Drug & supplement interaction

Guarana + Mephenytoin

Mephenytoin brand name: Mesantoin.

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

Guarana has a moderate interaction with Mephenytoin. Theoretically, guarana might reduce the effects of phenytoin and increase the risk for convulsions.

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

Guarana and Mephenytoin

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

Moderate

PHENYTOIN (Dilantin)

Theoretically, guarana might reduce the effects of phenytoin and increase the risk for convulsions.
Guarana contains caffeine. Animal research shows that caffeine can decrease the anticonvulsant activity of phenytoin. The effect does not seem to be related to the seizure threshold-lowering effects of caffeine. However, the exact mechanism of this interaction is unclear.
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 gist: mephenytoin (Mesantoin) is an older anti-seizure medicine, closely related to phenytoin. Guarana is loaded with caffeine, and animal studies hint that caffeine may chip away at how well this type of seizure drug works. The worry isn't that the drug builds up, it's that its protective, seizure-blocking effect could be weakened, which in theory could raise the chance of a breakthrough seizure.

I want to be honest about the evidence though. This is based on lab and animal research, not solid human studies, so it's more of a theoretical caution than a sure thing. Still, with a seizure medicine, even small shifts matter. A single cup of coffee is one thing, but concentrated guarana energy products are where I'd be more careful. Please check with your pharmacist or doctor before adding it.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Jankiewicz, K., Chroscinska-Krawczyk, M., Blaszczyk, B., and Czuczwar, S. J. [Caffeine and antiepileptic drugs: experimental and clinical data]. Przegl.Lek. 2007;64(11):965-967.
  2. Chroscinska-Krawczyk, M., Jargiello-Baszak, M., Walek, M., Tylus, B., and Czuczwar, S. J. Caffeine and the anticonvulsant potency of antiepileptic drugs: experimental and clinical data. Pharmacol.Rep. 2011;63(1):12-18. 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

Guarana Also Interacts With Other Medications

Guarana has 8 major, 461 moderate, 185 minor known drug interactions in our database — the Mephenytoin one above is one of them. If you take anything else, check it against the full list below.

Major 8 Moderate 461 Minor 185 No known interaction 2,176 (incl. Mephenytoin)
Taking anything else?

Check Another of Your Medications Against Guarana

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

Everything else you take

See Every Supplement That Interacts With Mephenytoin

This page covers Guarana only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Mephenytoin page lists 215 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), Beer (major), Gamma-hydroxybutyrate (ghb) (major) and Kava (major).

By severity: 9 major · 178 moderate · 28 minor.

From our pharmacist’s overview on the Mephenytoin page

“Anyone taking mephenytoin (Mesantoin) for seizures should read this page with genuine care rather than as background noise. The biggest cluster of interactions piles sedation on top of a drug that already slows the nervous system, and alcohol, whether beer or wine, sits at the serious end of that group.”

Reviewed by 2 · Jul 18, 2026

Open the Mephenytoin interaction page

One more smart check

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

We hold 1,430 real supplement products containing Guarana, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Guarana. Your product may carry other ingredients that interact with Mephenytoin too, on top of Guarana — 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 Guarana and Mephenytoin 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 Guarana
Top 10%

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

29 days ago today
Medication Mephenytoin
Steady interest

#2,240 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 Guarana

What is Guarana?

Guarana
  • Energy and alertness
  • Reducing fatigue
  • Weight loss support
  • Athletic performance
  • Mental focus

Guarana is an Amazonian seed that is naturally high in caffeine, which explains most of its stimulant and energy effects. While it may give a short-term boost in alertness and reduce fatigue, strong evidence for weight loss or major performance gains is limited, and it carries the same risks as too much caffeine. Talk to your pharmacist or doctor before using it, especially if you have heart problems, anxiety, or are pregnant.

Read the full Guarana monograph & all interactions
Keep checking

Other Drugs & Guarana

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

8Major
461Moderate
185Minor
2,175No known interaction
8 Major 461 Moderate 185 Minor 2,175 No interaction
Major

8 interactions

Moderate

461 interactions

Showing 60 of 461 moderate interactions — see all 461 on the Guarana page.

Minor

185 interactions

Showing 60 of 185 minor interactions — see all 185 on the Guarana page.

No interaction 2,175 drugs checked — show the list

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

Showing the 60 most looked-up of 2,175 medications checked with no known interaction — see the full Guarana list.

See the full Guarana interactions page
See every supplement checked against Mephenytoin, 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
Guarana monograph › Uses, safety, and every drug interaction in one place Mephenytoin supplement interactions › Every supplement checked against Mephenytoin, ranked by severity 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 Guarana and Mephenytoin Together: Common Questions

Can you take Guarana with Mephenytoin?
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 Guarana and Mephenytoin 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 Mephenytoin and Guarana?

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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.