L-Theanine

Unique amino acid that promotes relaxation without sedation, enhances focus, and supports stress management

Scientific nameN-ethyl-L-glutamine FormulaC7H14N2O3 Molecular weight174.2 g/mol CAS3081-61-6

90 absorption score

9 safety / 10

20 USD per month

5 documented interactions

Check it against something

Evidence level A

L-Theanine with:

94 out of 100

Works better together Compatible. Timing differs, so follow each supplement's own window.

Check it against your whole stack →

What it does

mechanism and evidence for each claim

Promotes calm relaxation without drowsiness

Reduces stress and anxiety while maintaining alertness

Increases alpha brain waves promoting relaxed alertness Evidence A-grade 30 minutes to 2 hours

Enhanced focus and cognitive performance

Improves attention, focus, and mental clarity

Modulates neurotransmitters and reduces cortical arousal Evidence B-grade 1-4 hours

Stress and anxiety reduction

Reduces stress hormones and anxiety symptoms

Reduces cortisol and promotes GABA activity Evidence A-grade 30 minutes to 2 hours

Improved sleep quality

Enhances sleep quality without causing sedation

Promotes relaxation and reduces racing thoughts Evidence B-grade 1-2 hours before bed

Synergistic effects with caffeine

Reduces caffeine jitters while maintaining alertness

Balances caffeine's stimulating effects with calm focus Evidence A-grade 30 minutes to 4 hours

Others take these for the same thing

Same goal, different mechanism — check any of them against this one

Melatonin Sleep support & circadian rhythm 0.5-3mg A 50% Ashwagandha Stress management & energy 300-600mg A 75% Magnesium Glycinate Superior absorption sleep & muscle support 200-600 mg A 90% Vitamin B12 (Cyanocobalamin) Energy & nerve support 250-1000 mcg A 70% Fish Oil (EPA/DHA) Heart & brain health 1-2g EPA/DHA A 85% Vitamin B8 (Inositol) Mental health & PCOS support 2-18g (condition dependent) B 95%

Every pair we checked

12 combinations scored by the engine

L-Theanine + Creatine Monohydrate No documented interaction either way No known interaction 70

L-Theanine + Vitamin D3 No documented interaction either way No known interaction 70

L-Theanine + Calcium Carbonate No documented interaction either way No known interaction 70

L-Theanine + Whey Protein No documented interaction either way No known interaction 70

L-Theanine + Lactase No documented interaction either way No known interaction 70

L-Theanine + Bovine Collagen No documented interaction either way No known interaction 70

L-Theanine + DHA No documented interaction either way No known interaction 70

L-Theanine + Turmeric No documented interaction either way No known interaction 70

L-Theanine + Fish Oil (EPA/DHA) No documented interaction either way No known interaction 70

L-Theanine + Magnesium Oxide Enhanced relaxation and stress relief Works better together 78

L-Theanine + GABA (Gamma-Aminobutyric Acid) Enhanced calming and anti-anxiety effects Works better together 86

L-Theanine + Caffeine Enhanced focus with reduced jitters and anxiety Works better together 94

Dosage

As needed or with caffeine

Daily100-400mg

Stress anxiety100-200mg as needed

Focus with caffeine100-200mg with 50-100mg caffeine

Sleep support100-200mg 1-2 hours before bed

Daily stress management200-400mg divided doses

When to expect it

First Effects30-60 minutes for relaxation and focus benefits

Peak Benefits1-4 hours for sustained calm focus

Deficiency DevelopmentReturn to baseline stress and anxiety levels

Toxicity OnsetExtremely rare, excellent safety profile

How to measure it

Not applicable

MarkerNot routinely measured - assess through stress/anxiety symptoms

OptimalReduced stress markers and improved mood indicators

Deficient belowNot applicable for supplement

FrequencyMonitor through symptom improvement

What people actually reported to the FDA

CAERS, 23 reports naming it as the suspect

Most reported effects

Fatigue 3

Cough 3

Diarrhoea 3

Nausea 3

Dyspnoea 2

Named as the suspect 23 reports of 44 that mention it at all

Serious outcome 88% hospitalisation, emergency room or worse

Other Serious or Important Medical Event18

Life Threatening4

Visited Emergency Room4

Reports are voluntary and unverified — they record what someone experienced while taking something, not what the compound caused. Counts skew towards products people take a lot of, and a serious outcome is more likely to be reported than a mild one, so these are not rates. How we filter them →

What actually reaches you

The label counts the carrier, your body does not

Absorption Very high 90 of 100 · best absorbed form of this compound

Delivered daily 225 mg

Cost per 100 mg delivered $0.30 comparative — uses the absorption score, not a measured percentage

Works better with

3 documented

Caffeine

Enhanced focus with reduced jitters and anxiety

L-theanine balances caffeine stimulation with calm alertness · level A

Magnesium

Enhanced relaxation and stress relief

Both promote relaxation through different neurotransmitter pathways · level B

Gaba

Enhanced calming and anti-anxiety effects

Both promote GABA activity reducing anxiety · level B

What not to take with L-Theanine

2 documented

Excessive Stimulants

Very high stimulant intake may overwhelm calming effects

Excessive stimulation may counteract relaxation benefits · minor significance

Alcohol

Alcohol may interact with relaxation effects

Both have calming effects but different mechanisms · minor significance

Medication interactions

Discuss these with a pharmacist before combining

blood-pressure-medications Minor

May enhance blood pressure lowering effects

What to do: Monitor blood pressure

sedative-medications Minor

May enhance sedative effects

What to do: Use caution with sedatives

stimulant-medications Beneficial

May reduce stimulant side effects

What to do: May improve tolerance

Available forms

bioavailability compared

L-Theanine (Suntheanine) 90

Generic L-Theanine 85

L-Theanine (Suntheanine): Fast acting, No drowsiness, Excellent safety, Synergizes with caffeine

Generic L-Theanine: Lower cost, Same basic effects, Good availability, Well-tolerated

Food sources

before you supplement

Green tea 20-50mg per cup · 80

Black tea 5-25mg per cup · 75

White tea 15-30mg per cup · 80

L-Theanine supplements 100-200mg per capsule · 90

Too little

deficiency signs

Increased stress and anxiety levels
Poor focus and concentration
Difficulty managing daily stress
Caffeine jitters and overstimulation
Racing thoughts and mental restlessness
Poor stress recovery
Difficulty achieving calm focus

Too much

toxicity signs

Extremely safe with minimal side effects:
Mild drowsiness in very sensitive individuals
Slight blood pressure reduction
Rare headaches with very high doses
Generally very well tolerated

Who benefits most

stress-anxiety-management

Excellent for reducing stress and anxiety without sedation

100-200mg as needed

focus-concentration-adhd

Improves focus and attention, especially when combined with caffeine

100-200mg with caffeine

sleep-quality-insomnia

Improves sleep quality by promoting relaxation

100-200mg 1-2 hours before bed

caffeine-users-jitters

Reduces caffeine side effects while maintaining alertness

100-200mg with coffee/caffeine

students-cognitive-performance

Enhances learning and cognitive performance under stress

100-200mg before studying

Where to buy it

compare forms first

Look for L-Theanine at 100-400mg per serving. The form that matters here is L-Theanine (Suntheanine).

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What else affects it

Beyond other supplements

Excessive stimulants

Very high stimulant intake may overwhelm calming effects

Excessive stimulation may counteract relaxation benefits

Alcohol

Alcohol may interact with relaxation effects

Both have calming effects but different mechanisms

How it works

Increases alpha brain wave activity promoting relaxed alertness
Enhances GABA neurotransmitter activity reducing anxiety
Modulates dopamine and serotonin for improved mood
Reduces cortisol stress hormone levels
Blocks glutamate receptors reducing neural excitation
Crosses blood-brain barrier easily for direct brain effects

Key findings

what the evidence supports

Excellent evidence for stress reduction and calm focus
Strong synergy with caffeine for enhanced cognitive performance
Outstanding safety profile with minimal side effects
Fast-acting with effects lasting 4-6 hours

Sources: NIH Examine.com · data reviewed 2026-08-02

Compiled by Denis, who maintains this database and holds no medical qualification — every figure here is sourced or derived, never asserted. How we calculate it →

Common questions

What are the benefits of L-Theanine?

Documented effects: Promotes calm relaxation without drowsiness; Enhanced focus and cognitive performance; Stress and anxiety reduction; Improved sleep quality. Reduces stress and anxiety while maintaining alertness

How much L-Theanine should you take per day?

The common daily range is 100-400mg. By goal — stress anxiety: 100-200mg as needed; focus with caffeine: 100-200mg with 50-100mg caffeine; sleep support: 100-200mg 1-2 hours before bed; daily stress management: 200-400mg divided doses.

When is the best time to take L-Theanine?

As needed or with caffeine. First effects are typically reported within 30-60 minutes for relaxation and focus benefits.

What are the side effects of L-Theanine?

At excessive doses: Extremely safe with minimal side effects:, Mild drowsiness in very sensitive individuals, Slight blood pressure reduction, Rare headaches with very high doses, Generally very well tolerated. Safety rating at normal doses is 9 out of 10.

What should you not take with L-Theanine?

Separate it from Excessive Stimulants, Alcohol by two to four hours. Very high stimulant intake may overwhelm calming effects

Does L-Theanine interact with medications?

Documented interactions with blood-pressure-medications, sedative-medications, stimulant-medications. Discuss these with a pharmacist before combining.

How do you know if you need L-Theanine?

The marker is Not routinely measured - assess through stress/anxiety symptoms, optimal range Reduced stress markers and improved mood indicators. Common deficiency signs: Increased stress and anxiety levels, Poor focus and concentration, Difficulty managing daily stress, Caffeine jitters and overstimulation.

Taken for

52 Brain & Focus

Caffeine · DHA · Fish Oil (EPA/DHA)

28 Sleep & Stress

Melatonin · Magnesium Glycinate · Ashwagandha