Drug & supplement interaction

Grapefruit Diet + Oseltamivir Phosphate

Oseltamivir Phosphate brand name: Tamiflu.

No Known Interaction
Medically reviewed by · Updated June 2026 · Pair last verified Sep 20, 2026
The bottom line No known interaction

We found no known interaction between Grapefruit Diet and Oseltamivir Phosphate in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first.

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Interaction report

Grapefruit Diet and Oseltamivir Phosphate

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Oseltamivir Phosphate and Grapefruit Diet in our sources. This does not guarantee that the combination is completely free of risk — research on Grapefruit Diet alongside specific medications may be limited.

Worth understanding: our licensed dataset holds no drug-interaction record for Grapefruit Diet at all — not against Oseltamivir Phosphate, and not against any other medication we track. This verdict therefore rests on the absence of any recorded data, not on research that looked at this combination and found nothing. We cannot rule an interaction out.

Grapefruit Diet is an eating pattern rather than something you take. Ask your pharmacist or doctor before changing how you eat while on a prescribed medicine: some medicines are dosed around meals, and a change in diet can change how they work. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

Grapefruit Diet safety at a glance

Grapefruit Diet overall Use caution Grapefruit is a healthy food, but very low-calorie versions of this diet can be hard to sustain and grapefruit affects many medications.
Pregnancy Use caution Eating grapefruit as food is generally fine, but very low-calorie diets should be avoided during pregnancy.
Breastfeeding Use caution Grapefruit as food is usually fine, but restrictive dieting while breastfeeding is not recommended.

Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Oseltamivir Phosphate and Grapefruit Diet? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
What to actually watch for

What Oseltamivir Phosphate’s Own FDA Label Lists

This is not an interaction — none of it involves Grapefruit Diet. These are the most notable effects listed in the ADVERSE REACTIONS section of Oseltamivir Phosphate’s own FDA label, for the medication by itself. Knowing the drug’s own list makes it easier to work out the likely cause if something new turns up while you follow Grapefruit Diet and take the medicine. One of them is worth acting on rather than waiting out — marked below.

  • An allergic reaction Worth acting on
  • Vomiting mentioned in 8.6% of FDA reports for Oseltamivir Phosphate
  • Nausea mentioned in 6.5% of FDA reports for Oseltamivir Phosphate
  • Headache mentioned in 3.9% of FDA reports for Oseltamivir Phosphate

From the ADVERSE REACTIONS section of the FDA label for Oseltamivir Phosphate. Read the label on DailyMed › Where a percentage is shown, it is the share of 24,283 voluntary FDA FAERS reports for Oseltamivir Phosphate that mention that effect — a reporting proportion, not an incidence rate and not evidence the drug caused it. Grapefruit Diet’s licensed record lists no adverse effects our clinical vocabulary could match, so there is no Grapefruit Diet side to compare — that is a limit of the record, not a statement that Grapefruit Diet has no side effects.

From our Q&A

Questions About Grapefruit Diet or Oseltamivir 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 Diet or Oseltamivir 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 Oseltamivir Phosphate

This page covers Grapefruit Diet only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Oseltamivir Phosphate page lists 22 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), African Wild Potato (moderate), Banderol (moderate), Caffeic Acid (moderate) and Coffee Charcoal (moderate).

By severity: 1 major · 11 moderate · 10 minor.

From our pharmacist’s overview on the Oseltamivir Phosphate page

“Tamiflu (oseltamivir phosphate) only has about five days to do its job against the flu, so this list deserves a careful read, and the single major entry, activated charcoal, deserves it most. Charcoal can adsorb the drug and cut how much reaches your bloodstream, which is exactly what you cannot afford during a short antiviral course.”

Reviewed by 2 · Jul 18, 2026

Open the Oseltamivir Phosphate interaction page

How much people look this up

Where Grapefruit Diet and Oseltamivir 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 Diet
Steady interest

#1,124 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Oseltamivir Phosphate
Steady interest

#2,223 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.

Where does our data come from?
  • Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions. Grapefruit Diet is not yet covered by that licensed database, so its write-up cites publicly available medical sources directly (see the references below).
  • Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Grapefruit Diet reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 20, 2026. The Grapefruit Diet and Oseltamivir Phosphate records this page draws on were last updated June 22, 2026.
  • What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.
Data structure & sourcing designed and verified by .
Eating pattern

About Grapefruit Diet

What is Grapefruit Diet?

  • Weight loss
  • Appetite control
  • Short-term dieting
  • Blood sugar support
  • General 'detox' plans

The 'Grapefruit Diet' is a fad eating plan that pairs grapefruit or grapefruit juice with low-calorie meals, claiming the fruit burns fat. Any weight loss is most likely from cutting calories rather than a special fat-burning property of grapefruit. Grapefruit interacts with many medications, so talk to your pharmacist or doctor before starting.

Fruit and fruit juice (Citrus paradisi) · Fresh grapefruit, grapefruit juice, and as part of structured low-calorie meal plans; also grapefruit extract capsules sometimes marketed for weight loss

An interaction check asks whether these two react with each other — it does not ask whether Grapefruit Diet is a good idea for someone in your situation. Here is what our Grapefruit Diet record says about it on its own.

Grapefruit Diet: dosing

There is no standardized or medically established dose for the Grapefruit Diet. Plans typically suggest eating half a grapefruit or drinking a small glass of grapefruit juice with meals, but these amounts vary by version and are not based on solid research.If you choose to add grapefruit to your diet, a reasonable, food-based approach is far safer than a strict, very low-calorie plan.

From our Grapefruit Diet monograph — the full record covers uses, side effects and every documented interaction.

Read the full Grapefruit Diet monograph & all interactions
Medication

About Oseltamivir

What Is Oseltamivir Used For?

Brand name: Tamiflu

Oseltamivir is used to treat acute, uncomplicated influenza A and B in patients 2 weeks of age and older who have had symptoms for no more than 48 hours. It is also used to prevent (prophylaxis) influenza A and B in patients 1 year of age and older.

Keep in mind: oseltamivir is not a substitute for your annual flu vaccine. It does not work against bacterial infections or illnesses caused by anything other than influenza viruses.

Most-Reported Side Effects for Oseltamivir Phosphate

From FAERS, the FDA’s public side-effect reporting system (24,283 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Vomiting 2,082 reports
Nausea 1,575 reports
Influenza 1,197 reports
Diarrhea 1,044 reports
Dyspnea 1,012 reports
See full Oseltamivir drug information
Keep checking

Other Drugs & Grapefruit Diet

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

0Major
0Moderate
0Minor
2,829No known interaction
2,829 No interaction
No interaction 2,829 drugs checked — show the list

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

Showing the 60 most looked-up of 2,829 medications checked with no known interaction — see the full Grapefruit Diet list.

See the full Grapefruit Diet interactions page
See every supplement checked against Oseltamivir Phosphate, ranked by severity
Evidence & sources

Grapefruit Diet References

The 2 sources that drive our Grapefruit Diet monograph — publicly available pages from reputable medical and government organizations. Every link was verified to work before publishing. Grapefruit Diet is not covered by the licensed Natural Medicines interaction database, so its page cites these public sources directly.

  1. Grapefruit — MedlinePlus Source
  2. Choosing a Safe and Successful Weight-Loss Program — NIH NIDDK Source

Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Following Grapefruit Diet While Taking Oseltamivir Phosphate: Common Questions

Is it safe to follow Grapefruit Diet while taking Oseltamivir Phosphate?
We do not list a known interaction between Grapefruit Diet and Oseltamivir Phosphate. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.
Does Oseltamivir Phosphate interact with any supplements?
Yes. Oseltamivir Phosphate has documented interactions with 22 supplements in our database — Grapefruit Diet is not one of them. The Oseltamivir Phosphate interaction page linked on this page lists every one, ranked by severity.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Where next

Keep Exploring

Grapefruit Diet monograph Uses, safety profile, and every drug interaction in one place Oseltamivir drug information The full plain-English guide to this medication Oseltamivir Phosphate supplement interactions Every supplement checked against Oseltamivir Phosphate, 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 References The 2 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Oseltamivir Phosphate and Grapefruit Diet?

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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.