Ingredient Evidence Review
L-theanine
L-theanine (from green tea)
Last updated 2026-05-19 · 3 primary citations
Mechanism
L-theanine is the amino acid in green tea that makes a green-tea caffeine boost feel calm rather than jittery. It produces alpha-wave brain activity (the same pattern as relaxed focus and meditation) and softens caffeine's edge without blunting its alertness benefit.
Why we use it
If caffeine alone is a sharp spike, theanine is what makes it a smooth ride. Without it, the AM stick would have the same crash profile as the energy drinks shift workers want to escape.
How we dose it
Hericea uses 200 mg per serving (per On-Shift stick pack). The clinical trial range that anchors this dose is 100–400 mg/day.
200 mg of Suntheanine®, the pure form of L-theanine — about ten cups of green tea worth. Paired with 100 mg of caffeine at the 2:1 ratio that the foundational trials used.
Quality & sourcing
Suntheanine® ≥99% L-isomer.
Taiyo International-licensed Suntheanine®.
Primary literature
Haskell CF et al. (2008)
Biol PsycholRCT
L-theanine 250 mg + caffeine 150 mg improved cognitive performance and increased alertness more than caffeine alone.
The single most-cited trial for the caffeine + theanine pairing — established the smooth-focus profile.
PMID 18006208
Giesbrecht T et al. (2010)
Nutr NeurosciRCT
L-theanine + caffeine improved cognitive flexibility (task-switching) compared to placebo.
Task-switching is the specific cognitive demand shift workers face when handing off between systems.
PMID 21040626
Williams JL et al. (2020)
Plant Foods Hum NutrReview
Reviewed L-theanine effects on stress, sleep, and cognitive performance.
Single source for the broader theanine evidence base beyond the caffeine pairing.
PMID 31758301