L-theanine

What it is

L-theanine is an amino acid found almost exclusively in tea. It crosses into the brain and increases alpha-band EEG activity — the electrical signature of relaxed alertness — without sedation. That profile explains both of its uses: paired with caffeine it supports attention while smoothing caffeine’s edge; taken alone it supports calm.

The attention evidence in the table below is specifically about the caffeine pairing — crossover trials found the combination improved attention-task accuracy and task-switching beyond either compound alone. On its own, theanine has a smaller trial base: one four-week study showed lower stress-scale scores. It is among the better-tolerated supplements in our catalog.

Evidence by goal

• BB — one solid RCT or consistent meta-analytic signal Focus

  Paired with caffeine, improved attention-task accuracy, task-switching, and self-rated alertness versus either compound alone in crossover trials; alone, it raises the alpha-band activity linked to relaxed alertness.

  Haskell CF, 2008 · Giesbrecht T, 2010 · Nobre AC, 2008

• B Stress

  Four weeks of 200 mg per day lowered stress-scale scores and improved sleep-quality subscores versus placebo in one 30-person trial.

  Hidese S, 2019

Forms compared

• Capsule. Typically 100–200 mg per capsule — matches the doses trials used. The convenient default.
• Powder. Mildly savory taste; easy to stir into coffee or tea, which is exactly where the pairing evidence points.

Dose and timing

100–200 mg with your morning caffeine for attention work, or 200 mg on its own in the evening for calm. Trials of the pairing used theanine at or above the caffeine dose. It acts within the hour; there is no loading period.

Evidence-backed range: 100–400 mg per day.

Cautions and interactions

• L-theanine may modestly lower blood pressure. If you take blood-pressure medication and your readings already trend low, note the pairing.
• Evidence in pregnancy is thin — skip it there.

From our interaction tables

• monitor Blood-pressure medication (class). L-theanine may lower blood pressure modestly. Rarely a problem — worth knowing if your readings already trend low on medication.

Who should skip this

• People who are pregnant or nursing, given the thin safety data.
• People whose blood pressure runs low on medication, unless their clinician is comfortable with the addition.

Questions we actually get

What ratio of theanine to caffeine should I use?

The trials used theanine at or above the caffeine dose — for example 250 mg theanine with 150 mg caffeine, or roughly 100 mg with 40 mg of caffeine. Matching or exceeding your caffeine dose is a reasonable rule.

Will it make me drowsy?

No — the measured effect is relaxed alertness, not sedation. That is why it pairs with caffeine instead of working against it.

Is drinking tea enough?

A cup of tea delivers meaningfully less theanine than the 100–200 mg the trials used, along with a modest caffeine dose. Tea is pleasant; the trial doses came from capsules.

Can I take it every day?

The four-week daily trial showed no tolerance pattern and good tolerability. There is no evidence-based reason to cycle it.

Sources

1. Haskell CF, Kennedy DO, Milne AL, et al., Biological Psychology, 2008 — crossover RCT of theanine, caffeine, and their combination
2. Giesbrecht T, Rycroft JA, Rowson MJ, De Bruin EA, Nutritional Neuroscience, 2010 — crossover RCT of theanine 97 mg + caffeine 40 mg
3. Nobre AC, Rao A, Owen GN, Asia Pacific Journal of Clinical Nutrition, 2008 — EEG study of L-theanine and resting alpha activity
4. Hidese S, Ogawa S, Ota M, et al., Nutrients, 2019 — RCT of 200 mg/day L-theanine for 4 weeks