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Dietary supplement

L-Theanine 100 mg Ingredients & Drug Interactions

by Seeking Health

Capsule Category: Non-nutrient/non-botanical
Most serious interaction: Moderate
The interaction bottom line Most serious interaction: Moderate

L-Theanine 100 mg is a dietary supplement by Seeking Health with 1 active ingredient. Its ingredients are commonly taken for anxiety and stress, relaxation and calm, sleep support.Based on those ingredients, 565 medications have a known interaction with it, the most serious rated moderate. The ingredients most likely to interact are L-Theanine. Use the checker below to test your specific medication, or read the full HelloPharmacist Interaction Report.

HelloPharmacist Scorecard of L-Theanine 100 mg by Seeking Health

Our pharmacy team’s full take, with four database checks built into the cards below — a summary of what is known, not a grade of the product itself.

From our pharmacy team — supplement deep dive

What’s inside

Full disclosure
Ingredient Transparency · database check
Full

Every active ingredient lists its own amount on the label.

Why this rating?
  • The label discloses an exact amount for 1 of its 1 active ingredient.
  • No proprietary blends here — you can verify the dose of every single component.

This product contains one active ingredient: L-Theanine 100 mg per capsule. L-Theanine is an amino acid found naturally in tea leaves.

The capsule also contains several inactive ingredients (microcrystalline cellulose, vegetarian capsule, L-Leucine, cellulose, and silicon dioxide), which are fillers and binders that help form and stabilize the supplement.

Does it work?

Moderate evidence
Evidence for Intended Use · database check
By FDA rules, dietary supplements can’t claim to treat, cure, or prevent disease — so labels speak in careful marketing language. We discern each product’s intended use from its name, label claims, and label statements, then grade the clinical evidence for that use. How these ratings are computed

This product doesn't appear to be marketed for a specific use, so we graded Theanine's overall clinical evidence instead.

Moderate

Some clinical evidence supports Theanine for:

Why this rating?
  • We looked at the product name, claims, and label statements and couldn't find a stated purpose to grade.
  • Since the label doesn't commit to one use, we graded the ingredient's overall clinical evidence instead.
  • On file: Cognitive function — rated "Possibly Effective" (Natural Medicines).

L-Theanine is possibly effective for supporting cognitive function based on available evidence. For age-related cognitive decline, Alzheimer disease, generalized anxiety disorder, obsessive-compulsive disorder, and cancer, the evidence we hold is insufficient to rate it one way or another—meaning research hasn't yet established whether it works for those uses.

The evidence, ingredient by ingredient Theanine

How safe is it?

Well-documented data
Safety Information · database check
Well characterized

Adverse-effect, pregnancy, and general safety data are on file for most of these ingredients.

Why this rating?
  • We hold adverse-effect (side-effect) data for 1 of the 1 matched ingredient.
  • Pregnancy & breastfeeding safety ratings cover 1 of 1.
  • General safety write-ups exist for 1 of 1.
  • Remember: this measures how much safety information exists. Thin data is not the same as being safe.

L-Theanine is generally well tolerated in healthy adults for short-term use, but how safe it is over the long term isn't well studied. The most common side effects reported are headaches, drowsiness, increased sleep duration, and more vivid dreams.

There isn't enough safety data to recommend L-Theanine during pregnancy or while breastfeeding—talk with your doctor or pharmacist about whether it's right for you if you're pregnant, nursing, or planning either.

Side effects, ingredient by ingredient Theanine

Meds to double-check

Moderate interaction found
Known Interaction Concern · database check
Moderate identified

The most serious documented interaction for these ingredients is Moderate. Check your medications for a personalized result.

Why this rating?
  • 1 of the 1 matched ingredient can interact with medications — Theanine.
  • The most serious interaction on file is rated Moderate.
  • For scale: 565 individual medications appear in the full list. A big number alone doesn't make a product dangerous — what matters is whether YOUR medication is on it, so run yours through the interaction checker on this page.

Before you start, check with your doctor or pharmacist if you take any blood pressure medications—L-Theanine could strengthen their effect and lower your blood pressure too much. Also flag any sedatives, sleep aids, pain relievers with sedating effects, or antidepressants, since L-Theanine may add to their drowsiness or, theoretically, interact with how your brain handles serotonin.

Check your own medication Run your meds through the checker above

The bottom line

Scorecard at a glanceFully disclosed formula with some supporting evidence behind its ingredients' uses. Moderate medication interactions have been identified, and safety information is well characterized.

L-Theanine may help with focus and mental clarity, but it's most important to check it against your current medications—especially blood pressure drugs, sedatives, and antidepressants. If you're pregnant or breastfeeding, there's not enough data to say it's safe, so discuss it with your doctor or pharmacist first.

This supplement is best for short-term use in healthy adults.

Educational only — not medical advice; always confirm with your pharmacist. Our editorial policy · How we use AI

Assessment coverage: 1 of 1 active ingredient matched to our full ingredient reviews (monographs). Based on the product label dated Jan 25, 2020.

This Scorecard evaluates available label information, ingredient evidence, and known medication-safety considerations. It does not independently verify product identity, purity, potency, contamination, or manufacturing quality. How these ratings are computed

At a glance

General information

Key facts about L-Theanine 100 mg, straight from the product label.

Brand Seeking Health
Barcode (UPC) 810007520636
Net contents 60 Vegetarian Capsules
Market status On market
Date entered into DSLD Jan 25, 2020
DSLD ID 210854
Product type Non-nutrient/non-botanical
Supplement form Capsule
Dietary claims / uses All Other
Intended target group(s) Adult (18 - 50 Years), Gluten Free, Dairy Free
From the label
Everything in this section is reproduced from the manufacturer’s own product label — it’s the label speaking, not HelloPharmacist. We show it so you can see exactly what the maker states; we don’t verify or endorse those statements.

Supplement Facts

The label details for L-Theanine 100 mg by Seeking Health, sourced from the NIH Dietary Supplement Label Database.

Supplement Facts

Daily Value (DV) Target Group(s):
Adults and children 4 or more years of age
Minimum serving Sizes:
1 Capsule(s)
Maximum serving Sizes:
1 Capsule(s)
Servings per container
60
UPC/BARCODE
810007520636
IngredientAmount% DV
L-Theanine100 mg--

Other ingredients: Microcrystalline Cellulose, Vegetarian Capsule, L-Leucine, Cellulose, Silicon Dioxide

Tap any ingredient to jump to its full detail below.

Label statements
These statements are the manufacturer’s wording, reproduced from the product label — the label is saying it, not HelloPharmacist. We don’t verify or endorse them.
Suggested/Recommended/Usage/Directions

Suggested Use: 1 capsule, 1 to 2 times daily or as directed by your healthcare professional.

Brand IP Statement(s)

Suntheanine is a registered trademark of Taiyo International, Inc.

Precautions

Children and pregnant or lactating women should consult their healthcare professional prior to use.

Children and pregnant or lactating women should consult their healthcare professional prior to use.

Do not use if shrinkwrap is broken or missing.

Keep out of reach of children.

Storage

Storage: Store in a cool, dry place below 85 degrees F away from direct light. Do not freeze.

Formulation

Does Not Contain: milk/casein, eggs, fish, shellfish, tree nuts, peanuts, wheat, gluten, yeast, and soybeans. Contains no artificial colors, flavors, or preservatives.

General Statements

L-Theanine meets or exceeds cGMP Quality Standards. Targeted Support

Find Other Effective Health Products At: www.SeekingHealth.com

FDA Statement of Identity

Dietary Supplement

See for yourself

L-Theanine 100 mg by Seeking Health label

The label scan from the NIH Dietary Supplement Label Database. Tap to enlarge.

What’s inside

The Ingredients in L-Theanine 100 mg by Seeking Health

This is the 1 active ingredient this product is made of. Select it to open its full monograph.

Serving size1 Capsule(s) Dosage formCapsule Servings per container60 Amounts shown are per serving.

L-Theanine

Interacts with
565 drugs
100 mg per serving

Theanine (usually L-theanine) is an amino acid found naturally in tea leaves that many people take to feel calmer and less stressed without strong dro...

L-Theanine monograph & interactions

Other (inactive) ingredients: Microcrystalline Cellulose, Vegetarian Capsule, L-Leucine, Cellulose, Silicon Dioxide. These complete the product’s ingredient list but are not active constituents.

Interaction report

L-Theanine 100 mg by Seeking Health Drug Interactions

Want to check YOUR meds against L-Theanine 100 mg?

Ask about interactions with your drugs in plain English — “Can I take it with lisinopril?” — and we find you the answer in seconds, ingredient by ingredient.

Go to the checker
565Drugs
172 Moderate 393 Minor

Ingredients driving the most interactions

Each ingredient & the kinds of drugs it affects

For each ingredient in L-Theanine 100 mg with known interactions, here are the types of medications it can affect. Open any type for the detail — or search your exact drug in the checker above.

L-Theanine3 drug types · 565 drugs

Antihypertensive Drugs

Theanine might lower blood pressure, potentiating the effects of antihypertensive drugs.
Animal research shows that theanine can lower blood pressure in spontaneously hypertensive animals. Theoretically, concomitant use of theanine and antihypertensive drugs might potentiate the antihypertensive activity.

Likelihood Possible Evidence D
Cns Depressants

Theoretically, theanine might have additive sedative effects when used in conjunction with CNS depressants. However, it is unclear if this concern is clinically relevant.
Theoretically, theanine may compete with glutamate and/or increase plasma gamma-aminobutyric acid (GABA) levels, which could cause CNS depression. In one clinical study, some subjects taking oral theanine reported drowsiness.

Likelihood Unlikely Evidence D
Serotonergic Drugs

Clinical studies regarding the effects of L-theanine on serotonin levels are conflicting. Some studies suggest it can increase serotonin levels in the brain while others report that it may decrease them. Nevertheless, there have been no reports of l-theanine being a causative agent in serotonergic-related side effects or serotonin syndrome.

Likelihood Unlikely Evidence C
The maker

Brand information

Manufacturer and brand details for L-Theanine 100 mg, from the product label.

Seeking Health

See all Seeking Health products
Name
Seeking Health
Street Address
3140 Mercer Ave
City
Bellingham
State
WA
ZipCode
98225
Phone Number
(800) 547-9812
Web Address
www.seekinghealth.com
Pharmacist Counseling Corner

L-Theanine 100 mg by Seeking Health: Common Questions

Does L-Theanine 100 mg by Seeking Health interact with any medications?
Yes. Based on its ingredients, L-Theanine 100 mg has a known interaction with 565 medications. Use the checker to see how it interacts with a specific drug.
How can one product interact with so many drugs?
L-Theanine 100 mg contains a single active ingredient, and that one ingredient can interact with many different medications on its own. We check it against each medication and show the mechanism responsible.
Where does this information come from?
The product label data comes from the NIH Dietary Supplement Label Database (DSLD); the interaction data is built on the Natural Medicines database and reviewed by HelloPharmacist pharmacists.
Can I take L-Theanine if I'm pregnant or breastfeeding?
There isn't enough safety data for L-Theanine during pregnancy or breastfeeding. Talk with your doctor or pharmacist before taking it if you're pregnant, nursing, or planning either—they can give you advice tailored to your situation.
What are the side effects of L-Theanine?
The most common side effects are headaches, drowsiness, increased sleep time, and more vivid dreams. It's generally well tolerated for short-term use, but long-term safety hasn't been well studied.
Does L-Theanine really work for anxiety or focus?
L-Theanine is possibly effective for cognitive function based on available evidence. For anxiety disorders, the evidence we have is not strong enough to say whether it works or not—more research is needed.
What is L-Theanine and where does it come from?
L-Theanine is an amino acid that occurs naturally in tea leaves. It's the ingredient in tea that's thought to promote calm focus without the jitters you might get from caffeine alone.
How long can I safely take L-Theanine?
L-Theanine is well tolerated in healthy adults for short-term use, but how safe it is over longer periods isn't well established. If you're thinking about taking it long-term, ask your doctor or pharmacist.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Not sure if L-Theanine 100 mg is safe with your meds?

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Ask a pharmacist

Label information is sourced from the NIH Dietary Supplement Label Database and reflects the product version on file; always read your actual product label. This page is for education only and is not a substitute for professional medical advice. Confirm with your pharmacist or doctor before combining supplements and medications.

L-Theanine 100 mg label
Go deeper

The Full Monographs Behind L-Theanine 100 mg’s Ingredients

Every ingredient we hold a full HelloPharmacist monograph for — uses, evidence, safety, and the complete interaction list.

Sources

Sources & How We Checked

L-Theanine 100 mg's label data comes from the NIH Dietary Supplement Label Database; the ingredient interaction data is from the Natural Medicines database, reviewed by our pharmacists.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

The 6 references behind this product’s interaction data

Every citation that drives the interaction findings for this product’s ingredients, from the evidence-graded Natural Medicines (TRC Healthcare) database. Open an ingredient to browse its citations — links open the study on PubMed or the publisher’s site.

Theanine 6 references
  1. Yokogoshi H, Kobayashi M. Hypotensive effect of gamma-glutamylethylamide in spontaneously hypertensive rats. Life Sci 1998;62:1065-8.
  2. Haskell, C. F., Kennedy, D. O., Milne, A. L., Wesnes, K. A., and Scholey, A. B. The effects of L-theanine, caffeine and their combination on cognition and mood. Biol.Psychol. 2008;77(2):113-122. PubMed
  3. Yokogoshi, H., Kato, Y., Sagesaka, Y. M., Takihara-Matsuura, T., Kakuda, T., and Takeuchi, N. Reduction effect of theanine on blood pressure and brain 5-hydroxyindoles in spontaneously hypertensive rats. Biosci.Biotechnol.Biochem. 1995;59(4):615-618. PubMed
  4. Lyon MR, Kapoor MP, Juneja LR. The effects of L-theanine (Suntheanine®) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trial. Altern Med Rev. 2011;16(4):348-
  5. Hidese S, Ota M, Wakabayashi C, et al. Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label study. Acta Neuropsychiatr 2017;29(2):72-9.
  6. Tsuchiya T, Honda H, Oikawa M, et al. Oral administration of the amino acids cystine and theanine attenuates the adverse events of S-1 adjuvant chemotherapy in gastrointestinal cancer patients. Int J Clin Oncol 2016;21(6):1085-90. PubMed

See these in context on the Theanine monograph →

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

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