Drug & supplement interaction

Hibiscus Sabdariffa + Phenobarbital, Phenytoin

Phenobarbital, Phenytoin brand name: Dilantin with PB.

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

Phenobarbital, Phenytoin falls into 4 drug categories that Hibiscus Sabdariffa can interact with; the most serious is rated minor. Theoretically, Hibiscus sabdariffa extract might reduce the metabolism of CYP2C19 substrates.

Read the full interaction report
SeverityMinor
LikelihoodPossible
Interactions4
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Hibiscus Sabdariffa and Phenobarbital, Phenytoin

These two interact in 4 distinct ways. Each one is explained separately below.

Why Are There 4 Interactions?

Hibiscus Sabdariffa interacts with whole categories of medication. Phenobarbital, Phenytoin falls into 4 of those categories, so it can interact with Hibiscus Sabdariffa in 4 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Minor).

Minor

CYTOCHROME P450 2C19 (CYP2C19) SUBSTRATES

1 of 4

Why this applies to Phenobarbital, Phenytoin

Phenobarbital, Phenytoin falls under CYTOCHROME P450 2C19 (CYP2C19) SUBSTRATES — the group Hibiscus Sabdariffa interacts with.

Theoretically, Hibiscus sabdariffa extract might reduce the metabolism of CYP2C19 substrates.
In vitro research shows that Hibiscus sabdariffa calyx extract inhibits CYP2C19. This interaction has not been reported in humans.
Severity Minor 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: phenytoin (often combined with phenobarbital in Dilantin with PB) is partly cleared by a liver enzyme called CYP2C19. Lab studies in a test tube suggest hibiscus may slow that enzyme down a bit. If that happened in your body, phenytoin could clear a little slower and drift higher, which can show up as drowsiness, dizziness, unsteady walking, slurred speech, or jerky eye movements.

The important part is that this is purely theoretical. It has never actually been reported in people, and an occasional cup of tart hibiscus tea is very unlikely to matter. Still, phenytoin is a tricky drug where small swings count, so if you plan to use concentrated hibiscus supplements regularly, run it by your pharmacist or doctor first.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Johnson SS, Oyelola FT, Ari T, Juho H. In vitro inhibitory activities of the extract of Hibiscus sabdariffa L. (family Malvaceae) on selected cytochrome P450 isoforms. Afr J Tradit Complement Altern Med. 2013 Apr 12;10(3):533-40.
Minor

CYTOCHROME P450 2C9 (CYP2C9) SUBSTRATES

2 of 4

Phenobarbital, Phenytoin also falls under CYTOCHROME P450 2C9 (CYP2C9) SUBSTRATES.

Theoretically, Hibiscus sabdariffa extract might reduce the metabolism of CYP2C9 substrates.
In vitro research shows that Hibiscus sabdariffa calyx extract inhibits CYP2C9. This interaction has not been reported in humans.
Severity Minor 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 for your phenytoin (the Dilantin part of this combo). Your liver uses an enzyme called CYP2C9 to break phenytoin down. In a test-tube study, hibiscus appeared to slow that enzyme a little. If that held true in people, phenytoin might clear a touch more slowly and build up, which could nudge you toward side effects like dizziness, drowsiness, unsteady walking, slurred speech, or jerky eye movements.

That said, this is purely theoretical. It has never actually been seen in a real patient, and a cup of tart hibiscus tea is unlikely to matter. Phenytoin is a finicky drug where small swings count, so before starting a concentrated hibiscus supplement, just run it by your pharmacist or doctor first.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Johnson SS, Oyelola FT, Ari T, Juho H. In vitro inhibitory activities of the extract of Hibiscus sabdariffa L. (family Malvaceae) on selected cytochrome P450 isoforms. Afr J Tradit Complement Altern Med. 2013 Apr 12;10(3):533-40.
Minor

CYTOCHROME P450 2C8 (CYP2C8) SUBSTRATES

3 of 4

Phenobarbital, Phenytoin also falls under CYTOCHROME P450 2C8 (CYP2C8) SUBSTRATES.

Theoretically, Hibiscus sabdariffa might reduce the metabolism of CYP2C8 substrates.
In vitro research shows that Hibiscus sabdariffa calyx extract inhibits CYP2C8. This interaction has not been reported in humans.
Severity Minor 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 for this combo: lab studies suggest hibiscus may slow down an enzyme called CYP2C8. In theory, if that enzyme helps clear your medicine, the drug could build up a bit. With phenytoin especially, that matters because it's a narrow therapeutic index drug, meaning the gap between a helpful dose and a too-high dose is small. Higher phenytoin levels can show up as dizziness, unsteady walking, slurred speech, or feeling extra drowsy, and phenobarbital can add to that sleepiness.

That said, this is only seen in test-tube research, never reported in real people, and it's rated minor. A cup of tart hibiscus tea is unlikely to cause trouble. Still, before using a concentrated hibiscus supplement, please check with your pharmacist or doctor.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Johnson SS, Oyelola FT, Ari T, Juho H. In vitro inhibitory activities of the extract of Hibiscus sabdariffa L. (family Malvaceae) on selected cytochrome P450 isoforms. Afr J Tradit Complement Altern Med. 2013 Apr 12;10(3):533-40.
Minor

CYTOCHROME P450 2B6 (CYP2B6) SUBSTRATES

4 of 4

Phenobarbital, Phenytoin also falls under CYTOCHROME P450 2B6 (CYP2B6) SUBSTRATES.

Theoretically, Hibiscus sabdariffa extract might reduce the metabolism of CYP2B6 substrates.
In vitro research shows that Hibiscus sabdariffa calyx extract inhibits CYP2B6. This interaction has not been reported in humans.
Severity Minor 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 for this combo. In a lab dish, hibiscus extract appears to slow down an enzyme called CYP2B6, which helps your body break down phenobarbital. If that enzyme is blocked, phenobarbital could theoretically build up a bit and lead to more of its usual effects, like drowsiness, dizziness, or feeling unsteady. Phenobarbital has a fairly narrow safe range, so I never take changes lightly.

That said, this is only a theoretical concern from test-tube data, and it has never actually been reported in people. Everyday hibiscus tea is unlikely to be an issue. If you're using concentrated hibiscus supplements regularly, just give your pharmacist or doctor a heads-up first.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Johnson SS, Oyelola FT, Ari T, Juho H. In vitro inhibitory activities of the extract of Hibiscus sabdariffa L. (family Malvaceae) on selected cytochrome P450 isoforms. Afr J Tradit Complement Altern Med. 2013 Apr 12;10(3):533-40.

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

Hibiscus Sabdariffa Also Interacts With Other Medications

Hibiscus Sabdariffa has 2 major, 266 moderate, 820 minor known drug interactions in our database — the Phenobarbital, Phenytoin one above is among them. If you take anything else, check it against the full list below.

Major 2 Moderate 266 Minor 820 No known interaction 1,742 (incl. Phenobarbital, Phenytoin)
Taking anything else?

Check Another of Your Medications Against Hibiscus Sabdariffa

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

Everything else you take

See Every Supplement That Interacts With Phenobarbital, Phenytoin

This page covers Hibiscus Sabdariffa only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Phenobarbital, Phenytoin page lists 229 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 · 192 moderate · 28 minor.

From our pharmacist’s overview on the Phenobarbital, Phenytoin page

“If your seizure medicine is the phenobarbital and phenytoin combination (Dilantin with PB), read this list carefully before you add any supplement. Nine of the 229 entries rate major, and most of the risk runs through two channels.”

Reviewed by 2 · Jul 18, 2026

Open the Phenobarbital, Phenytoin interaction page

How much people look this up

Where Hibiscus Sabdariffa and Phenobarbital, Phenytoin 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 Hibiscus Sabdariffa
Top half

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

29 days ago today
Medication Phenobarbital, Phenytoin
Top 25%

#388 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 Hibiscus Sabdariffa

What is Hibiscus Sabdariffa?

Hibiscus Sabdariffa
  • High blood pressure
  • Heart and cholesterol health
  • Digestive upset
  • Antioxidant support
  • Fever and general wellness

Hibiscus sabdariffa is a tart, cranberry-flavored plant most often consumed as a tea, and its best-studied use is for mildly lowering blood pressure. Evidence for other uses is limited, and while hibiscus tea is generally well tolerated in food amounts, concentrated supplements should be used cautiously and avoided in pregnancy. Talk to your pharmacist or doctor before using it for a medical condition.

Read the full Hibiscus Sabdariffa monograph & all interactions
Keep checking

Other Drugs & Hibiscus Sabdariffa

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

2Major
266Moderate
820Minor
1,741No known interaction
2 Major 266 Moderate 820 Minor 1,741 No interaction
Major

2 interactions

Moderate

266 interactions

Showing 60 of 266 moderate interactions — see all 266 on the Hibiscus Sabdariffa page.

Minor

820 interactions

Showing 60 of 820 minor interactions — see all 820 on the Hibiscus Sabdariffa page.

No interaction 1,741 drugs checked — show the list

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

Showing the 60 most looked-up of 1,741 medications checked with no known interaction — see the full Hibiscus Sabdariffa list.

See the full Hibiscus Sabdariffa interactions page
See every supplement checked against Phenobarbital, Phenytoin, 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
Hibiscus Sabdariffa monograph › Uses, safety, and every drug interaction in one place Phenobarbital, Phenytoin supplement interactions › Every supplement checked against Phenobarbital, Phenytoin, 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 Hibiscus Sabdariffa and Phenobarbital, Phenytoin Together: Common Questions

Can you take Hibiscus Sabdariffa with Phenobarbital, Phenytoin?
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 4 interactions listed for Hibiscus Sabdariffa and Phenobarbital, Phenytoin?
Phenobarbital, Phenytoin belongs to more than one drug category, and Hibiscus Sabdariffa 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 Hibiscus Sabdariffa and Phenobarbital, Phenytoin 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

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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.