P21 (BDNF-mimetic peptide)
Also known as: Cerebrolysin-derived peptide, PRG, P21 nootropic
P21 (BDNF-mimetic peptide), also called Cerebrolysin-derived peptide or PRG, is a neurotrophic fragment in the BDNF Stimulator class. P21 is sold as a peptide acting on the brain-derived neurotrophic factor pathway, and the research compound it is usually intended to be is P021, a tetrapeptide derivative of the ciliary neurotrophic factor peptide mimetic developed for tauopathy models.
For research use only.
Key Facts
- CAS
- —
- Molecular Weight (MW)
- ≈2292 g/mol
- Half-life
- Unknown (preclinical)
- FDA status
- Not Approved
- Evidence level
- Insufficient Evidence
- Human dose established
- No
- Administration Route
- Not established in humans
- Frequency
- Not established in humans
- Last updated
- Sep 26, 2026
- Reviewed
- Aug 30, 2026
- Targets
- Neurotrophic signaling (claimed)
Vendor price snapshot
Each vendor's price is the median price per mg of its own listings; with fewer than 3 vendors there is no typical range. From public vendor listings collected in Feb 2026, so confirm the live price on the vendor site. Peptide Library does not sell peptides.
- Vendors listing this peptide
- 1
- Listed offers
- 1
- Price per mg
- $11.00/mg
Research summary
Short nootropic peptide associated with Cerebrolysin-derived fragments in research catalogs. Distinct from the p21 CDK inhibitor protein. Not FDA-approved.
Peptide Library's P21 (BDNF-mimetic peptide) profile summarises 4 cited studies listed in the Science section, the compound's regulatory status, and research-protocol parameters reported for it. It is a research reference, not medical advice.
P21 (BDNF-mimetic peptide) dosage: no established human dose
P21 has no established human dosage. No interventional trial is registered and none is indexed. The research compound this is generally intended to be is P021, a neurotrophic peptide mimetic derived from a ciliary neurotrophic factor fragment, and its published dosing is entirely rodent: 500 nmol/kg per day by oral gavage in aged rats, or 60 nmol per gram of feed given continuously to Alzheimer-model mice. Both are oral, both run for months, and neither converts into a subcutaneous microgram dose.
No established human dosage.
Human clinical evidence: None identified.
Preclinical research: The P021 literature is a coherent, long-running rodent programme from a small number of groups, covering cognitive ageing, Alzheimer models and retinal pathology, with treatment periods measured in months. It reports increased BDNF expression downstream, which is where the marketing name comes from. What it does not contain is a human study, a registered trial, a parenteral route, or any pharmacokinetic basis for converting a rodent oral dose in nmol/kg into an injected dose in a person. Animal dosing is not converted into a human equivalent anywhere on this page.
Animal dosing is not converted into a human dose anywhere on this page. Where research figures appear below, they are reported as studied, not recommended.
| Human dosing established | No |
|---|---|
| Route | Not established in humans |
| Evidence level | Insufficient Evidence |
| Last reviewed | 2026-09-05 |
Preclinical and analog research
Not human dosing evidence. Listed for completeness and never extrapolated to a human dose.
| Study / context | Population | Dose | Route | Frequency | Duration | Outcome studied | Source |
|---|---|---|---|---|---|---|---|
| Preclinical — chronic oral P021 in aged rats and Alzheimer-model micePreclinical · Preclinical | Female Fisher rats aged 19-21 months, and 3xTg-AD mice | 500 nmol/kg body weight per day (289.15 mcg/kg) by gavage in the rats; 60 nmol per gram of feed in the mice | Oral | Once daily by gavage, or continuously in feed | 88 days in the rats; from 3 to 21 months of age in the mice | Reduced retinal and macular-degeneration-like pathology | Inhibition of AMD-Like Pathology With a Neurotrophic Compound in Aged Rats and 3xTg-AD Mice. Front Aging Neurosci. 2019. |
| Preclinical — lifelong dietary P021 in an Alzheimer modelPreclinical · Preclinical | 3xTg-AD mice, treated from approximately 3 months of age | 60 nmol of P021 per gram of feed | Oral, in the diet | Continuous | Up to 18 months of treatment | Prevention of dendritic and synaptic deficits and of cognitive impairment | Prevention of dendritic and synaptic deficits and cognitive impairment with a neurotrophic compound. Alzheimers Res Ther. 2017. |
| Preclinical — cognitive ageing in ratsPreclinical · Preclinical | Fisher rats aged 22-24 months | Chronic oral administration of P021; the dose is reported as in the companion studies rather than in this abstract | Oral | — | — | Reduced age-dependent decline in learning and memory, restored neurogenesis, increased BDNF expression, restored cortical and hippocampal synaptic markers | Rescue of cognitive-aging by administration of a neurogenic and/or neurotrophic compound. Neurobiol Aging. 2014. |
Where sources disagree
- This compound is widely sold as BDNF, and vials labelled BDNF are commonly presented as though they contain brain-derived neurotrophic factor. BDNF is a 27 kDa secreted protein, not a short synthetic peptide, and it does not cross the blood-brain barrier in any useful amount when injected. Material sold under this name is a small peptide, and the two should not be conflated.
- Protocols in the range of a few hundred micrograms subcutaneously per day are commonly published for this compound. Every published P021 study dosed by mouth, in nmol/kg or as a concentration in feed, over months. No primary source for a subcutaneous microgram protocol could be identified.
- P021 has not been tested in humans and has no registered trial. The rodent work is chronic and preventive in design, started early and continued for most of the animals' lifespan, which is not a design any short self-directed protocol resembles.
Reconstitution
Common research vial sizes: 5 mg, 10 mg.
| Vial | Bacteriostatic water | Concentration | Per 0.01 mL |
|---|---|---|---|
| 5 mg | 2 mL | 2.5 mg/mL | 25 mcg per 0.01 mL |
| 10 mg | 2 mL | 5 mg/mL | 50 mcg per 0.01 mL |
These figures are arithmetic only — they convert a vial and a volume into a concentration. They are not a recommendation to take any dose.
Calculate reconstitution & dose →Sequence & molecular data
| Molecular formula | C104H157N27O27S |
|---|---|
| Molecular weight | ≈2292 g/mol |
| Half-life | Unknown (preclinical) |
| Appearance | White lyophilized powder |
| Formulation | Lyophilized Powder |
Identifiers link to the public PubChem, FDA Substance Registration (UNII), ChEMBL and DrugBank records for the same entity.
Science
Mechanism of Action
P21 is sold as a peptide acting on the brain-derived neurotrophic factor pathway, and the research compound it is usually intended to be is P021, a tetrapeptide derivative of the ciliary neurotrophic factor peptide mimetic developed for tauopathy models. Preclinical work on P021 describes increased BDNF expression, enhanced neurogenesis in the dentate gyrus, and reduced tau hyperphosphorylation. The important caveat for a reference entry is identity: vendor material sold under the name P21 is not consistently characterised, and the separate and much larger literature on p21 (CDKN1A), a cell-cycle inhibitor protein with no relationship to this peptide, does not apply here. No human trials have been published.
Origin
Synthetic research peptide; catalog identity varies.
Targets
Studies
- Alzheimer's Disease: Challenges and a Therapeutic Opportunity to Treat It with a Neurotrophic Compound
- Diffusion MRI measures detect brain microstructure changes due to early treatment with neurotrophic peptide mimetic P021 in the 3xTg-AD mouse model of Alzheimer's disease
- Effects of a ciliary neurotrophic factor (CNTF) small-molecule peptide mimetic in an in vitro and in vivo model of CDKL5 deficiency disorder (class-level evidence)
- Prevention of dendritic and synaptic deficits and cognitive impairment with a neurotrophic compound (class-level evidence)
Regulatory & research status
P21 (BDNF-mimetic peptide) is not an FDA-approved product. It is sold for laboratory research and has no approved medical use.
| FDA status | Not Approved |
|---|---|
| Availability | Research-Only |
| WADA (sport) | Unknown / Not Listed |
| Library classification | Research-Only |
Benefits
P21 (BDNF-mimetic peptide) side effects
P21 (BDNF-mimetic peptide) has no controlled human safety data. The effects below are reported, not established, and absence from the list is not evidence of safety.
Side Effects
- Unknown
- Product confusion risk
Storage & stability
Lyophilized (freeze-dried) peptide powder is far more stable than the reconstituted solution. Keep sealed vials cold, dry and away from light; long-term storage is typically frozen, with short-term refrigeration for vials in use.
Once reconstituted in bacteriostatic water, keep the solution refrigerated, avoid repeated freeze–thaw cycles and agitation, and label the vial with the reconstitution date and concentration. Discard any solution that turns cloudy or shows particulates.
Degradation rates differ by sequence: peptides containing methionine, cysteine, asparagine or glutamine are more prone to oxidation and deamidation, so shelf life after reconstitution is compound-specific rather than universal.
Read the full guide: how to store peptides before and after reconstitution →
Source: Manning MC, Chou DK, Murphy BM, Payne RW, Katayama DS. Stability of protein pharmaceuticals: an update. Pharm Res. 2010;27(4):544–575. (PMID 20143256). General guidance for research handling; not product-specific instructions.
P21 (BDNF-mimetic peptide): frequently asked questions
What is P21 (BDNF-mimetic peptide)?
Short nootropic peptide associated with Cerebrolysin-derived fragments in research catalogs. Distinct from the p21 CDK inhibitor protein. Not FDA-approved.
How does P21 (BDNF-mimetic peptide) work?
P21 is sold as a peptide acting on the brain-derived neurotrophic factor pathway, and the research compound it is usually intended to be is P021, a tetrapeptide derivative of the ciliary neurotrophic factor peptide mimetic developed for tauopathy models. Preclinical work on P021 describes increased BDNF expression, enhanced neurogenesis in the dentate gyrus, and reduced tau hyperphosphorylation.
Is P21 (BDNF-mimetic peptide) FDA approved?
No. P21 (BDNF-mimetic peptide) is not approved by the FDA for any indication and is categorised as research-only. It has not been reviewed for safety or efficacy as a medicine, and published research should be read as investigation rather than established use.
What is the half-life of P21 (BDNF-mimetic peptide)?
Reported half-life for P21 (BDNF-mimetic peptide) is Unknown (preclinical). Half-life describes how long the compound persists in circulation, not how long any effect lasts, and published figures vary with route of administration, formulation and the population studied.
What peptides are similar to P21 (BDNF-mimetic peptide)?
Compounds most often compared with P21 (BDNF-mimetic peptide) include Cerebrolysin, Cortexin, Dihexa and Noopept. They are grouped by shared mechanism or research area rather than by equivalence, and their regulatory status and evidence base differ.
References
- Alzheimer's Disease: Challenges and a Therapeutic Opportunity to Treat It with a Neurotrophic Compound — Biomolecules, 2022External reference
- Diffusion MRI measures detect brain microstructure changes due to early treatment with neurotrophic peptide mimetic P021 in the 3xTg-AD mouse model of Alzheimer's disease — Magn Reson Imaging, 2026External reference
- Class-level evidence — Effects of a ciliary neurotrophic factor (CNTF) small-molecule peptide mimetic in an in vitro and in vivo model of CDKL5 deficiency disorder — J Neurodev Disord, 2024External reference
- Class-level evidence — Prevention of dendritic and synaptic deficits and cognitive impairment with a neurotrophic compound — Alzheimers Res Ther, 2017External reference
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Compiled by Peptide Library Editorial · Reviewed Aug 30, 2026 · Updated Sep 26, 2026 · Version 3
This P21 (BDNF-mimetic peptide) profile is compiled from published literature (4 cited studies linked above), public regulatory records and chemical registries. It describes what research reports; it is not medical advice, and nothing here is a dosing recommendation for humans. Peptide Library does not sell peptides. Editorial policy · How profiles are compiled · Report an error
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