evidence does not establish it.

Being derived from animal tissue also raises manufacturing and consistency questions that synthetic peptides do not, and it is not approved in the UK or the US. What sets it apart from almost everything else in this category is the scale on which it has been examined in people, and that the question of how a mixture achieves its effects is still genuinely open.

Semax and Selank come from the same broader tradition of neuropeptide research and share the pattern of substantial regional clinical use with limited independent replication. All three are defined more by their research histories than by their mechanisms.

Pinealon is a short bioregulator peptide studied in the nervous system through a different proposed mechanism again, and is frequently encountered alongside these compounds.