Drug & supplement interaction

Theanine + Doxepin

Doxepin brand names: Sinequan, Doxepin, Zonalon.

Minor Interaction
Medically reviewed by · Updated September 2026
The bottom line Minor

Doxepin falls into 2 drug categories that Theanine can interact with; the most serious is rated minor. Theoretically, theanine might have additive sedative effects when used in conjunction with CNS depressants.

Read the full interaction report
SeverityMinor
LikelihoodUnlikely
Interactions2
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Theanine and Doxepin

These two interact in 2 distinct ways. Each one is explained separately below.

Why Are There 2 Interactions?

Theanine interacts with whole categories of medication. Doxepin falls into 2 of those categories, so it can interact with Theanine in 2 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Minor).

Minor

CNS DEPRESSANTS

1 of 2

Why this applies to Doxepin

Doxepin falls under CNS DEPRESSANTS — the group Theanine interacts with.

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.
Severity Minor Likelihood Unlikely Evidence D

Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans..

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the simple version: doxepin already nudges you toward sleep, and theanine is thought to have a mild calming effect of its own, possibly by raising GABA, one of the brain's relaxing signals. Put them together and the worry is just a little extra drowsiness, like feeling groggier, foggy in the morning, or slower to wake up.

The good news is that this is a theoretical, minor concern based on how each works, not strong real-world data, and only some people in studies noticed any sleepiness from theanine. It's unlikely to cause trouble for most folks. Still, since both touch your alertness, mention it to your pharmacist or doctor before pairing them, and don't drive until you know how the combo affects you.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. 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.
  2. 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
Minor

SEROTONERGIC DRUGS

2 of 2

Doxepin also falls under 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.
Severity Minor Likelihood Unlikely Evidence C

Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans..

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the gist with doxepin and theanine. Doxepin is a tricyclic antidepressant that, among other things, nudges serotonin in the brain. Theanine may also touch serotonin, but the research is genuinely mixed: some studies say it raises serotonin, others say it lowers it. Because of that, the two have been flagged as a theoretical pairing.

In real life, this is rated minor and unlikely, and there are no actual reports of theanine causing serotonin-related problems. So I wouldn't lose sleep over it. Just be aware of how you feel, since doxepin already tends to cause drowsiness, dry mouth, and grogginess, and theanine is taken to relax you. If you notice extra sleepiness or feel off, check in with your pharmacist or doctor before changing anything.

Contact Dr. Brian directly if you have additional questions on this interaction

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Theanine Also Interacts With Other Medications

Theanine has 172 moderate, 392 minor known drug interactions in our database — the Doxepin one above is among them. If you take anything else, check it against the full list below.

Moderate 172 Minor 392 No known interaction 2,266 (incl. Doxepin)
Taking anything else?

Check Another of Your Medications Against Theanine

Covers the 2,830 medications we’ve checked against Theanine. Pick one to open its full report.

From our Q&A

Questions About Theanine or Doxepin

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Theanine or Doxepin, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Doxepin

This page covers Theanine only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Doxepin page lists 186 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: 1,4-butanediol (major), Activated Charcoal (major), American Hellebore (major), Arsenic (major) and Beer (major).

By severity: 15 major · 145 moderate · 26 minor.

From our pharmacist’s overview on the Doxepin page

“Doxepin is a sedating tricyclic prescribed for depression, anxiety, and often sleep itself, and the people taking it tend to shop the same shelf where the trouble sits. Of the 186 supplements on file, 78 deepen its drowsiness, with alcohol (beer and wine carry major, well-documented ratings) and kava the clearest examples, and I would…”

Reviewed by 2 · Jul 18, 2026

Open the Doxepin interaction page

One more smart check

Taking Theanine as Part of a Dietary Supplement Product? Check It for Interactions

We hold 3,298 real supplement products containing Theanine, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Theanine. Your product may carry other ingredients that interact with Doxepin too, on top of Theanine — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Theanine and Doxepin Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Theanine
Top 5%

#42 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Doxepin
Top half

#1,181 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Supplement

About Theanine

What is Theanine?

Theanine
  • Anxiety and stress
  • Relaxation and calm
  • Sleep support
  • Focus and cognitive function

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 help with relaxation and stress, but evidence for most uses is still limited. It appears generally well tolerated for short-term use, but check with your pharmacist or doctor before starting it.

Read the full Theanine monograph & all interactions
Medication

About Doxepin (Insomnia)

What Is Doxepin (Insomnia) Used For?

Brand names: Sinequan, Doxepin, Zonalon

This product is marketed to temporarily relieve occasional trouble sleeping when it's brought on by anxiety, restlessness, stress, or sensitivity to caffeine.

It is a homeopathic remedy — meaning its claims are based on traditional homeopathic practice, not accepted medical evidence, and it has not been evaluated by the FDA for effectiveness.

See full Doxepin (Insomnia) drug information
Keep checking

Other Drugs & Theanine

Browse every other medication we’ve checked against Theanine — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
172Moderate
392Minor
2,265No known interaction
172 Moderate 392 Minor 2,265 No interaction
Moderate

172 interactions

Showing 60 of 172 moderate interactions — see all 172 on the Theanine page.

Minor

392 interactions

Showing 60 of 392 minor interactions — see all 392 on the Theanine page.

No interaction 2,265 drugs checked — show the list

We also checked Theanine against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,265 medications checked with no known interaction — see the full Theanine list.

See the full Theanine interactions page
See every supplement checked against Doxepin, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

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

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
Theanine monograph › Uses, safety, and every drug interaction in one place Doxepin supplement interactions › Every supplement checked against Doxepin, ranked by severity Doxepin (Insomnia) drug information › The full plain-English guide to this medication Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Theanine and Doxepin Together: Common Questions

Can you take Theanine with Doxepin?
There is only a minor interaction, which is usually not serious. Read the full details on this page and confirm with your pharmacist before combining them.
Why are there 2 interactions listed for Theanine and Doxepin?
Doxepin belongs to more than one drug category, and Theanine interacts with each of those categories a little differently. We list every one so nothing is missed — your overall risk is driven by the most serious of them.
How serious is the Theanine and Doxepin interaction?
We rate it Minor. This interaction is generally not clinically significant, but it remains worth noting and discussing with your pharmacist.

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

Still Have a Question About Doxepin and Theanine?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.