What to take for cognition

Graded by the strength of the evidence — strongest first. Nothing here is sold to you.

Caffeinegrade A— reliably improves alertness, reaction time, and vigilance

Creatinegrade B— Meta-analysis of 16 RCTs (n≈492 adults): improved memory, attention, and processing speed; no significant effect on overall or executive function.

Melatoningrade B— Meta-analysis of RCTs in older adults with cognitive impairment: melatonin produced a modest improvement in cognition (MMSE +1.8 points) and total sleep time (+12.4 minutes), with a small reduction in neuropsychiatric symptoms. The authors conclude effects approach — but fall short of — definitive clinical efficacy, with substantial heterogeneity between trials.

Lion's Manegrade C— early, small studies suggest a modest cognitive effect

Ginkgograde C— no reliable benefit for preventing cognitive decline in large trials

L-Theaninegrade C— improves attention and cuts down distraction, especially paired with caffeine

Irongrade C— improves attention/cognition when iron deficiency is present; no benefit if replete

Ashwagandhagrade C— preliminary improvements in memory/executive function; small trials

Vitamin Dgrade C— Systematic review and meta-analysis: lower vitamin D levels are associated with poorer cognition and higher dementia risk. The association is mostly observational; supplementation trials have not established that raising vitamin D improves cognition.

Turmericgrade C— Systematic review: curcumin may modestly benefit some cognitive domains in older adults, but effects are inconsistent across domains and trials are small, with bioavailability a recurring limitation.

Rhodiolagrade C— Review of Rhodiola rosea preparations: modest reductions in mental fatigue and small improvements in cognitive performance under stress in some trials. Studies are small and of low-to-moderate quality.

Magnesiumgrade C— Systematic review of magnesium and cognitive health in adults: the evidence linking magnesium status or intake to cognition is limited and inconsistent, drawn largely from observational data, and the authors call for better-designed studies with repeated magnesium biomarkers before any conclusion. No demonstrated cognitive benefit from supplementation.

Caffeinegrade D— Cochrane review, 13 RCTs, shift-work context: memory/attention improved, no verbal-skill benefit; high risk of bias flagged; mostly young people in simulated conditions, not real shift workers.