Supplement Spotlight #8: L-Theanine
The versatile amino acid for relaxation & focus
To all my Substack friends - we’re back with another one.
Most users I know fall into one of two broad categories with L-theanine:
Poor reaction → troubling sleeping & minimal to no effect on stress levels
“Holy sh*t - this cured my anxiety & help me cut back on nicotine” → pair it with magnesium for sleep & caffeine for jitter-free energy
Rarely in between.
The only way of knowing how you’ll react to one of the most versatile compounds in existence? Conduct your own research & become sensitive to your individualized biofeedback.
What we’ll cover:
What is L-theanine?
How it Works
Benefits (as seen through the latest research)
Protocol
Reputable Brands
What is L-theanine?
L-theanine (N-ethyl-L-glutamine) is a non-protein amino acid found naturally in tea leaves. It has a chemical structure much like glutamate but exhibits a much different profile of physiological effects. More on that later.
One of the elite pharmacokinetic properties of L-theanine: its ability to be well absorbed from the intestine & cross the blood-brain barrier. This allows L-theanine to reach its site of action in the central nervous system and exert its biochemical effects directly on the neurotransmitter systems in our brain. The quick absorption & brain penetration explain the onset of effects within approximately 30-45 minutes after ingestion.
Mechanisms of Action
Neurotransmitter Regulation
L-theanine's interaction with neurotransmitter systems is critical to its anxiolytic & cognitive benefits. It impacts two primary neurotransmitter systems:
Glutamatergic → L-theanine acts on glutamate receptors as a competitive inhibitor for AMPA receptors & as a partial agonist at the glycine binding site on NMDA receptors.
L-theanine’s structural similarity to glutamate allows for the reduction of excitotoxicity & prevents neuronal overactivation via excess glutamate signaling.
GABAergic → L-theanine also enhances GABAergic activity by increasing GABA release indirectly through its interaction with glutamatergic neurons as suggested by evidence showing increased GABA receptor expression. Note here that the interaction is not a direct promotion of GABA release, but a function of the suppressed glutamate signaling.
The combination of these neurological impacts is what makes L-theanine so unique in that it induces the anxiolytic effects of relaxation & mood stability without making us drowsy.
Brain Wave Modulation
One mechanism we've only recently started to unravel is its ability to modulate alpha wave activity in the brain - frequencies between 8-12 Hz.
In other forms of research conducted over the past few decades, we've now associated these frequencies with a state of relaxed alertness, selective attention, & creative thinking. This modulation of brain electrical activity helps explain L-theanine's paradoxical ability to promote a relaxed aura without wanting to zonk out.
Health Benefits
Cognitive Function
This double-blind, placebo-controlled crossover study released in April 2025 examined the effects of L-theanine on selective attention in 24 sleep-deprived young adults using a traffic-related visual reaction task. A 200 mg dose of L-theanine significantly reduced false alarms & improved target-distractor discriminability compared to placebo.
A randomized controlled trial again investigated the effects of l-theanine and caffeine on attention discrimination using a randomized 4-way crossover design with 9 healthy adult men. Subjects received one of the following:
200 mg L-theanine
160 mg caffeine
200 mg L-theanine & 160 mg caffeine
A placebo
They then performed a visual color stimulus discrimination task during fMRI scans. L-theanine & the L-theanine + caffeine combination significantly improved response times to target stimuli. L-theanine also reduced neural activity tied to distractors & mind wandering.
In a placebo-controlled, five-way crossover trial with 20 healthy male volunteers, the acute effects of 200 mg L-theanine, 160 mg caffeine, their combination, black tea (one cup), & placebo (distilled water) on attention were investigated. L-theanine, caffeine, & their combination significantly improved recognition visual reaction time and increased P300 amplitudes compared to placebo, while black tea and placebo showed no significant effects.
Physical Performance & Cognitive Focus
A 2023 double-blind, placebo-controlled crossover study explored the effects of caffeine (CAF) and L-theanine (THE), alone or combined, on shooting accuracy and cognitive performance in 22 elite curling athletes. The dosages administered across the groups:
Caffeine Only: 6 mg/kg body weight (single dose)
L-theanine Only: 6 mg/kg body weight (single dose)
Caffeine & L-theanine: 6 mg/kg CAF + 6 mg/kg THE
Placebo: 400 mg maltodextrin
The caffeine & L-theanine group significantly improved shooting performance across various shot styles and improved reaction times relative to placebo.
The combined caffeine & theanine group also demonstrated enhanced accuracy in cognitive tasks compared to placebo or single supplement use.
Reaction Times
This double-blind, placebo-controlled crossover study examined the effects of L-theanine (100 mg, 200 mg, and 400 mg) versus a placebo on attention-related cognitive tasks in 32 healthy young adults. L-theanine significantly improved simple reaction times in a visuomotor task (RTI) at 100 mg and 200 mg doses compared to placebo.
In another randomized, double-blind, placebo-controlled crossover trial, 20 male collegiate athletes were given a supplement containing caffeine, theanine, & tyrosine or a placebo in two separate sessions. The theanine-based supplement improved movement accuracy from 0.4% to 7.5% (vs. -1.4% to 1.4% with placebo) in both static & dynamic performance tests.
Neurodevelopment Disorders
ADHD
In a small crossover trial with five boys (ages 8–15) with ADHD, single doses of the following were tested, each separated by a washout period:
L-theanine (2.5 mg/kg)
Caffeine (2.0 mg/kg)
L-theanine (2.5 mg/kg) + Caffeine (2.0 mg/kg)
Placebo
L-theanine alone improved overall cognition but tended to worsen inhibitory control, while caffeine alone worsened inhibitory control.
The caffeine + L-theanine combination improved both overall cognition & sustained attention with a trend toward better inhibitory control compared to placebo.
In another double-blind, placebo-controlled, 4-way crossover trial with 27 healthy young adults, single doses of L-theanine (100, 200, & 400 mg) or placebo were tested with cognitive event-related potentials measured before and 50 minutes after dosing. Only the 400 mg dose significantly improved attentional processing (reduced the latency of the parietal P3b ERP component). Each 100 mg increase reducing latency by 4 ms.
A 10-subject placebo-controlled, randomized double-blind crossover study tested the efficacy of L-theanine along. Each subject received a single 400 mg oral dose of L-theanine or placebo on two separate visits at least 72 hours apart. 30 minutes after taking L-theanine, subjects had significantly greater increases in intracortical facilitation (ICF) & long-interval intracortical inhibition (LICI) compared to placebo.
ICF → glutamate signaling = greater activation of neurons to communicate & coordinate
LICI → GABA signaling = regulated overexcitation via glutamate signaling
In a randomized, double-blind, placebo-controlled trial, 98 boys aged 8–12 with ADHD took either 400 mg of L-theanine daily (two 100 mg chewable tablets twice a day) or placebo for six weeks. The L-theanine group showed significantly improved sleep efficiency and a higher percentage of time spent asleep, as measured by actigraphy, but there was no change in sleep latency or other sleep parameters.
Schizophrenia
In an 8-week, double-blind, randomized, placebo-controlled trial, 60 patients with schizophrenia received either 400 mg/day of L-theanine or placebo as an adjunct therapy to their antipsychotic treatment. The addition of L-theanine significantly reduced anxiety-related symptoms (via PANSS model) with modest to moderate effect sizes relative to the placebo group:
Reduced positive factor symptoms (p = 0.004)
Reduced activation factors (p = 0.006)
Reduced mood factors (p = 0.019)
Psychological Health
Stress Management
In a single-blind study, 20 fifth-year pharmacy students took either 200 mg L-theanine or placebo tablets twice daily (total 400 mg/day) for one week before and ten days during their pharmacy practice. The theanine group had significantly lower morning salivary α-amylase (a stress marker) and reported less subjective stress compared to placebo.
In another similar randomized, placebo-controlled, double-blind, crossover trial, 30 healthy adults took either L-theanine (200 mg/day) or placebo for 4 weeks. Compared to placebo, L-theanine significantly improved stress-related symptoms & cognitive function:
Reduced self-rated depressive symptoms by 5.7% (p = 0.02)
Reduced self-assessed anxiety levels by 6.6% (p = 0.006)
Improved verbal fluency by 9.1% (p = 0.001)
Improved executive function by 6.3% (p = 0.03)
Immune Function
Exercise Recovery
In a double-blind, placebo-controlled trial with 20 elite Polish rowers, participants received either 150 mg of L-theanine daily or placebo for 6 weeks. L-theanine supplementation led to significant post-exercise inflammatory balance improvements:
Decreases in the anti-inflammatory cytokine IL-10
Increases in IL-2/IL-10 ratio
IL-2/IL-10 measurements before & after supplementation periods Increases in IFN-γ/IL-10 ratios
IFN-γ/IL-10 measurements before & after supplementation periods
Metabolic Health
In a 14-subject study measuring L-theanine’s effects on blood pressure, each person completed three separate trials where they took either 200 mg L-theanine + placebo, 100 mg caffeine + placebo, or placebo only. After performing mental tasks, L-theanine significantly reduced blood pressure increases & lowered tension-anxiety scores in individuals who had a high stress response, while caffeine alone had only a small effect on blood pressure.
Protocols
One of the reasons L-theanine has evolved into one of my favorite compounds is its versatility. Pairs well with caffeine for cognitive focus & physical performance. Synergistic for sleep when paired with Mg forms like glycinate & threonate.
The following protocols were developed based on a combination of user feedback, personal research, & clinical *human* trials.
Sleep
L-Theanine Dosage: 400 mg
Adjunct Compounds:
Magnesium Glycinate → 600 mg
Glycine → 4 g
Timing: 30 min before bed
Cognitive Focus
L-Theanine Dosage: 200 mg
Adjunct Compounds:
Caffeine → 100 mg
Lion’s Mane → 500 mg (8:1 extract)
Rhodiola Rosea → 300 mg
Ginkgo Biloba (50:1 extract) → 400 mg
Timing: 20 min before focus session
Pre-Workout
L-Theanine Dosage: 600 mg
Adjunct Compounds:
Citrulline → 6 g
Creatine Monohydrate → 10 g
Caffeine → 300 mg
Sea Salt → 500 mg
Timing: 20 min before warm-up period
*Note: Subjects are assumed to be 180 lb males with a dialed-in health foundation (i.e. sleep + movement + light environment + resistance training + nutrition).
Reputable Sources
Can't we naturally obtain L-theanine from tea?
Yes - but not nearly enough to have a noticeable effect.
Green tea: 6 - 20 mg/cup
Black tea: 8 - 20 mg/cup
White tea: 10 - 20 mg/cup
Oolong tea: 2 - 24 mg/cup
*Note: Typical tea leaves’ weight ~1.5 - 2 g/cup*
That’s why we turn to L-theanine’s supplement form for the benefits of the compound. Based on personal use, Consumer Lab reports, & user feedback, some brands I trust with high potency & purity formulas and possess trusted reputations:
**Doctor’s Best L-Theanine** (Phys Value Pick)
Cost/200 mg: $0.22
*Thorne Theanine* (Phys Overall Quality Pick)
Cost/200 mg: $1.00
Pure Encapsulations L-Theanine
Cost/200 mg: $1.02
Jarrow Formulas Extra Strength Theanine
Cost/200 mg: $0.42
We’re more bullish than ever on the future here. As always, stay healthy & we’ll see you next week.
Your friend,
BTP
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