Drug & supplement interaction

Black Seed + Hydrochlorothiazide, Valsartan

Hydrochlorothiazide, Valsartan brand name: Diovan HCT.

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

Hydrochlorothiazide, Valsartan falls into 3 drug categories that Black Seed can interact with; the most serious is rated moderate. Theoretically, taking black seed with antihypertensive drugs might increase the risk of hypotension.

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

Black Seed and Hydrochlorothiazide, Valsartan

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. Hydrochlorothiazide, Valsartan 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

ANTIHYPERTENSIVE DRUGS

1 of 3

Why this applies to Hydrochlorothiazide, Valsartan

Hydrochlorothiazide, Valsartan falls under ANTIHYPERTENSIVE DRUGS — the group Black Seed interacts with.

Theoretically, taking black seed with antihypertensive drugs might increase the risk of hypotension.
Clinical research suggests that black seed powder and oil might reduce blood pressure by 2-3 mmHg. In animal research, black seed modestly reduces blood pressure and concomitant use of black seed and amlodipine (Norvasc) or metoprolol (Lopressor) increased the blood pressure lowering effects of these drugs.
Severity Moderate Likelihood Possible Evidence B

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 simple version: Diovan HCT already lowers your blood pressure, with the valsartan relaxing blood vessels and the hydrochlorothiazide (a water pill) helping you shed extra fluid and salt. Black seed appears to nudge blood pressure down a little too, on the order of 2 to 3 mmHg in studies. Stack the two together and the effects can add up, so your pressure could drop more than you expect.

If that happens, you might feel dizzy, lightheaded, or tired, especially when you stand up quickly. This is only a modest, possible effect, and the evidence is on the weaker side. Food-amounts of black seed as a spice are unlikely to matter, but concentrated supplements are. Please check with your pharmacist or doctor before adding it.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Dehkordi FR, Kamkhah AF. Antihypertensive effect of Nigella sativa seed extract in patients with mild hypertension. Fundam Clin Pharmacol 2008;22:447-52.
  2. Sahebkar A, Soranna D, Liu X, et al. A systematic review and meta-analysis of randomized controlled trials investigating the effects of supplementation with Nigella sativa (black seed) on blood pressure. J Hypertens 2016;34:2127-35. PubMed
  3. Alam MA, Bin Jardan YA, Raish M, Al-Mohizea AM, Ahad A, Al-Jenoobi FBI. Effect of Nigella sativa and fenugreek on the pharmacokinetics and pharmacodynamics of amlodipine in hypertensive rats. Curr Drug Metab. 2020;21(4):318-325. PubMed
  4. Bin Jardan YA, Ahad A, Raish M, Alam MA, Al-Mohizea AM, Al-Jenoobi FI. Effects of garden cress, fenugreek and black seed on the pharmacodynamics of metoprolol: an herb-drug interaction study in rats with hypertension. Pharm Biol 2021;59(1):1088-1097. PubMed
Moderate

DIURETIC DRUGS

2 of 3

Hydrochlorothiazide, Valsartan also falls under DIURETIC DRUGS.

Theoretically, taking black seed with diuretic drugs might increase potassium loss and the risk of hypokalemia.
Black seed extract has shown diuretic effects in animals, which could theoretically increase potassium loss. 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

Your Diovan HCT combo pill has two parts: valsartan, which relaxes blood vessels, and hydrochlorothiazide, a 'water pill' that helps your body shed extra fluid. One thing thiazide diuretics like the HCT portion can do is lower your potassium level over time. The concern on file is that black seed showed mild diuretic (fluid-losing) effects in animal studies, so in theory it might add to that potassium loss.

I want to be honest about how soft this evidence is, though. This has only been seen in lab and animal work, not in people, so it's more of a 'keep an eye out' than a real worry. If you ever feel unusually tired, crampy, weak, or notice an irregular heartbeat, check in with your pharmacist or doctor, and let them know about any black seed supplement before starting it.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Zaoui, A., Cherrah, Y., Lacaille-Dubois, M. A., Settaf, A., Amarouch, H., and Hassar, M. [Diuretic and hypotensive effects of Nigella sativa in the spontaneously hypertensive rat]. Therapie 2000;55(3):379-382.
Moderate

CYTOCHROME P450 2C9 (CYP2C9) SUBSTRATES

3 of 3

Hydrochlorothiazide, Valsartan 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 short version on combining black seed with your Diovan HCT (valsartan plus hydrochlorothiazide). The valsartan part is partly handled by a liver enzyme called CYP2C9. In a test-tube study, a black seed compound (thymoquinone) seemed to slow that enzyme down. If that happened in real life, valsartan could build up a bit, which theoretically might nudge your blood pressure lower than expected, leaving you dizzy or lightheaded, especially when standing up.

I want to be honest though: this is purely lab-based and has not been shown in people, so it's more of a maybe than a real worry. A pinch of black seed as a spice is very unlikely to matter. If you're using concentrated supplement doses, just give your pharmacist or doctor a heads-up first.

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

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 Hydrochlorothiazide, Valsartan 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. Hydrochlorothiazide, Valsartan)
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 Hydrochlorothiazide, Valsartan

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 Hydrochlorothiazide, Valsartan, 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 Hydrochlorothiazide, Valsartan

This page covers Black Seed only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Hydrochlorothiazide, Valsartan page lists 273 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), Asarabacca (major) and Dolomite (major).

By severity: 10 major · 226 moderate · 37 minor.

From our pharmacist’s overview on the Hydrochlorothiazide, Valsartan page

“Diovan HCT pairs valsartan with the water pill hydrochlorothiazide to bring blood pressure down, and the 273 supplements listed here deserve genuine care, ten of them rated major. Most of the moderate entries either drop blood pressure further than intended or blunt the medication, and a second large group compounds the diuretic action…”

Reviewed by 2 · Jul 18, 2026

Open the Hydrochlorothiazide, Valsartan 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 Hydrochlorothiazide, Valsartan 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 Hydrochlorothiazide, Valsartan 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%

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

29 days ago today
Medication Hydrochlorothiazide, Valsartan
Top 5%

#132 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 Hydrochlorothiazide, Valsartan, 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 Hydrochlorothiazide, Valsartan supplement interactions › Every supplement checked against Hydrochlorothiazide, Valsartan, 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 Hydrochlorothiazide, Valsartan Together: Common Questions

Can you take Black Seed with Hydrochlorothiazide, Valsartan?
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 Hydrochlorothiazide, Valsartan?
Hydrochlorothiazide, Valsartan 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 Hydrochlorothiazide, Valsartan 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 Hydrochlorothiazide, Valsartan 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.