Topic
Brain & Cognitive Health
Quick answers
- What is it?
- This hub covers what controlled human research says about brain function and mental sharpness — from everyday habits like caffeine, creatine, omega-3s, and exercise, to research peptides like Cerebrolysin, Semax, Selank, and MK-677, plus the question of whether "brain fog" is a real, measurable thing.
- Why are people interested in it?
- People want sharper focus, better memory, and less mental fatigue, and there's a large and growing market of supplements, peptides, and lifestyle advice promising exactly that — so it matters which of these claims actually hold up in controlled human trials versus which are riding on marketing and anecdote.
- What has actually been studied?
- The sources cover randomized controlled trials and meta-analyses of caffeine, creatine, omega-3 fatty acids, and exercise in healthy adults and older adults; racetams and other "nootropics" mostly in dementia or cognitively impaired patients; Cerebrolysin (a porcine-brain-derived peptide) across 42 registered trials in stroke, dementia, and other conditions; Semax and Selank (Russian synthetic peptides) in small, mostly unblinded studies; MK-677 (a growth hormone secretagogue) in older adults, Alzheimer's disease, and other conditions; and "brain fog" across long COVID, celiac disease, PTSD, and hypersomnia.
- How strong is the evidence?
- It varies enormously by compound: caffeine's benefit under real sleep deprivation is well established but its everyday "boost" is disputed between two conflicting controlled trials; creatine helps memory more reliably in older adults than in young adults; the largest omega-3 trials (over 12,000 combined participants) found no cognitive benefit; exercise has a large, well-established effect on mood but only a small, often non-significant effect on cognition; racetam evidence is decades old, drawn mostly from dementia patients, and piracetam actually worsened symptoms in one dementia population; Cerebrolysin has large real trials but manufacturer-linked and independent Cochrane reviews reach opposite conclusions; and Semax/Selank evidence is almost entirely small, unblinded studies from Russia with zero trials registered on ClinicalTrials.gov.
- What don't we know yet?
- Across these sources, it's largely unknown whether these interventions do anything measurable for healthy, non-impaired people specifically (most large trials studied older adults or diagnosed patients); whether "brain fog" reflects one shared mechanism or several unrelated ones; whether Semax, Selank, or Cerebrolysin's Russian- or manufacturer-linked findings would replicate in independent, placebo-controlled trials; and the long-term effects of continuous use for nearly every compound covered.
- Where can I read the original research?
- Explore the individual articles and peptide profiles in this hub for the specific trial numbers, study populations, and sourced quotes behind each of these findings.
Semax, Selank and Cerebrolysin have a substantial research literature, but much of it comes from a single country, in small trials, and has not been replicated elsewhere. This hub covers those compounds along with the mainstream questions about cognition: exercise, omega-3, creatine and what the evidence actually measures.
Peptides in the Evidence Index
Research on this topic
Video briefs
Frequently asked
Is "brain fog" a real, measurable thing?
"Brain fog" has no formal diagnosis, no ICD or DSM code, and no single validated test — researchers borrow the term patients use and then measure whatever they can. Under that umbrella, real signal does turn up: a meta-analysis of 81 studies and 13,232 people found 22% reported cognitive impairment 12 or more weeks after COVID-19, while a narrower analysis using the term "brain fog" specifically, across 19 studies and 11,324 patients, put the figure at 32% but with a confidence interval spanning 9% to 55%. In several conditions, such as HIV and functional cognitive disorder, what people report about their own thinking and what they score on objective tests frequently diverge, in both directions. The complaint is consistently real; what it's tracking is still contested.
What has Cerebrolysin actually been tested for, and did it work?
Cerebrolysin, a porcine-brain-derived peptide mixture, has the largest clinical-trial footprint of any compound in this hub — 42 registered trials spanning stroke, vascular dementia, Alzheimer's disease, traumatic brain injury, and more. The results are genuinely contested: the largest trial (CASTA, 1,070 acute stroke patients) found no significant difference from placebo on its primary endpoint, and independent Cochrane reviews found it "probably has little or no beneficial effect" on death after stroke while flagging a potential increase in non-fatal serious adverse events — but separate meta-analyses, some with manufacturer-linked authors, reported significant cognitive and functional benefits. One small pilot trial did find a clear benefit for post-stroke language recovery, but it hasn't been replicated at larger scale.
Is there human evidence for Semax and Selank outside Russia?
Barely any. A ClinicalTrials.gov search found zero registered trials for either peptide under any spelling, and the human literature for both is small and almost entirely Russian: a 2007 open-label study tested Semax in 27 motor neuron disease patients, and a 2008 trial compared Selank to the benzodiazepine medazepam (not placebo) in 62 anxiety patients. A 2026 review of these "neuroactive peptides" concluded there is "a current lack of clinical trials," and no independent research group outside Russia appears to have run a controlled trial of either compound.
Do racetams and other "nootropics" actually work?
The evidence is older, thinner, and more mixed than "smart drug" marketing implies, and most of it comes from dementia patients rather than healthy people. A 2002 meta-analysis of 19 trials found piracetam produced a favorable global impression of change in people with dementia or cognitive impairment, but a 2023 network meta-analysis found it significantly worsened neuropsychiatric symptoms in frontotemporal dementia, and a 2015 review concluded it doesn't appear effective for Lewy body dementia. In healthy volunteers specifically, one small 1990 trial found aniracetam — not piracetam — reversed drug-induced memory impairment, and a 2022 pharmacology review concluded any benefit in healthy, non-impaired people remains uncertain and, when reported, temporary.
Does creatine do anything for the brain?
It depends heavily on who's taking it. A 2023 meta-analysis of eight randomized trials found creatine improved memory overall, but the effect was large in adults aged 66-76 and close to zero in adults aged 11-31. The largest single trial to date (123 adults) found only a borderline effect on working memory and no effect on fluid intelligence, with more side effects reported on creatine than placebo. A smaller trial in perimenopausal and menopausal women found a medium dose improved reaction time and raised frontal-lobe brain creatine, while a trial in healthy 10- to 12-year-olds found a week of supplementation changed neither brain creatine nor test scores.
Does caffeine actually improve cognitive performance?
Under real sleep deprivation and stress, yes — a trial in 68 Navy SEAL trainees after 72 hours without sleep found 200-300 mg of caffeine significantly improved vigilance, reaction time, and learning in a dose-dependent way. But in everyday, non-extreme settings, a substantial share of the "boost" looks like withdrawal reversal rather than true enhancement: one controlled trial found caffeine improved mood and performance only in habitual coffee drinkers who'd gone without it overnight, while a separate, similarly designed trial found benefits in both habitual users and non-consumers, so the two studies directly disagree. A 2010 Cochrane review of 13 trials found caffeine improved memory, attention, and perception scores, but had no effect on verbal functioning and language skills.
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