Semax vs Selank — what does the literature actually distinguish between them?

You're roughly right, with the big caveat that almost all of the human data is Russian clinical literature that's hard to fully evaluate from the outside — small samples, methodology that doesn't always translate to Western standards, and limited independent replication.

Semax is an ACTH(4-10) fragment analog and a lot of the interest is around BDNF/neurotrophic signaling and cerebrovascular contexts. Selank is a synthetic analog of the immunopeptide tuftsin and gets studied more for anxiolytic and immunomodulatory effects, often framed around GABA/serotonin systems. So different origins, overlapping "neuro" umbrella. I'd resist treating either as a proven cognitive enhancer in healthy people — that specific claim is where the evidence gets thin fast.

One thing worth adding: they're often discussed as intranasal in the source literature, which matters because it changes what "a study showed X" even means for bioavailability and effect. People sometimes port a finding across routes without noticing.

Not flattening them is the right instinct. They share a country of origin and a research vibe more than a mechanism.

Personal anecdote only, not a recommendation: I found Semax and Selank felt subjectively different to me, which lines up with them being different molecules. But I hold that loosely — expectation effects are enormous in this category and I had no blinding, so I don't put much weight on my own read.