Caffeine + L-theanine
What it is
Caffeine blocks adenosine receptors for alertness; L-theanine (an amino acid in tea) increases alpha brain-wave activity and blunts caffeine's jitteriness.
What the evidence says
This is the best-supported combo here. A 2014 Nutrition Reviews systematic review and meta-analysis of 11 placebo-controlled trials found moderate-sized benefits favoring caffeine plus L-theanine for alertness and attention-switching accuracy within the first ~2 hours post-dose, with caffeine driving most of the effect. Benefits are acute (not lasting cognitive enhancement), and individual trials are small and heterogeneous. L-theanine appears to attenuate caffeine-induced blood-pressure rise without blunting the alertness benefit.
Roughly 50-100 mg caffeine paired with 100-200 mg L-theanine (about a 1:2 ratio) per dose, as used in most trials.
Educational summary of doses studied — not a recommendation. Talk to a clinician before starting any supplement.
Sources (1)
- Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis — Nutrition Reviews (PMID: 24946991) (2014)
Educational summary of published research, checked against primary sources and linked inline. Not medical advice; supplements are not FDA-evaluated to treat disease. See our editorial policy.