Drug & supplement interaction

Theanine + Epoprostenol

Epoprostenol brand name: Flolan.

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

Theanine has a moderate interaction with Epoprostenol. Theanine might lower blood pressure, potentiating the effects of antihypertensive drugs.

Read the full interaction report
SeverityModerate
LikelihoodPossible
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Theanine and Epoprostenol

Here is the interaction we found between these two, with the evidence behind it.

Moderate

ANTIHYPERTENSIVE DRUGS

Why this applies to Epoprostenol

Epoprostenol falls under ANTIHYPERTENSIVE DRUGS — the group Theanine interacts with.

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.
Severity Moderate Likelihood Possible Evidence D

Interaction 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.

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

Here's the thing to keep in mind: epoprostenol (Flolan) already lowers blood pressure and widens blood vessels as part of how it treats pulmonary hypertension. Theanine, the calming amino acid from tea, may gently nudge blood pressure down too. Put them together and, in theory, those effects could stack up.

I want to be honest about the evidence here, though. This concern comes only from animal studies, so it's more of a theoretical caution than something proven in people. Still, if your blood pressure drifted too low, you might feel dizzy, lightheaded, flushed, or get a headache. If you take epoprostenol and want to try theanine, please run it by your pharmacist or doctor first so they can keep an eye on things.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Yokogoshi H, Kobayashi M. Hypotensive effect of gamma-glutamylethylamide in spontaneously hypertensive rats. Life Sci 1998;62:1065-8.
  2. 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

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 171 moderate, 393 minor known drug interactions in our database — the Epoprostenol one above is one of them. If you take anything else, check it against the full list below.

Moderate 171 Minor 393 No known interaction 2,266 (incl. Epoprostenol)
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 Epoprostenol

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 Epoprostenol, 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 Epoprostenol

This page covers Theanine only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Epoprostenol page lists 136 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), American Hellebore (major), American Mistletoe (major), Tyramine (major) and Adrafinil (moderate).

By severity: 4 major · 111 moderate · 21 minor.

From our pharmacist’s overview on the Epoprostenol page

“American hellebore tops my concerns for anyone on epoprostenol (Flolan), the continuous infusion that opens blood vessels in the lungs to treat pulmonary arterial hypertension. The herb lowers blood pressure even in small doses, and stacked on a medicine that already relaxes those vessels, the drop can be dangerous.”

Reviewed by 2 · Jul 18, 2026

Open the Epoprostenol 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 Epoprostenol 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 Epoprostenol 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 Epoprostenol
Top half

#716 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 Epoprostenol

What Is Epoprostenol Used For?

Brand name: Flolan

Epoprostenol (available as the brands Epoprostenol, Flolan, and Veletri) is used to treat pulmonary arterial hypertension (PAH) — WHO Group 1, a type of high blood pressure in the arteries of the lungs. The goal is to improve how much physical activity patients can handle.

The clinical studies that established its effectiveness included mainly patients with moderate-to-severe symptoms (NYHA Functional Class III–IV) whose PAH was idiopathic (no known cause), heritable (genetic), or related to connective tissue diseases such as scleroderma.

See full Epoprostenol 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
171Moderate
393Minor
2,265No known interaction
171 Moderate 393 Minor 2,265 No interaction
Moderate

171 interactions

Showing 60 of 171 moderate interactions — see all 171 on the Theanine page.

Minor

393 interactions

Showing 60 of 393 minor interactions — see all 393 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 Epoprostenol, 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 Epoprostenol supplement interactions › Every supplement checked against Epoprostenol, ranked by severity Epoprostenol 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 Epoprostenol Together: Common Questions

Can you take Theanine with Epoprostenol?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Theanine and Epoprostenol interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

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

Still Have a Question About Epoprostenol 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.