Drug & supplement interaction

Black Seed + Mephenytoin

Mephenytoin brand name: Mesantoin.

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

Mephenytoin falls into 3 drug categories that Black Seed can interact with; the most serious is rated moderate. Theoretically, concomitant use with drugs that have sedative properties may cause additive effects.

Read the full interaction report
SeverityModerate
LikelihoodPossible
Interactions3
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Black Seed and Mephenytoin

These two interact in 3 distinct ways. Each one is explained separately below.

Why Are There 3 Interactions?

Black Seed interacts with whole categories of medication. Mephenytoin falls into 3 of those categories, so it can interact with Black Seed in 3 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Moderate).

Moderate

CNS DEPRESSANTS

1 of 3

Why this applies to Mephenytoin

Mephenytoin falls under CNS DEPRESSANTS — the group Black Seed interacts with.

Theoretically, concomitant use with drugs that have sedative properties may cause additive effects.
Animal research suggests that black seed may have CNS depressant effects.
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

Mephenytoin (Mesantoin) is an older seizure medicine, and like many anti-seizure drugs it can already leave you feeling drowsy, foggy, or unsteady on your feet. Black seed, based mostly on animal and lab studies, may have its own mild calming or sedating effect on the brain. So the worry here is simple: taking the two together could stack those effects and make you sleepier or more lightheaded than usual.

I want to be honest with you, though. This interaction is theoretical and hasn't been clearly shown in people, so it's a possible concern rather than a proven one. Small amounts of black seed used as a kitchen spice are unlikely to matter much. Concentrated supplement doses are the bigger question mark. Please check with your pharmacist or doctor before adding it.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Al Naggar, T. B., Gomez-Serranillos, M. P., Carretero, M. E., and Villar, A. M. Neuropharmacological activity of Nigella sativa L. extracts. J Ethnopharmacol. 2003;88(1):63-68. PubMed
Moderate

CYTOCHROME P450 2C9 (CYP2C9) SUBSTRATES

2 of 3

Mephenytoin also falls under CYTOCHROME P450 2C9 (CYP2C9) SUBSTRATES.

Theoretically, black seed might increase levels of drugs metabolized by CYP2C9.
In vitro research suggests that thymoquinone, a constituent of black seed, can decrease the metabolism of phenytoin by a mechanism possibly related to the inhibition of CYP2C9. The effect of black seed on CYP2C9 is unclear. This has not been shown in humans.
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: your body clears mephenytoin partly through a liver enzyme called CYP2C9. In test-tube studies, a compound in black seed (thymoquinone) seemed to slow that same enzyme down. If that held true in people, mephenytoin could build up in your system and push you toward more side effects, things like drowsiness, dizziness, unsteady walking, slurred speech, or double vision.

I want to be honest, though: this is purely theoretical. It has only been seen in lab dishes, never confirmed in actual patients, and the real effect is unclear. Because seizure medicines like mephenytoin have a narrow safety window where small changes matter, I'd still flag it. Cooking with the spice is unlikely to be an issue, but check with your pharmacist or doctor before using concentrated black seed supplements.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Wang Z, Wang X, Wang Z, et al. Potential herb-drug interaction risk of thymoquinone and phenytoin. Chem Biol Interact. 2022;353:109801. PubMed
Moderate

PHENYTOIN (Dilantin)

3 of 3
Theoretically, black seed might increase or decrease levels and effects of phenytoin.
In vitro research suggests that thymoquinone, a constituent of black seed, can decrease the metabolism of phenytoin. This effect may be due to inhibition of cytochrome P450 2C9 (CYP2C9). However, animal research shows that black seed decreases the maximum concentration of and total systemic exposure to phenytoin by 57% and 87%, respectively. This seems to be related to increased clearance and steady state volume of distribution. This interaction has not been shown in humans.
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 honest picture with black seed and mephenytoin. Mephenytoin is an older anti-seizure drug, and like its cousin phenytoin, it has a narrow safety window, meaning small shifts in its blood level can tip you toward either more side effects or weaker seizure control. The tricky part is that black seed could pull in either direction. Lab studies hint that thymoquinone (its active compound) may slow the enzyme that clears this drug, which would raise levels. But animal studies showed the opposite, with black seed actually lowering drug levels quite a bit.

If levels rose, you might see more dizziness, drowsiness, unsteadiness, or trouble with coordination; if they dropped, your seizures could become less controlled. The good news: this has only been seen in test tubes and animals, never in people, so don't panic. Food-amount spice is unlikely to matter, but please check with your pharmacist or doctor before using concentrated black seed supplements.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Wang Z, Wang X, Wang Z, et al. Potential herb-drug interaction risk of thymoquinone and phenytoin. Chem Biol Interact. 2022;353:109801. PubMed
  2. Alkharfy KM, Al-Jenoobi FI, Al-Mohizea AM, et al. Effects of Lepidium sativum, Nigella sativa and Trigonella foenum-graceum on phenytoin pharmacokinetics in beagle dogs. Phytother Res. 2013;27(12):1800-4.

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

Black Seed Also Interacts With Other Medications

Black Seed has 911 moderate known drug interactions in our database — the Mephenytoin one above is among them. If you take anything else, check it against the full list below.

Moderate 911 No known interaction 1,919 (incl. Mephenytoin)
Taking anything else?

Check Another of Your Medications Against Black Seed

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

From our Q&A

Questions About Black Seed or Mephenytoin

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Black Seed or Mephenytoin, 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 Mephenytoin

This page covers Black Seed 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 Black Seed as Part of a Dietary Supplement Product? Check It for Interactions

We hold 226 real supplement products containing Black Seed, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Black Seed. Your product may carry other ingredients that interact with Mephenytoin too, on top of Black Seed — 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 Black Seed 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 Black Seed
Top 25%

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

29 days ago today
Medication Mephenytoin
Steady interest

#2,315 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 Black Seed

What is Black Seed?

Black Seed
  • Respiratory support (asthma, allergies, cough)
  • Digestive upset
  • Immune support
  • Blood sugar and cholesterol support
  • General inflammation

Black seed (Nigella sativa) is a traditional spice and remedy that has been studied for asthma, blood sugar, cholesterol, and blood pressure, with early research showing some promise but no firmly proven benefits. It is generally well tolerated in food amounts, but supplement-strength doses are less studied, so talk to your pharmacist or doctor before using it—especially if you are pregnant, breastfeeding, or take other medicines.

Read the full Black Seed monograph & all interactions
Keep checking

Other Drugs & Black Seed

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

0Major
911Moderate
0Minor
1,918No known interaction
911 Moderate 1,918 No interaction
Moderate

911 interactions

Showing 60 of 911 moderate interactions — see all 911 on the Black Seed page.

No interaction 1,918 drugs checked — show the list

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

Showing the 60 most looked-up of 1,918 medications checked with no known interaction — see the full Black Seed list.

See the full Black Seed 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
Black Seed 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 Black Seed and Mephenytoin Together: Common Questions

Can you take Black Seed 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.
Why are there 3 interactions listed for Black Seed and Mephenytoin?
Mephenytoin belongs to more than one drug category, and Black Seed 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 Black Seed 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 Black Seed?

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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.