Drug & supplement interaction

Grapefruit + Primaquine Phosphate

Primaquine Phosphate brand name: Primaquine.

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

Grapefruit has a moderate interaction with Primaquine Phosphate. Grapefruit juice may increase blood levels of primaquine, potentially increasing the effects and adverse effects of primaquine.

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

Grapefruit and Primaquine Phosphate

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

Moderate

PRIMAQUINE

Grapefruit juice may increase blood levels of primaquine, potentially increasing the effects and adverse effects of primaquine.
Clinical research shows that grapefruit juice increases the bioavailability of primaquine by approximately 20%. The clinical significance of this interaction is not clear.
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 short version: when you drink grapefruit juice while taking primaquine, your body seems to absorb a bit more of the drug. In one clinical study, grapefruit juice raised primaquine levels by roughly 20 percent. That's a modest bump, and honestly the researchers weren't sure how much it matters in real life.

Still, more drug in your system can mean more of primaquine's usual effects, including stomach upset, nausea, headache, or in rare cases changes to your blood (especially if you have a G6PD deficiency, which your doctor should check before starting). I wouldn't panic over an occasional half grapefruit, but I'd avoid making grapefruit juice a daily habit while on this. Please check with your pharmacist or doctor before mixing the two regularly.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Cuong, B. T., Binh, V. Q., Dai, B., Duy, D. N., Lovell, C. M., Rieckmann, K. H., and Edstein, M. D. Does gender, food or grapefruit juice alter the pharmacokinetics of primaquine in healthy subjects? Br J Clin Pharmacol 2006;61(6):682-689. 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

Grapefruit Also Interacts With Other Medications

Grapefruit has 776 major, 150 moderate, 63 minor known drug interactions in our database — the Primaquine Phosphate one above is one of them. If you take anything else, check it against the full list below.

Major 776 Moderate 150 Minor 63 No known interaction 1,841 (incl. Primaquine Phosphate)
Taking anything else?

Check Another of Your Medications Against Grapefruit

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

From our Q&A

Questions About Grapefruit or Primaquine Phosphate

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

This page covers Grapefruit only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Primaquine Phosphate page lists 18 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Coffee Charcoal (moderate), European Mandrake (moderate), Glucomannan (moderate) and Guar Gum (moderate).

By severity: 1 major · 8 moderate · 9 minor.

From our pharmacist’s overview on the Primaquine Phosphate page

“Activated charcoal, the only major-rated interaction among the 18 on file, can bind primaquine phosphate (Primaquine) in the gut and shrink how much of each dose your body actually absorbs. That matters more than usual, because this antimalarial exists to wipe out the malaria parasites hiding in the liver, and an under-absorbed course…”

Reviewed by 2 · Jul 18, 2026

Open the Primaquine Phosphate interaction page

One more smart check

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

We hold 1,144 real supplement products containing Grapefruit, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Grapefruit. Your product may carry other ingredients that interact with Primaquine Phosphate too, on top of Grapefruit — 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 Grapefruit and Primaquine Phosphate 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 Grapefruit
Top 10%

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

29 days ago today
Medication Primaquine Phosphate
Steady interest

#2,506 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 Grapefruit

What is Grapefruit?

Grapefruit
  • Source of vitamin C
  • Digestive complaints
  • Antimicrobial (seed extract)
  • Weight management
  • Skin and cosmetic uses

Grapefruit is a nutritious citrus fruit rich in vitamin C and other nutrients, and it is generally safe to eat. However, grapefruit is famous for serious interactions with many prescription medicines, so anyone taking medication should check with a pharmacist or doctor before consuming it regularly.

Read the full Grapefruit monograph & all interactions
Medication

About Primaquine

What Is Primaquine Used For?

Brand name: Primaquine

Primaquine Phosphate Tablets are used for the radical cure of vivax malaria — meaning they target and eliminate the dormant liver forms of the Plasmodium vivax parasite that can cause the infection to come back (relapse). This is different from treating the active blood-stage infection, which is usually handled first with another medicine like chloroquine.

Primaquine Phosphate Tablets are also used after a course of chloroquine suppressive therapy in areas where vivax malaria is common, to prevent relapse once that preventive treatment ends.

See full Primaquine drug information
Keep checking

Other Drugs & Grapefruit

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

776Major
150Moderate
63Minor
1,840No known interaction
776 Major 150 Moderate 63 Minor 1,840 No interaction
Major

776 interactions

Showing 60 of 776 major interactions — see all 776 on the Grapefruit page.

Moderate

150 interactions

Showing 60 of 150 moderate interactions — see all 150 on the Grapefruit page.

Minor

63 interactions

Showing 60 of 63 minor interactions — see all 63 on the Grapefruit page.

No interaction 1,840 drugs checked — show the list

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

Showing the 60 most looked-up of 1,840 medications checked with no known interaction — see the full Grapefruit list.

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

Can you take Grapefruit with Primaquine Phosphate?
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 Grapefruit and Primaquine Phosphate 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 Primaquine Phosphate and Grapefruit?

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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.