People mainly take P21 for focus, memory, energy. Based on 28 first-hand reports and 271 meta-analyses & systematic reviews in the medical literature. Ranked #554 of 1,974 overall.
Of reports that state an outcome, 55% are positive.
Of the people who reported each effect, the share who said it got better.
Systematic reviews and meta-analyses from PubMed, with their published conclusions.
3+ meta-analyses or systematic reviews and 10+ randomized controlled trials in humans. The grade measures how much human research exists — read the conclusions below for what it found.
Conclusion: Comprehensive meta-analysis indicates a higher prevalence and incidence of BM in patients with certain targetable genomic alterations. This supports brain imaging at staging and follow-up, and the need for targeted therapies with brain penetrance.
PubMed 37392903 ↗Conclusion: Among the ALL subtypes, positive predictive values of greater than 0.8 were reached only for the L3-associated aberrations t(2;8) (1.0), t(8;14) (0.95), t(8;22) (0.87), and dup(I) (0.80). The highest negative predictive values were in AML 0.98 that the disease is not M3 if t(15;17) is not found, and in ALL 0.96 that the patient does not have L3 if a t(8;14) is not detected.
PubMed 1384663 ↗Conclusion: Mendelian randomisation analysis supports causal roles for several HF risk factors, and demonstrates CAD-independent effects for atrial fibrillation, body mass index, and hypertension. These findings extend our knowledge of the pathways underlying HF and may inform new therapeutic strategies.
PubMed 31919418 ↗Conclusion: This is the first investigation of cancer risk in KRAS or HRAS PV-positive mosaic RASopathies to date. The high incidence and SIR values found highlight the need for rigorous RMS surveillance in young children and skin cancer surveillance in adults with this high-risk condition.
PubMed 39287844 ↗As stated by users — not a recommendation. Follow the label or your doctor.
How often each side effect came up across all reports.
Verbatim quotes, shortened only — each links to the original discussion.
“P21”
“I'll have to check out P21, BPC-157, and Cerebrolysin.”
“There's P21 a synthetic equivalent which can be pinned subcutaneously but it has far less research on it.”
“It made me very talkative and focused. It also made me a little tired after a while.”
“after injecting 2mg SID for a week something is happening... P21 seems to significantly enhance my memory and linguistic abilities while incorporating a subtle, gradual mood lift”
User data from public discussions; research from PubMed. Information only, not medical advice — talk to a doctor before starting, stopping or combining anything. Data updated October 2, 2026. How we rate