Caffeine
The most-used stimulant on earth, and one of the few supplements with strong evidence for both cognitive and physical performance.
100-400 mg
A Strong human evidenceNootropicsPerformance
Nootropics · Sleep
L-Theanine
Also known as: theanine, N-ethyl-L-glutamine
The amino acid in green tea that takes the edge off stress — and off caffeine — without sedation.
Grade BGood human evidence
Studied dose100-400 mg
TimingWith your coffee for the pairing effect…
EvidenceGrade B
CategoryNootropics
Consistent placebo-controlled trials show reduced subjective stress and improved attention when combined with caffeine. Trials are numerous but mostly small and short.
L-theanine is the reason a cup of green tea feels different from a cup of coffee with the same caffeine. It is an amino acid nearly unique to tea leaves, and its signature effect is what researchers call relaxed alertness: alpha-brain-wave activity rises, subjective stress drops, and none of it comes with drowsiness or impaired performance.
The best-replicated use is the caffeine pairing. Multiple placebo-controlled trials of caffeine plus theanine — typically 100-200 mg of each — show improved attention-switching and reduced susceptibility to distraction compared with caffeine alone, alongside less jitter and a smaller blood-pressure bump. If caffeine gives you the output but also the edge, this is the cheapest fix with actual evidence behind it.
On its own, theanine’s case is solid but narrower. Randomized trials in adults under stress show reductions in subjective anxiety and stress-marker responses at 200-400 mg. The sleep evidence is thinner: theanine does not knock you out the way melatonin shifts your clock, but by quieting pre-sleep arousal it can shorten the wind-down, and small trials in adults and in children with ADHD report better subjective sleep quality.
The safety profile is about as clean as supplements get. No meaningful side effects have surfaced at studied doses, tolerance does not appear to build, and there is no withdrawal. That cleanliness is part of why it is popular — but keep the claim honest: theanine polishes the experience of being alert or winding down; it does not add horsepower on its own. Treat it as a modifier, best used to make caffeine more usable or evenings less wired.
How it works
L-theanine crosses the blood-brain barrier and increases alpha-wave activity associated with relaxed alertness. It modulates glutamate signaling and raises GABA, serotonin, and dopamine levels modestly — enough to blunt the sympathetic stress response without acting as a sedative.
What the evidence supports
- Improves attention when paired with caffeine B
- Reduces subjective stress and anxiety 200-400 mg in acute-stress trialsB
- Improves sleep quality via reduced pre-sleep arousal, not sedationC
Safety
Exceptionally well tolerated at studied doses with no established toxicity, no tolerance build-up, and no withdrawal. Generally recognized as safe as a tea constituent consumed for centuries.
Reported side effects
- Occasional mild headache
- Drowsiness at very high doses in sensitive users
This guide is educational, not medical advice. Talk to a physician or pharmacist before starting any supplement, especially alongside prescription medication or a medical condition.
Common questions
- What does L-Theanine do?
- The amino acid in green tea that takes the edge off stress — and off caffeine — without sedation. Its best-supported effects are improves attention when paired with caffeine and reduces subjective stress and anxiety.
- Does L-Theanine actually work?
- Good human evidence (grade B). Consistent placebo-controlled trials show reduced subjective stress and improved attention when combined with caffeine. Trials are numerous but mostly small and short.
- How much L-Theanine should I take?
- The studied range is 100-400 mg, once daily; 100-200 mg alongside caffeine is the studied pairing. Start at the low end — more is not better once the effective range is covered.
- When should I take L-Theanine?
- With your coffee for the pairing effect, or 30-60 minutes before bed for relaxation. It does not sedate, so daytime use is fine.
- Is L-Theanine safe?
- Exceptionally well tolerated at studied doses with no established toxicity, no tolerance build-up, and no withdrawal. Generally recognized as safe as a tea constituent consumed for centuries. The most reported side effects are occasional mild headache, drowsiness at very high doses in sensitive users.
References
Evidence review last updated
- Haskell, C. F., et al. (2008). "The effects of L-theanine, caffeine and their combination on cognition and mood." Biological Psychology. Source
- Hidese, S., et al. (2019). "Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults: a randomized controlled trial." Nutrients. Source