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Research chemical Published: animal data only Emerging use

P21: dosing, reconstitution and evidence

A ciliary neurotrophic factor peptide analog studied for neurogenesis and for reducing tau pathology in animal models of Alzheimer's.

Also known as P021, Cntf peptide analog

Educational research reference Cognitive & Sleep
Quick reference. Everything you need to run P21 — dosing, frequency, reconstitution math for the vial sizes people actually buy, and what it stacks with. For anything specific to your situation, ask the Guru.

P21 quick start

Route
SubQ, or intranasal
Typical dose
0.5–1 mg daily
Frequency
Once daily
Half-life
Not established in humans.
Cycle
4–8 weeks, then a break.
Vial sizes sold
10mg or 5mg
These are the numbers people actually run, drawn from the published record and from what the community has settled on over time. Educational reference, not medical advice — a starting point to work from, and one you can adjust as you learn how you respond.

How to run it

How often
Once daily
Cycle length
4–8 weeks, then a break.
Half-life
Not established in humans.
Route
SubQ, or intranasal
Consistency matters more than perfect timing. Pick a slot in your day you will actually keep, and let DoseIQ handle the rest.

What people actually run

Often paired with Semax or Dihexa. Reported as subtler than either, with effects that build over weeks rather than being felt acutely.

This is accumulated community practice — years of real-world use across a large number of people, converging on numbers that work. It is not a controlled trial, and for most compounds here no such trial exists or is ever likely to. That makes this the most reliable dosing signal available, and it is a good deal better than guessing.

What to expect

Most people tolerate P21 well. Here is what is worth knowing going in, so nothing catches you by surprise.

Animal data only, and no human safety characterisation at all. Well tolerated in the community record so far, though that record is short. Effects are described as gradual, so give it weeks before judging rather than escalating the dose.

Reconstitution guide

P21 ships as a lyophilised powder and gets mixed with bacteriostatic water before use. How much water you add sets the concentration, which sets how many syringe units make up each dose. One unit on a U-100 syringe is 0.01 mL — the tables below do the arithmetic for the vial sizes you are most likely to be holding.

10mg vial most common

Water addedConcentration 0.5mg1mg
2mL (common) 5 mg/mL0.10 mL
10 units		0.20 mL
20 units
3mL 3.33 mg/mL0.15 mL
15 units		0.30 mL
30 units

5mg vial

Water addedConcentration 0.5mg1mg
2mL (common) 2.5 mg/mL0.20 mL
20 units		0.40 mL
40 units
3mL 1.67 mg/mL0.30 mL
30 units		0.60 mL
60 units
10 mg vial + 1 mL BAC water = 10 mg/mL — a 1 mg dose = 10 units on a U-100 syringe. 5 mg vial + 1 mL = 5 mg/mL — 1 mg = 20 units.

Standard steps

  1. Inspect the vialConfirm the label and that the powder cake is intact. Do not use a cracked or compromised vial.
  2. Let it reach room temperatureSitting out for a few minutes reduces condensation inside the vial when the seal is broken.
  3. Disinfect both stoppersWipe the compound vial and the bacteriostatic water vial with a fresh alcohol swab and let them air-dry.
  4. Draw the bacteriostatic waterUse a sterile syringe to draw the volume you have chosen from the reconstitution table.
  5. Add the water down the vial wallInject slowly so it runs down the inside wall rather than spraying directly onto the powder. This limits foaming.
  6. Dissolve gentlySwirl or roll the vial between your hands until the cake dissolves. Never shake — agitation damages peptide bonds. The solution should end up clear.
  7. Label and refrigerateWrite the reconstitution date and concentration on the vial. Store at 2–8°C. Do not freeze.
Running a different vial size or water volume? The DoseIQ calculator works it out for any combination — mcg, mg or IU, on any syringe size.
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This page is an educational research reference and is not medical advice. P21 is not approved for human use in any jurisdiction. Dose figures reflect the published record and what the community has converged on — starting points to weigh, not instructions. Consult a qualified healthcare provider before starting any protocol.