L-Theanine + caffeine (cognitive stack)

Tier 2 — promising · Focus · Alertness · No jitters · 2:1 ratio · Studied combination

The most rigorously studied natural cognitive combination. At a 2:1 ratio (200 mg L-theanine + 100 mg caffeine), multiple RCTs demonstrate superior improvements in sustained attention, reaction time, and accuracy versus either compound alone. Haskell 2007 (PMID 18006208, crossover RCT) and Giesbrecht 2010 (PMID 21040626, n=44 RCT) both confirm improved accuracy in demanding tasks and reduced self-reported fatigue. L-theanine promotes alpha-wave activity and attenuates caffeine-induced jitteriness and anxiety while preserving alertness. A 2017 review of 49 intervention studies (Dietz, PMID…

Dose: 200 mg L-theanine + 100 mg caffeine taken simultaneously; or with morning coffee. Avoid after 2 pm to protect sleep.