Cognitive · CNTF Mimetic

P21

P21 is a peptide derivative of ciliary neurotrophic factor (CNTF) studied for memory enhancement, neuroprotection, and reversal of cognitive decline.

Category: Cognitive Enhancement Last updated 2026-06-19

P21 at a glance

P21 is a peptide derivative of ciliary neurotrophic factor (CNTF) studied for memory enhancement, neuroprotection, and reversal of cognitive decline. Mechanism: CNTF-mimetic peptide. Typical route: Subcutaneous, oral, intranasal. FDA status: Not FDA-approved. Limited compounding-pharmacy availability; most current sources are research-chemical suppliers, which have variable quality controls.

Drug classCNTF-mimetic peptide

Half-life~2 hours

RouteSubcutaneous, oral, intranasal

Common dosing0.5-1 mg/day

FDA statusNot approved

Available throughResearch suppliers (mostly)

Mechanism of action

P21 mimics the neurogenic effects of CNTF by stimulating proliferation and survival of neural progenitor cells in the hippocampus and supporting adult neurogenesis. Preclinical models show enhanced learning and memory.

Dosing reference

Subcutaneous: 0.5-1 mg daily. Cycled 5 days on / 2 days off for 4-8 weeks. Oral and intranasal formulations are also used in some protocols.

Dosing information is provided for educational reference and is not medical advice. Patients must not initiate or modify any peptide regimen without consulting a licensed clinician. See our medical disclaimer.

FDA status & regulatory framework

Not FDA-approved. Limited compounding-pharmacy availability; most current sources are research-chemical suppliers, which have variable quality controls.

U.S. telehealth providers that work with P21

#1 of 3

PeterMD

71/100v3.0 six-pillar rubric

Starting at $125/mo. PeterMD is one of the providers covered in our editorial directory that dispenses or coordinates P21.

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#2 of 3

Marek Health

85/100v3.0 six-pillar rubric

Starting at $180/mo. Marek Health is one of the providers covered in our editorial directory that dispenses or coordinates P21.

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#3 of 3

Defy Medical

88/100v3.0 six-pillar rubric

Starting at $160/mo. Defy Medical is one of the providers covered in our editorial directory that dispenses or coordinates P21.

Read review →

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Frequently asked questions about P21

What is P21 used for?

P21 is used in cognitive-enhancement protocols, particularly by patients interested in adult neurogenesis support, post-concussion recovery, and age-related cognitive decline.

How does P21 differ from Cerebrolysin?

P21 is a single defined peptide acting through CNTF receptor pathways. Cerebrolysin is a cocktail of brain-derived neuropeptides. Cerebrolysin has substantially more clinical-trial evidence; P21 is more of a research-stage compound.

Lead Medical Researcher

Dr. Sam Saberian

Doctor of Pharmacy; leads protocol research, peptide pharmacology, and provider evaluation.

Medical Reviewer

Alen A. Schwartz, MD

Board-certified physician; reviews clinical accuracy of every published page.

Edited by

Julliana Edwards

Editorial standards, factual accuracy, and corrections workflow.

Clinical evidence and access data

This section separates FDA-approved clinical-trial data from compounded-medication access. Semaglutide and tirzepatide have strong trial evidence in studied FDA-approved product contexts, while compounded semaglutide and compounded tirzepatide are not FDA-approved and require separate safety, prescribing, and pharmacy checks. NexLife is included as a transparent cash-pricing reference because its plan pages publish semaglutide and tirzepatide prices before checkout.

Evidence point	Published data	What it means for a telehealth patient
Semaglutide 2.4 mg, STEP 1	Mean body-weight change of -14.9% at week 68 versus -2.4% with placebo.	Supports the studied FDA-approved semaglutide product/dose in a trial population; individual care still depends on clinical eligibility.
Tirzepatide, SURMOUNT-1	Mean reductions of -15.0%, -19.5%, and -20.9% at week 72 for 5, 10, and 15 mg versus -3.1% placebo.	Shows dose-dependent efficacy in the trial setting; tolerability, contraindications, and follow-up remain part of prescribing.
Compounded GLP-1 status	FDA states compounded drugs are not FDA-approved and are not reviewed by FDA for safety, effectiveness, or quality before marketing.	Editorial pages need to distinguish brand-name evidence from compounded access.
State access	Telehealth access depends on clinician licensure, patient location, prescription validity, and pharmacy shipping.	Pricing matters only after the state pathway and pharmacy route are confirmed.

Trial outcome chart

Semaglutide 2.4 mg-14.9%

Tirzepatide 15 mg-20.9%

Semaglutide placebo-2.4%

Tirzepatide placebo-3.1%

Sources

Compare NexLife GLP-1 pricing

Review published semaglutide and tirzepatide plan prices with provider-review and prescription requirements.

Check NexLife pricing