Caffeine + L-Theanine

The best-documented nootropic stack there is: coffee's focus without the jitter tax.

Overall grade: Grade B
Last revised: Jun 12, 2026; 4
graded outcomes: 3
references listed

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A hand-written entry in Prometheus's bundled library. Its grades are the entry's own reading of the evidence, not a peer-reviewed review.

2 at grade A · 3 at grade B · 3 at grade C — 8 graded rows

What is known

Each outcome with its grade (how strong the evidence is, A to D), the size of the effect where the entry records one, and how often studies agree.

Outcome	Grade	Effect size	Agreement
Reaction timeCaffeine-driven, dose 3–6 mg/kg	Evidence grade A	Small	high
Sleep harm from late dosingDeep-sleep reduction with <8h between dose and bed	Evidence grade A	Large	high
Sustained attentionCombo beats either compound alone in switching tasks	Evidence grade B	Moderate	high
Jitter / anxiety reduction vs caffeine aloneTheanine's main contribution	Evidence grade B	Moderate	high

Reaction timeEvidence grade A
Caffeine-driven, dose 3–6 mg/kg
Smallhigh
Sleep harm from late dosingEvidence grade A
Deep-sleep reduction with <8h between dose and bed
Largehigh
Sustained attentionEvidence grade B
Combo beats either compound alone in switching tasks
Moderatehigh
Jitter / anxiety reduction vs caffeine aloneEvidence grade B
Theanine's main contribution
Moderatehigh

Conditions

How the entry reads its effect on diagnosed conditions: the direction first, then the grade. Never a substitute for the person who treats you.

ADHD (adult) May improveEvidence grade CSmall attention gains; not a substitute for treatmentGrade C
Anxiety disorders May worsenEvidence grade BCaffeine is anxiogenic at higher doses; theanine only partly offsetsGrade B
Hypertension May worsenEvidence grade CAcute BP bump in naive users; tolerance develops with regular useGrade C
Migraine May improveEvidence grade CAcute adjunct at onset; chronic overuse triggers rebound headachesGrade C

What is uncertain

Read off the same rows as above. Nothing here is added that the entry does not itself record.

Watch with Sleep architecture: Late dosing is the single most common self-inflicted sleep wound

100mg dose still circulating · time course

Up: mg circulating. Across: hours after dose. The half-life is the whole story: a 16:00 espresso is a midnight problem. Cut off 8–10h before bed.

The evidence in words

Why the pair works

Caffeine blocks adenosine (alertness, faster reaction time, more error-proneness under load); theanine raises alpha-wave activity and takes the edge off the sympathetic spike. Combined trials show attention-switching and accuracy improvements the single compounds don't match.

The half-life problem

Caffeine's half-life is 5–6 hours (slower on oral contraceptives, some genotypes). A 16:00 double espresso still has ~50mg circulating at 22:00 — measurably cutting deep sleep even when you fall asleep fine. The cutoff, not the dose, is what most people get wrong.

What to expect

Within 30–60 min: steadier focus block, less physical jitter than caffeine alone. Tolerance to the alertness effect builds in ~2 weeks of daily use; cycling or capping days preserves it.

How it is used

As the entry records it, from the studies it summarises. Not a recommendation for you — doses that suit a trial population may not suit you.

Standard stack: 100mg caffeine + 200mg theanine (1:2 ratio), morning or pre-deep-work.
Cutoff: Last caffeine ≥8–10h before bed. 14:00 for a 23:00 bedtime.

Goes with

Zone 2 trainingPre-session caffeine raises sustainable output at the same effortEvidence grade A

Questions people ask

Theanine alone?

Mild calm-focus signal, much weaker than the stack. Better used as caffeine's passenger.

Tolerance reset?

5–7 caffeine-free days restores most sensitivity; expect two rough mornings.

Entries that share this one's tags or conditions.

L-TheanineThe calm in green tea — pairs with caffeine to keep the focus and drop the jitter.Evidence grade B
L-Theanine for Acute stress / anxietyEvidence grade B — Non-sedating calmEvidence grade B
L-Theanine for Attention (with caffeine)Evidence grade B — Smoother focus, less jitterEvidence grade B
L-Theanine for Sleep qualityEvidence grade C — Relaxation, not sedationEvidence grade C

Sources

As this entry records them: title, journal and year. None carries a DOI or PubMed id, so none is linked as a verified paper. Each link searches PubMed for the title; check that what you find is what the entry describes.

1.L-theanine and caffeine on cognition and mood: systematic review — Nutr Neurosci, 2017. Search PubMed (opens in a new tab)
2.Caffeine effects on sleep taken 0, 3, or 6 hours before bed — J Clin Sleep Med, 2013. Search PubMed (opens in a new tab)
3.Caffeine and exercise performance: umbrella review — Br J Sports Med, 2020. Search PubMed (opens in a new tab)

Last revised Jun 12, 2026. A grade is this entry's reading of the evidence, not medical advice.