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Independent·Non-commercial·No products soldEducational only — not medical advice
Citrus paradisi seed (often adulterated)

Grapefruit seed extract

Grapefruit seed extract has no credible clinical evidence as a remedy, and the antimicrobial activity attributed to it has repeatedly been traced to synthetic preservatives added to commercial products, chiefly benzethonium chloride.

Laboratory analyses in several countries found these preservatives in most products tested, and one Swedish report linked such a product to a dangerous rise in INR in a patient taking warfarin. Treat it as an unreliable product of unknown composition rather than a herbal remedy.

Updated
10 October 2026
A halved pink grapefruit showing its seeds
At a glance
Last reviewed 10 October 2026
Evidence
Traditional
Best for
Antimicrobial use
Typical form & use
No studied form or dose
Onset
About a week
Safety
Often contains undeclared synthetic preservatives. 1 known interaction, most serious with blood thinners.
Check with your medications →

What it's used for

Evidence is rated per use. The same ingredient can be strong for one thing and traditional for another.

UseEvidenceWhat the research shows
Antimicrobial or immune supportTraditional

A 1999 German study found five of six commercial extracts inhibited bacteria and yeast, but all five contained benzethonium chloride, and the one extract without a preservative, plus home-made extracts from seed and pulp, showed no antimicrobial activity. The authors concluded the activity is due to the synthetic preservatives.

We found no human trial in this review that tests a verified preservative-free extract, so the rating rests on the traditional and marketing claim alone.1,2

Topical disinfectant or deodorantTraditional

Extracts are sold in disinfectant sprays, cosmetics and food preservatives. A Japanese survey using NMR and LC/MS found synthetic disinfectants (benzethonium or benzalkonium salts) in most commercial products across food additive, supplement, cosmetic and disinfectant categories. Any disinfecting effect of such a product is plausibly from the added chemical, not the grapefruit.3,4

How much

Ranges below are what studies used and what supplements commonly contain. They are not a recommendation for you. Start at the low end.

Studied range
None established1
We found no clinical trial or regulator monograph that sets a dose of a verified authentic extract, so no dose can be recommended.
Preservative content found
Benzethonium chloride up to 21.84%5,6
Avula et al. measured 0.29–21.84% benzethonium chloride in products labelled as grapefruit seed extract; Ganzera et al. found 2.5–176.9 mg/mL in specimens sold for eco-farming. A dose of the product is therefore also a dose of the preservative.
Timing · No source we read gives timing guidance, because there is no evidence-based dose.With food? · No source we read gives food guidance.How long to trial · There is no trial-based way to judge an effect. Given the contamination findings, we do not suggest trying it.

How people take it

Liquid concentrate (drops)Follow the label; not evidence-basedThree liquid products analysed after a warfarin adverse event contained benzethonium chloride, glycerol and water, and no authentic extract.
Capsule or supplementFollow the label; not evidence-basedIn one analysis of 17 commercial products, two contained benzethonium chloride, and many contained flavonoids suggesting peel or pulp rather than seed.
Spray or cosmetic ingredientNot applicableUsed as a disinfectant or preservative; the Japanese survey found synthetic disinfectants in most such products.

Safety

Who should avoid
  • People taking warfarin — a case report links a product to INR 7.9
  • Anyone taking CYP3A4 or CYP2C9 drugs — preservative inhibits both in vitro
  • Pregnancy and breastfeeding — no safety data, plus unlabelled preservatives
  • Anyone wanting a plant-only product — content is unreliable
Known interactions
CautionBlood thinners — A patient on warfarin developed an INR of 7.9 and a haematoma after taking a product, and the authors attribute it to the benzethonium chloride, which strongly inhibited CYP2C9 and CYP3A4 in vitro.

Questions people ask

Is grapefruit seed extract a natural antibiotic or antifungal?

The evidence says the antimicrobial effect comes from synthetic preservatives found in commercial products, not from the grapefruit. In a 1999 study, an extract without a preservative and home-made seed and pulp extracts showed no antimicrobial activity.

What is actually in grapefruit seed extract products?

Several analyses found benzethonium chloride, sometimes with triclosan, methylparaben or benzalkonium chloride. The share varies: two of 17 products in a 2016 analysis, seven of nine in a 2006 study, and most products in a Japanese survey.

Does grapefruit seed extract interact with medicines like grapefruit juice does?

The documented concern is different. A Swedish report linked a product's benzethonium chloride, not grapefruit compounds, to a raised INR in a patient on warfarin, and the preservative inhibited two liver enzymes in vitro. We did not find a source applying the grapefruit juice interaction to the seed extract.

Sources (7)

  1. Laboratory study von Woedtke T, Schlüter B, Pflegel P, Lindequist U, Jülich WD. Aspects of the antimicrobial efficacy of grapefruit seed extract and its relation to preservative substances contained. Pharmazie. 1999.
  2. Laboratory analysis Avula B, Sagi S, Wang YH, et al. Liquid chromatography-electrospray ionization mass spectrometry analysis of limonoids and flavonoids in seeds of grapefruits, other citrus species, and dietary supplements. Planta Med. 2016.
  3. Laboratory analysis Sugimoto N, Tada A, Kuroyanagi M, et al. Survey of synthetic disinfectants in grapefruit seed extract and its compounded products. Shokuhin Eiseigaku Zasshi. 2008.
  4. Laboratory analysis Bekiroglu S, Myrberg O, Ostman K, et al. Validation of a quantitative NMR method for suspected counterfeit products exemplified on determination of benzethonium chloride in grapefruit seed extracts. J Pharm Biomed Anal. 2008.
  5. Laboratory analysis Avula B, Dentali S, Khan IA. Simultaneous identification and quantification by liquid chromatography of benzethonium chloride, methyl paraben and triclosan in commercial products labeled as grapefruit seed extract. Pharmazie. 2007.
  6. Laboratory analysis Ganzera M, Aberham A, Stuppner H. Development and validation of an HPLC/UV/MS method for simultaneous determination of 18 preservatives in grapefruit seed extract. J Agric Food Chem. 2006.
  7. Case report and in vitro study Brandin H, Myrberg O, Rundlöf T, Arvidsson AK, Brenning G. Adverse effects by artificial grapefruit seed extract products in patients on warfarin therapy. Eur J Clin Pharmacol. 2007.

Reader notes

Experiences and questions from readers, read by an editor before they appear. They are personal accounts, not evidence, and are not medical advice.

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Last reviewed 10 October 2026 · Next review April 2027 · How we rate evidence