Interactions on record — worth a quick check against your medications. Check your meds →
Dietary supplement

L-Theanine 150 mg Ingredients & Drug Interactions

by Doctor's Best

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

L-Theanine 150 mg is a dietary supplement by Doctor's Best 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 150 mg by Doctor's Best

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.

Doctor's Best L-Theanine contains one active ingredient: L-theanine, an amino acid derived from tea leaves. The capsule also includes microcrystalline cellulose, hypromellose, and silicon dioxide as inactive ingredients (the binders and capsule material that hold it together).

Does it work?

Not established
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
Not established

The graded evidence we hold for these ingredients covers different conditions than the ones this product is marketed for, so there's no established rating for its stated use — see Theanine's own graded uses on its monograph.

Why this rating?
  • The label markets this product for: promote relaxation and reduce stress without drowsiness.
  • We looked for evidence on: Generalized anxiety disorder (GAD), Stress, anxiety, tension relief, mood support.
  • The closest evidence on file: Theanine is rated "Insufficient Reliable Evidence To Rate" for Generalized anxiety disorder (GAD) (Natural Medicines).
  • Also on file: Theanine is rated "Insufficient Reliable Evidence To Rate" for Stress.

L-theanine is possibly effective for cognitive function — that's the only use where the evidence leans toward benefit. For age-related cognitive decline, Alzheimer's disease, generalized anxiety disorder, obsessive-compulsive disorder, and cancer, the evidence we hold is insufficient to say whether it works or not.

If you're considering it for one of those other uses, talk it over with your doctor about what the current research shows.

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 long-term safety hasn't been well studied. Some people report headaches, drowsiness, longer sleep, or more vivid dreams after taking it.

One pediatric case of facial tics was reported within days of starting a much higher dose (400 mg daily), but the child had a history of tics and they stopped when the supplement was discontinued — so the link wasn't clear. There isn't enough safety data for use during pregnancy or while breastfeeding.

Talk with your doctor or pharmacist before taking this if you're pregnant, planning to become pregnant, or nursing.

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 L-Theanine, double-check if you take any blood pressure medications (antihypertensives) — theanine may make them work too well and drop your pressure too low. Also check if you take sleep aids, anxiety medications, or any central nervous system depressants, since additive sedation is possible.

If you're on serotonin-boosting antidepressants or other serotonergic drugs, the evidence is mixed on how theanine affects serotonin, but no cases of serotonin syndrome have been reported — still worth confirming with your pharmacist.

Check your own medication Run your meds through the checker above

The bottom line

Scorecard at a glanceFully disclosed formula with no established evidence rating for its marketed use. Moderate medication interactions have been identified, and safety information is well characterized.

L-theanine may help with focus and mental clarity based on the evidence we have, but it's best known for potentially relaxing effects. If you take blood pressure medications or sleep aids, check with your doctor or pharmacist before starting it — the combination could lower your blood pressure or increase drowsiness more than expected.

For short-term use in otherwise healthy adults, it's generally well tolerated, though headaches and vivid dreams happen in some people.

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 Jun 16, 2022.

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 150 mg, straight from the product label.

Brand Doctor's Best
Barcode (UPC) 753950001978
Net contents 90 Veggie Cap(s)
Market status On market
Date entered into DSLD Jun 16, 2022
DSLD ID 269486
Product type Non-nutrient/non-botanical
Supplement form Capsule
Dietary claims / uses All Other, Structure/Function
Intended target group(s) Vegan, Vegetarian, Adult (18 - 50 Years), Women (not pregnant or lactating), Gluten 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 150 mg by Doctor's Best, 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 Veggie Capsule(s)
Maximum serving Sizes:
1 Veggie Capsule(s)
Servings per container
90
UPC/BARCODE
753950001978
IngredientAmount% DV
L-Theanine150 mg--

Other ingredients: Microcrystalline Cellulose, Hypromellose, 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.
Formula

Doctor's Best L-Theanine contains Suntheanine, the purest form of L-Theanine on the market produced via a patented process that mimics the natural process in green tea leaves. L-Theanine helps promote a healthy mood and a restful relaxed state while maintaining daytime alertness.

General Statements

Helps promote a relaxed state without drowsiness Helps ease stress and everyday nervous tension Helps promote a healthy mood and alertness Helps diminish normal symptoms of premenstrual syndrome (PMS)

FDA Disclaimer Statement

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

Brand IP Statement(s)

Science-Based Nutrition Doctor's Best

Suntheanine is a registered trademark of Taiyo International, Inc.

Formulation

Helps promote relaxation without drowsiness Helps reduce stress and tension

Vegan

Non-GMO Gluten free Soy free

FDA Statement of Identity

Dietary Supplement

Suggested/Recommended/Usage/Directions

Suggested Adult Use: Take 1 capsule daily without food, or as recommended by a nutritionally informed physician.

Precautions

Warning: Not recommended for individuals who are pregnant and nursing.

Storage

Store in a cool dry place.

See for yourself

L-Theanine 150 mg by Doctor's Best label

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

What’s inside

The Ingredients in L-Theanine 150 mg by Doctor's Best

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

Serving size1 Veggie Capsule(s) Dosage formCapsule Servings per container90 Amounts shown are per serving.

L-Theanine

Interacts with
565 drugs
150 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, Hypromellose, Silicon Dioxide. These complete the product’s ingredient list but are not active constituents.

Interaction report

L-Theanine 150 mg by Doctor's Best Drug Interactions

Want to check YOUR meds against L-Theanine 150 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 150 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 150 mg, from the product label.

Doctor's Best

See all Doctor's Best products
Name
Doctor's Best, Inc.
State
California
ZipCode
92612
Phone Number
(800) 777-2474
Web Address
drbvitamins.com
Pharmacist Counseling Corner

L-Theanine 150 mg by Doctor's Best: Common Questions

Does L-Theanine 150 mg by Doctor's Best interact with any medications?
Yes. Based on its ingredients, L-Theanine 150 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 150 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.
What does L-theanine actually do?
L-theanine is an amino acid found naturally in tea. It's possibly effective for cognitive function — things like focus and mental clarity — but evidence for other uses like anxiety or age-related memory loss isn't established enough to say it works. Many people report it has a calming effect without making them drowsy.
Can I take this while I'm on blood pressure medication?
Not without checking first. Theanine may lower blood pressure on its own, so combining it with blood pressure drugs could cause your pressure to drop too far. Talk with your doctor or pharmacist before starting it if you take any antihypertensives.
Will L-theanine make me sleepy?
Some people report drowsiness, increased sleep duration, or more vivid dreams, but it's not a guaranteed side effect. The most common complaint is headaches. If you take sleep aids or anxiety medications, the sedative effect could be stronger when combined.
Is it safe to take while pregnant or breastfeeding?
There isn't enough safety data to know either way. The facts advise avoiding it during pregnancy and while breastfeeding. Talk with your doctor or pharmacist about your specific situation before taking it.
How long can I safely take L-theanine?
It's generally well tolerated for short-term use in healthy adults, but long-term safety hasn't been well studied. If you're planning to use it regularly for weeks or months, check in with your doctor or pharmacist about what's right for you.

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

Not sure if L-Theanine 150 mg is safe with your meds?

Our pharmacists answer your medication & supplement questions — free.

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 150 mg label
Go deeper

The Full Monographs Behind L-Theanine 150 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 150 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

Keep exploring