# P21 (P021)

CNTF-derived neurogenic peptide from Alzheimer's mouse work; grey market only.

- Page: https://peprank.xyz/peptides/p21
- Category: Neuroprotection & repair (Research peptide)
- Also known as: Peptide 021; adamantylated CNTF-derived tetrapeptide
- Routes: Nasal / Oral / Injection
- Sequence: DGGL (P021: Ac-Asp-Gly-Gly-Leu-adamantylglycine-NH2 (non-standard C-terminal residue); CNTF-derived)
- Safety tier: Strict: Caution · Balanced: Caution · Evidence only: Caution
- Risk axes (0 none to 3 severe): Seen harm 1, Mechanism 1, Data gap 3, Silent harm 1, Product 2
- Positive: 43% of 15 graded reports glowing or positive, shrunk toward the 49% all-report average by 8 reports' weight
- Rank: #21 of 61 research peptides
- Graded reports: 15 (Positive 6, Mixed 4, Negative 3, Bad reaction 2)
- Evidence: Animal only
- Access: Grey market
- Onset: Users split: some feel nasal stimulation or a mood shift within 20-60 minutes (one had a panic attack seconds after a subq dose); others feel little for one to several weeks. The rodent neurogenesis effects take weeks.
- Lasts: Acute stimulation lasts a few hours per nasal dose; tolerance to it builds within weeks, and several users escalated from 1 mg to 3-4 mg a day.
- Cost per month: ≈ €45–180 (researchers' estimate)
- Updated: 2026-10-30

**Why Avoid under the strict bar:** No human safety data; deliberately drives neurogenesis via a growth-factor pathway, and products are of uncertain identity.

## What users report

Sparse (under 20 first-hand Reddit reports), about half positive: more stamina for studying, presence and less anxiety, TBI recovery, usually rated below genuine Cerebrolysin. Others report panic on injection, nightmares, sleepiness, anger, lingering head heat, tinnitus or mild hair shedding, and tolerance comes fast. One unverified user describes near-blindness (suppressed cone responses on mfERG) after 7.5 months of nasal use. Few report outright nothing, though many call it subtle; vendor identity confusion is common.

**Effects:** study stamina/persistence; being 'in the moment', less overthinking; mild stimulation

**Downsides:** acute panic/anxiety after injection; head warmth, tinnitus; irritability/anger; mild hair shedding; rapid tolerance

**Risks:** no human data of any kind; neurogenic/neurotrophic (CNTF/LIF pathway) effects with unknown long-term consequences; grey-market identity unclear (with or without adamantane)

**Typical use:** 500 mcg-1 mg/day nasal or subq (community, wide range).

**Getting it:** Research-peptide vendors only (first Ceretropic and its Mexican reseller, now Chinese suppliers and 'research use' shops). Products disagree on whether the adamantane group is present, and at least one vendor admitted its P21 was not the real sequence.

**Stacked with:** Semax (Users combine them in one syringe or spray and describe the mix as more stimulating than either alone.); Cerebrolysin (Often run alongside or instead of it; several users who tried both preferred genuine Cerebrolysin.); PE-22-28 (One user who took both became uncharacteristically angry.)

## Risk profile

- **Seen harm 1/3:** No human study exists. One first-hand report describes near-blindness with suppressed cone responses on electroretinography after 7.5 months of nasal use, unresolved after a year, from a vendor of uncertain identity; isolated and unverified.
- **Mechanism 1/3:** A CNTF-derived peptidomimetic built to raise BDNF and neurogenesis without CNTF's gp130 signalling, the source of full CNTF's anorexia and muscle loss; up to 18 months of rodent dosing caused no tumours or weight loss, so the concern is speculative.
- **Data gap 3/3:** No human data of any kind, and vendors disagree on whether the adamantane group is present.
- **Silent harm 1/3:** Reported effects (panic, head heat, tinnitus) are felt within days, though the isolated visual report developed over months.
- **Product 2/3:** Grey-market nasal sprays, capsules or vials, with the molecule's identity disputed between vendors.
- **Never if:** Pregnancy or breastfeeding (no human reproductive data)

## Top reports

- Positive, mood: “P21 is a mystery peptide, but based on my experience of continuous use, it seems to somewhat relieve depressive symptoms.” — [r/Biohackers](https://www.reddit.com/r/Biohackers/comments/yebanp/best_peptides_to_heal_my_brain/ityigmj/)
- Positive, focus: “I've used P21 and Adamax, would rate both a 7/10, Cerebro/Cortex as close to 10 as anything I've tried.” — [r/NooTopics](https://www.reddit.com/r/NooTopics/comments/122s1ld/the_trinity_p21_adamax_and_adalank/jdt2xht/)
- Positive, anxiety: “Less anxiety, more "in the moment" instead of overthinking, more relaxed in social situations, i think more focused too.” — [r/NooTopics](https://www.reddit.com/r/NooTopics/comments/11q3hid/p21/jc3yiwn/)
- Positive, neuroprotection: “P21 rocks but if you have serious issues you will need a lot of it. It makes my hair fall out too a little. For me it’s worth it but ymmv.” — [r/Cerebrolysin](https://www.reddit.com/r/Cerebrolysin/comments/1gkueex/what_is_your_experience_with_p21_nasal_sprays/lvutuvq/)
- Positive, recovery: “Semax didn't do anything for me. P21 knocked my tbi back to where it belongs. I stayed on it for too long though.” — [r/Peptidesource](https://www.reddit.com/r/Peptidesource/comments/1f2ravb/is_anyone_of_you_combining_p21_with_semax_or/llk7lx5/)

## Studies

- [Li et al. 2010: neurotrophic peptides incorporating adamantane improve learning and memory, promote neurogenesis and synaptic plasticity in mice](https://pubmed.ncbi.nlm.nih.gov/20600002/) (animal, 2010): The paper that introduced P21 (Ac-DGGLAG-NH2); given peripherally it improved learning and short-term and spatial memory in normal adult mice and increased dentate-gyrus neurogenesis.
- [Kazim et al. 2014: disease-modifying effect of chronic oral P021 in a triple-transgenic mouse model of Alzheimer's disease](https://pubmed.ncbi.nlm.nih.gov/25046994/) (animal, 2014): Twelve months of P021 in the diet reduced tau hyperphosphorylation and soluble amyloid-beta and rescued cognition, neurogenesis and synaptic plasticity in 3xTg-AD mice, apparently through raised BDNF and lower GSK-3beta activity.
- [Khatoon et al. 2015: elevated tau in aged rat cerebrospinal fluid reduced by treatment with a neurotrophic compound](https://pubmed.ncbi.nlm.nih.gov/26401692/) (animal, 2015): Oral P021 crossed the blood-brain barrier and brought brain and CSF tau in aged rats down to young-adult levels, with no detectable immune reaction.
- [Baazaoui & Iqbal 2017: prevention of amyloid-beta and tau pathologies, neurodegeneration and cognitive deficit by early treatment with a neurotrophic compound](https://pubmed.ncbi.nlm.nih.gov/28387677/) (animal, 2017): Starting P021 before pathology appeared prevented amyloid and tau build-up, neuron loss and memory deficits in 3xTg-AD mice.
- [Wei et al. 2021: neurotrophic treatment initiated during early postnatal development prevents Alzheimer-like behaviour and synaptic dysfunction](https://pubmed.ncbi.nlm.nih.gov/34057082/) (animal, 2021): P021 given from the early postnatal period prevented later Alzheimer-like behaviour and synaptic deficits in transgenic mice. No study in humans exists.

## Sources

- [Kazim et al. 2014: chronic oral P021 in 3xTg-AD mice](https://pubmed.ncbi.nlm.nih.gov/25046994/)
- [Baazaoui & Iqbal 2017: prevention of synaptic deficits with P021](https://pmc.ncbi.nlm.nih.gov/articles/PMC5488423/)