P21 (P021) Reconstitution Calculator

This page is about the research peptide P21 (also written P021 or Peptide 21), a synthetic tetrapeptide — Ac-DGGL(A)G-NH₂ — engineered as a mimetic of ciliary neurotrophic factor (CNTF). It's easy to confuse with the unrelated p21 protein (also called p21^CIP1/WAF1 or CDKN1A), the cell-cycle inhibitor that p53 switches on to halt cell division — that's a natural tumor-suppressor protein, not something sold as a research compound. If your interest is p53 signaling, CDK inhibition, or tumor biology, you want the protein; this calculator is for the neurogenic peptide.

P021 was developed in Khalid Iqbal's lab by paring the neurotrophic activity of Cerebrolysin down to a single small molecule, with an adamantane group and a C-terminal amide added so it survives in the body and reaches the brain. In rodent studies it stimulates new neuron growth in the hippocampus and raises BDNF, apparently by blocking LIF signaling, which in turn dampens GSK-3β and reduces the abnormal tau phosphorylation tied to Alzheimer-type pathology. Importantly, all of this evidence is preclinical — the picture comes from animal models, with no human trials.

It's sold as a lyophilized powder, so add bacteriostatic water down the vial wall, swirl gently, and don't shake. As an illustrative example, a 5 mg vial with 3 mL of bacteriostatic water gives 1.67 mg/mL, so a 500 mcg dose would be 0.3 mL — 30 units on a U-100 insulin syringe. Treat any dose figure as extrapolated from animal work rather than an established human amount, since there's no validated clinical dosing.

Unusually for a peptide, P021 was deliberately engineered to be orally bioavailable and to cross the blood-brain barrier — that's the whole point of the adamantane modification, and the rodent studies mostly gave it by mouth. Because of that, it shows up not only as a reconstituted injectable-style solution but also as capsules and nasal sprays, and the pre-made sprays aren't something you reconstitute. This calculator covers the lyophilized powder; which route you'd use is a separate research decision from how you mix it.

In the Iqbal-lab literature P021 was tested in models of Alzheimer's disease, Down syndrome, traumatic brain injury, and neurodevelopmental disorders such as CDKL5 deficiency — which is where the "autism" interest comes from — all in rodents, none in people. Because its core action is driving cell proliferation and neurogenesis, the main theoretical safety concern is anyone with active or prior cancer, and caution is also raised for seizure disorders, autoimmune conditions, pregnancy, and still-developing brains. It isn't FDA-approved and has no human safety data, so it should be treated as an early-stage research compound.