Caffeine for Cognitive Function
Caffeine reliably gives a small-to-moderate acute lift to alertness, attention, and reaction speed, but evidence for lasting memory or dementia-prevention benefits is weak. It is graded Preliminary (Tier B) Evidence.
Why this grade7-layer evidence engine
This is a Tier B (Preliminary Evidence) verdict because the proven benefit is narrow and the effect is modest rather than large. Two meta-analyses point the same direction: a 2025 high-quality pooled analysis (PMID 40335666, n=1,455) found acute caffeine significantly improved attention accuracy and reaction time, though the effect sizes were small (Hedges' g around 0.27-0.28), with doses of 200mg or more working best. A 2021 sports-focused meta-analysis (PMID 33800853) similarly reported gains in attention, accuracy, and speed.
The supporting trials are small and mostly in young, physically active people, which caps the grade. One double-blind RCT (PMID 39231871, n=29) saw faster reaction times only at the higher 6 mg/kg dose, not at 3 mg/kg, and another (PMID 40581775, n=13) showed only brainwave (P300) changes in a tiny fatigued-athlete sample. Notably, the 2025 meta-analysis found the benefit did not depend on habitual intake, which weakens the argument that caffeine merely reverses withdrawal.
Authorities are broadly consistent but cautious about overreach. Mayo Clinic agrees moderate caffeine improves alertness, reaction time, and processing speed; the FDA classes it as generally recognized as safe, and EFSA considers up to 200mg per dose (400mg/day) safe for healthy adults. However, 'cognitive function' is an umbrella term: evidence for long-term memory, executive function, and dementia prevention is thin and largely observational. Caffeine also carries safety caveats, including a drug interaction with fluvoxamine that can cause caffeine intoxication (PMID 8807660).
Scoring transparency
All scores computed by a 7-layer evidence engine — fully auditable▸View the full decision path (audit trail)
- compute_raw_score — 加權公式: L2×0.30 + L3×0.25 + L5×0.25 + L11×0.10 + L1×0.10 = 0.65
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高品質 SR/MA 顯示 positive (1 篇 > 0 negative)
- tier_strict_requirement_check — Tier 條件達標，未降階
- detect_disputes — 偵測到 0 個 hard + 0 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status