Head to head
P21 vs Selank
A comparison decided mostly by evidence: Selank has been studied in people to a degree the other has not.
Verdict
One has been tested in people; the other has not
What you are actually choosing between
Both are classed here as nootropics, so this is a within-class choice: the mechanism is broadly shared and what separates them is kinetics, route, and how much has actually been tested.
The overlap is focus and cognition. On this site's goal weighting — an editorial priority score, not a measure of effect size — P21 rates 5/5 for focus and cognition and Selank rates 3/5. Outside that overlap only Selank goes further, carrying weight for recovery and sleep; P21's declared goals stop at the overlap.
The evidence
This is the part that decides most of it. Selank has approval from a regulator somewhere, though not a current FDA or EMA label — a registered Russian medicine; the trials are small and Russian-language. P21 has animal and cell data only, and no controlled human dosing trials — there is essentially no human data at all. That gap is the headline, and it is a statement about the literature rather than a promise about you: a compound with trial data can still do nothing for your case, and one without it is unproven rather than disproven.
How they differ in practice
P21 is a subcutaneous injection and a nasal spray; Selank is a nasal spray and a subcutaneous injection. Neither one forces you onto a needle.
No half-life is published for either compound in this dataset. That absence is itself information: it means the pharmacokinetics have not been characterized well enough to quote, so both dosing schedules — once daily for P21, twice daily for Selank — are convention.
Committed time differs: P21 runs 4 weeks, Selank runs 2 weeks.
Risk and difficulty
Selank is rated intermediate here and P21 advanced. That rating is about how much can go wrong in handling, dosing and monitoring, not about how well either works.
Source notes
What the evidence actually says
Verbatim, so you can check the verdict above against what it was built from.
P21
THERE IS ESSENTIALLY NO HUMAN DATA ON P21. It is a small adamantylated tetrapeptide derivative (Ac-DGGL-amide) of an 11-residue active region of ciliary neurotrophic factor, designed to be orally available and blood-brain-barrier permeable. The entire evidence base is preclinical: transgenic and aged rodent models of Alzheimer disease and Down syndrome, reporting increased neurogenesis and BDNF signaling and reduced tau hyperphosphorylation, from the group that developed it at the New York State Institute for Basic Research. No human trial has been published, no human pharmacokinetic or toxicology data exists, and no approved product exists anywhere. Rodent work dosed it orally or subcutaneously; the subcutaneous and intranasal routes listed here reflect how unregulated users actually take it. The range given is deliberately narrow and conservative and is extrapolated from that practice, NOT from any dose-finding study - treat it as a description, not a recommendation. It is frequently confused with the unrelated cell-cycle protein p21 (CDKN1A); they are not the same thing.
Selank
A synthetic heptapeptide analogue of the immune peptide tuftsin, again with a Pro-Gly-Pro tail added for stability. Its character is anxiolytic rather than stimulant, which is why it is usually paired with, not substituted for, Semax. Like Semax it is a Russian-registered intranasal medicine (commonly a 0.15% solution) and is NOT approved in the US or EU; the human evidence is small Russian trials in generalised anxiety disorder and adjustment disorder, some comparing it against benzodiazepines such as phenazepam, and it has not been independently replicated in Western trials. Route matters: it is an intranasal drug, not an injectable. Russian clinical dosing runs to roughly 1800-2700 mcg per day divided across two or three administrations; the per-dose range here reflects the more conservative doses typical of non-clinical use rather than the full trial daily total. Plasma half-life is minutes, so no hourly figure is listed. Courses are conventionally short (10-14 days) rather than continuous.
Side by side
The numbers
| Attribute | P21 | Selank |
|---|---|---|
| Class | Nootropic | Nootropic |
| Routes | Subcutaneous, Intranasal | Intranasal, Subcutaneous |
| Dose range | 250 mcg–1 mg (typical 500 mcg) | 150 mcg–900 mcg (typical 300 mcg) |
| Frequency | Once daily | Twice daily |
| Half-life | Not characterized | Not characterized |
| Cycle length | 4 weeks | 2 weeks |
| Experience | Advanced | Intermediate |
| Evidence | Animal / cell data only | Approved elsewhere |
| Contraindications |
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| Side effects |
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Goals
Where they overlap, and where they do not
| Goal | P21 | Selank |
|---|---|---|
| focus and cognition | P21: 5/5 | Selank: 3/5 |
| neuroprotection | P21: 5/5 | Selank: 2/5 |
| recovery and sleepone only | P21: — | Selank: 4/5 |
| immune supportone only | P21: — | Selank: 2/5 |
| longevityone only | P21: 2/5 | Selank: — |
They overlap on 2 goals and diverge on 3. Weights are this site’s editorial priority score out of 5 — how central a goal is to why people use a compound. They are not effect sizes and two 5s do not mean two equal results.
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Educational information only, not medical advice. Talk to a licensed clinician before starting, changing, or stopping anything.