Caffeine vs Ashwagandha
for cognition
Stronger evidence: Caffeine
Stronger effect: Caffeine
Safety: Ashwagandha has the more serious interaction profile (minor vs moderate).
For cognition, Caffeine has the stronger evidence grade.
Caffeine
grade A high certainty
reliably improves alertness, reaction time, and vigilance
40–200 mg, adults
Ashwagandha
grade C low certainty
preliminary improvements in memory/executive function; small trials
300–600 mg/day, adults
sources: PMID:00000020 · PMID:42220661