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Dietary supplement

L-Theanine 100 mg Ingredients & Drug Interactions

by Seeking Health

L-Theanine 100 mg label
See full label image
Capsule Category: Non-nutrient/non-botanical
Most serious interaction: Moderate
Clinical methodology reviewed by · Updated Sep 23, 2026 · Label data from the NIH DSLD
What is this page for?

First and foremost: checking L-Theanine 100 mg against your medications. The heart of this page is the interaction checker and the full interaction report — how this product’s ingredients may interact with prescription and over-the-counter medicines you may be taking.

Around that, we add a pharmacist’s high-level view of the product as a whole — what’s inside, the evidence for its stated use, how transparent the label is, and what safety data exists — so you can see the full picture in one place. It’s educational information from our licensed clinical databases and the clinical staff at HelloPharmacist — not medical advice — and we don’t sell or endorse products. Our editorial policy

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.

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Check Your Meds Against L-Theanine 100 mg by Seeking Health

Ask about any prescription or over-the-counter medication and we check it for interactions with L-Theanine 100 mg by Seeking Health — and tell you which ingredient is responsible.

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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

Generated from HelloPharmacist’s pharmacist-curated databases and editorial rules · Last generated Aug 13, 2026

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 that's known for its calming properties without causing drowsiness.

The capsule also contains cellulose, vegetarian capsule material, L-leucine, and silicon dioxide as inactive ingredients.

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 cognitive function according to the data we hold. For other uses — including age-related cognitive decline, Alzheimer disease, generalized anxiety, obsessive-compulsive disorder, and cancer — the evidence isn't established well enough to rate.

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 when used short-term, though long-term safety hasn't been well studied. Common side effects reported include headaches, drowsiness, increased sleep duration, and more vivid dreams.

The safety data advises against use during pregnancy and breastfeeding because there isn't enough information to know if it's safe for your baby.

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.

Check with your doctor or pharmacist before using this product if you take blood pressure medication, since theanine might lower your pressure further. Also flag any central nervous system depressants (sedatives, sleep aids, certain pain relievers) or serotonergic drugs (many antidepressants), which have documented but lower-priority concerns.

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. It's most important to check with your doctor or pharmacist before starting it if you take blood pressure medication or any sedatives or antidepressants.

If you're pregnant, breastfeeding, or planning either, talk with your healthcare provider first — the safety data for those situations isn't solid enough yet.

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 Mar 23, 2018.

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) 828054154995
Net contents 60 Vegetarian Capsule(s)
Market status On market
Date entered into DSLD Mar 23, 2018
DSLD ID 174493
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:
2 Capsule(s)
Servings per container
60
UPC/BARCODE
828054154995
IngredientAmount% DV
L-Theanine100 mg--

Other ingredients: Cellulose, Vegetarian Capsule, L-Leucine, 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 to 2 capsules daily or as directed by your health care professional.

Precautions

Do not use if shrinkwrap is broken or missing.

Keep out of reach of children.

Storage

Store in a cool, dry place (59(0)F-85(0)F) away from direct light.

General Statements

This product was made in a GMP and ISO 9001:2008 registered facility.

Physician formulated

FDA Statement of Identity

Dietary Supplement

Brand IP Statement(s)

Suntheanine is a registered trademark of Taiyo International, Inc.

Formulation

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

Is this label outdated? Report a formula or label change and our pharmacy team will review it.

See for yourself

L-Theanine 100 mg by Seeking Health label

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

L-Theanine 100 mg label

Label images are published by the NIH Dietary Supplement Label Database for the version of this product on file. Always read your actual product label.

View the full label (PDF)
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: Cellulose, Vegetarian Capsule, L-Leucine, 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

L-Theanine 565

Individual Drug Interactions

The ingredients in L-Theanine 100 mg interact with 565 drugs. Click any drug to see the details.

1 of the 1 ingredient in L-Theanine 100 mg interact with drugs. Each result below shows which ingredient is responsible. L-Theanine

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
L-Theanine full monograph & interactions
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 this while I'm on blood pressure medication?
Not without checking first. L-theanine can lower blood pressure, so combining it with your blood pressure medication might drop your pressure too much. Talk with your doctor or pharmacist about whether it's okay for you.
What are the side effects?
Headaches are the main one reported. Some people also experience drowsiness, longer sleep, or more vivid dreams after taking L-theanine.
Is this safe during pregnancy?
There isn't enough safety data to know either way, so the guidance is to avoid it during pregnancy. Talk with your doctor for personalized advice.
Does L-theanine actually improve memory and focus?
L-theanine is possibly effective for cognitive function based on the evidence we hold, but for specific concerns like age-related decline or Alzheimer disease, we don't have enough reliable data to say.
How long can I safely take this?
Short-term use in healthy adults is generally well tolerated. Long-term safety hasn't been well studied, so if you're thinking of taking it long-term, check with your doctor or pharmacist.
Can I take this with my sleep medication?
Not without asking your doctor or pharmacist first. L-theanine might have additive drowsy effects with sleep aids and other central nervous system depressants, though whether this is a real concern in practice isn't entirely clear.

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

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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.

Herb & supplement monograph

Theanine

Interacts with 565 drugs

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 drowsiness. Early research suggests it may...

Read the full Theanine monograph →
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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