Drug & supplement interaction

Grape + Clozapine

Clozapine brand names: Clozaril, Versacloz.

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

Clozapine falls into 2 drug categories that Grape can interact with; the most serious is rated moderate. Theoretically, grape juice might reduce the levels of CYP1A2 substrates.

Read the full interaction report
SeverityModerate
LikelihoodPossible
Interactions2
EvidenceB
What do Severity, Likelihood & Evidence mean?
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Interaction report

Grape and Clozapine

These two interact in 2 distinct ways. Each one is explained separately below.

Why Are There 2 Interactions?

Grape interacts with whole categories of medication. Clozapine falls into 2 of those categories, so it can interact with Grape in 2 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Moderate).

Moderate

CYTOCHROME P450 1A2 (CYP1A2) SUBSTRATES

1 of 2

Why this applies to Clozapine

Clozapine falls under CYTOCHROME P450 1A2 (CYP1A2) SUBSTRATES — the group Grape interacts with.

Theoretically, grape juice might reduce the levels of CYP1A2 substrates.
A small pharmacokinetic study in healthy adults shows that ingestion of 200 mL of grape juice decreases phenacetin plasma levels. This is thought to be due to induction of CYP1A2.
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 gist for clozapine: your body relies on an enzyme called CYP1A2 to break this medicine down. Grape juice may gently speed that enzyme up. If clozapine clears a little faster, its blood levels could dip, and that can mean the drug works less well, so symptoms like disordered thinking might creep back. Clozapine is not a prodrug, so faster clearance simply means less effect, not more.

Honestly though, the evidence here is thin and mostly theoretical, based on a small study using a different drug. Clozapine also needs careful, steady dosing, so I wouldn't add or drop grape juice on a whim. Just loop in your pharmacist or prescriber before making any changes.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Xiao Dong S, Zhi Ping Z, Zhong Xiao W, et al. Possible enhancement of the first-pass metabolism of phenacetin by ingestion of grape juice in Chinese subjects. Br J Clin Pharmacol 1999;48:638-40. PubMed
Moderate

CYTOCHROME P450 2D6 (CYP2D6) SUBSTRATES

2 of 2

Clozapine also falls under CYTOCHROME P450 2D6 (CYP2D6) SUBSTRATES.

Theoretically, grape seed extract may increase the levels of CYP2D6 substrates.
In vitro evidence suggests that grape seed extract might inhibit CYP2D6 enzymes. However, this interaction has not been reported 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 for clozapine and grape seed extract. Lab studies hint that grape seed extract might block an enzyme called CYP2D6, which is one of the pathways your body uses to clear clozapine. If that enzyme slows down, clozapine could build up a little more than expected. Since clozapine is an active drug (not a prodrug), more of it in your system could mean stronger side effects like heavy sedation, dizziness, drooling, constipation, a faster heartbeat, or low blood pressure.

That said, this is only a theoretical concern seen in test-tube studies, never actually reported in real patients. Eating grapes is fine. Before starting a concentrated grape seed supplement, though, check with your pharmacist or doctor, since clozapine is a drug that needs careful monitoring.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Nishikawa, M., Ariyoshi, N., Kotani, A., Ishii, I., Nakamura, H., Nakasa, H., Ida, M., Nakamura, H., Kimura, N., Kimura, M., Hasegawa, A., Kusu, F., Ohmori, S., Nakazawa, K., and Kitada, M. Effects of continuous ingestion of green tea or grape seed extra

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

Grape Also Interacts With Other Medications

Grape has 867 moderate, 42 minor known drug interactions in our database — the Clozapine one above is among them. If you take anything else, check it against the full list below.

Moderate 867 Minor 42 No known interaction 1,921 (incl. Clozapine)
Taking anything else?

Check Another of Your Medications Against Grape

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

From our Q&A

Questions About Grape or Clozapine

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

This page covers Grape only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Clozapine page lists 212 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Henbane (major), Indian Snakeroot (major), Lithium (major) and Rauvolfia Vomitoria (major).

By severity: 6 major · 164 moderate · 42 minor.

From our pharmacist’s overview on the Clozapine page

“Clozapine (Clozaril, Versacloz) is usually the last-resort antipsychotic for schizophrenia, prescribed under close monitoring because small shifts in its blood level matter, so the 212 supplement interactions on file here deserve genuine care rather than a quick skim. Six are rated major.”

Reviewed by 2 · Jul 18, 2026

Open the Clozapine interaction page

One more smart check

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

We hold 8,053 real supplement products containing Grape, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Grape. Your product may carry other ingredients that interact with Clozapine too, on top of Grape — 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 Grape and Clozapine 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 Grape
Top 5%

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

29 days ago today
Medication Clozapine
Steady interest

#1,562 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 Grape

What is Grape?

Grape
  • Antioxidant support
  • Heart and circulation health
  • Vein problems (such as varicose veins)
  • Eye health
  • General anti-inflammatory support

Grapes and grape products like grape seed extract contain antioxidant compounds such as resveratrol and proanthocyanidins that may support heart and blood vessel health. While the food is healthy and generally safe, the supplement evidence for treating specific conditions is mostly limited or preliminary. Talk with your pharmacist or doctor before starting a grape supplement.

Read the full Grape monograph & all interactions
Medication

About Clozapine

What Is Clozapine Used For?

Brand names: Clozaril, Versacloz

Clozapine is used for two specific situations. First, it is prescribed for people with severe schizophrenia who have already tried other antipsychotic medications and have not gotten adequate relief. It is reserved for this group because of its serious risks.

Second, clozapine is used to lower the chances of repeated suicidal behavior in people with schizophrenia or schizoaffective disorder who are considered to be at ongoing, chronic risk. It is not a first-choice medication — it is used when the need is serious and other options have fallen short.

See full Clozapine drug information
Keep checking

Other Drugs & Grape

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

0Major
867Moderate
42Minor
1,920No known interaction
867 Moderate 42 Minor 1,920 No interaction
Moderate

867 interactions

Showing 60 of 867 moderate interactions — see all 867 on the Grape page.

Minor

42 interactions

No interaction 1,920 drugs checked — show the list

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

Showing the 60 most looked-up of 1,920 medications checked with no known interaction — see the full Grape list.

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

Can you take Grape with Clozapine?
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 2 interactions listed for Grape and Clozapine?
Clozapine belongs to more than one drug category, and Grape 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 Grape and Clozapine 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 Clozapine and Grape?

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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.