Grapefruit
EVIDENCE: WEAKAlso sold as: Citrus paradisi, grapefruit seed extract, GSE, grapefruit fruit extract
Fresh grapefruit eaten before meals produced small weight loss and better insulin readings in one 12-week trial. Grapefruit seed extract is a different product with a history of synthetic preservative contamination. Grapefruit juice interacts with many prescription drugs.
Compiled by iSupplementReviews editorial team ·Researched 2026-10-16 · 4 sources
- Type
- Botanical fruit/seed extract
- Studied dose
- Half a fresh grapefruit or 8 oz juice before meals (weight trial)
- Best form
- whole fruit for the studied effect; seed extracts are not comparable
- Our rating
- WEAK — Mostly small, animal, or traditional evidence
What is grapefruit?
Grapefruit (Citrus paradisi) is a citrus fruit; supplements use either fruit extract or grapefruit seed extract, which are very different products. Most human research is on the whole fruit and juice.
Other names and forms
Grapefruit fruit extract, grapefruit seed extract (GSE), citrus seed extract, naringin (a grapefruit flavonoid).
Where does grapefruit come from?
A subtropical citrus tree. Seed extract is made from seeds, pulp and membranes.
How does grapefruit work in the body?
Grapefruit’s furanocoumarins block the CYP3A4 enzyme in the gut wall, which is why it raises blood levels of many drugs. Any weight effect from the whole fruit may partly come from its fiber and water filling people up before meals.
What is grapefruit claimed to do?
Aid weight loss, steady blood sugar, and (for seed extract) fight microbes.
What does the research show?
| Claim | Evidence | Dose studied | Verdict |
|---|---|---|---|
| Weight and insulin (fresh fruit) | One 12-week RCT | Half a grapefruit before meals | Small positive |
| Antimicrobial (seed extract) | Activity linked to added preservatives | — | Unreliable |
| Glucose from extracts | No human trials | — | Insufficient |
Weight and insulin
Fresh grapefruit before meals produced small weight loss in one trial. Fujioka et al. (2006) randomized 91 obese adults; the fresh-fruit group lost about 1.6 kg over 12 weeks versus 0.3 kg on placebo, with improved insulin resistance.
Seed extract quality
Commercial grapefruit seed extracts have repeatedly tested positive for synthetic preservatives. Avula et al. (2007) found benzethonium chloride and other preservatives in products labeled as grapefruit seed extract. Brandin et al. (2007) linked such products to bleeding events in patients on warfarin.
What dose was studied?
| Goal | Dose | Duration |
|---|---|---|
| Weight and insulin | Half a fresh grapefruit or 8 oz juice before meals | 12 weeks |
Side effects
The fruit is a common food. Seed extracts carry contamination concerns.
Drug interactions
- Many prescription drugs (some statins, calcium-channel blockers, antiarrhythmics, immunosuppressants): grapefruit can raise blood levels sharply (major; Bailey et al., 2013).
- Warfarin: case reports with seed-extract products (moderate).
Who should not take grapefruit products?
Anyone on a drug with a grapefruit warning on its label.
What the authorities say
Drug regulators require grapefruit warnings on many prescription labels. No authority recognizes grapefruit extracts for weight or glucose control.
What to know about grapefruit
The weight evidence is for fresh grapefruit, not extracts, and the effect was small. Seed extracts are a separate product with a contamination record.
Frequently asked questions about Grapefruit
Does grapefruit help weight loss?
Slightly, in one trial. Eating half a fresh grapefruit before meals for 12 weeks led to about 1.6 kg of weight loss versus 0.3 kg with placebo, and better insulin resistance. Extract supplements were not what was tested.
Is grapefruit seed extract the same as grapefruit?
No. Grapefruit seed extract is made from seeds and pulp, and several lab analyses found commercial products contained synthetic preservatives such as benzethonium chloride.
Does grapefruit interact with medicines?
Grapefruit juice and fruit block an enzyme (CYP3A4) that breaks down many drugs, including some statins, blood-pressure and heart-rhythm drugs. Whether small extract amounts do the same depends on their furanocoumarin content, which labels rarely state.
References
- [1]Fujioka K et al. — The effects of grapefruit on weight and insulin resistance: relationship to the metabolic syndrome (J Med Food, 2006)
- [2]Bailey DG et al. — Grapefruit-medication interactions: forbidden fruit or avoidable consequences? (CMAJ, 2013)
- [3]Avula B et al. — Simultaneous identification and quantification by liquid chromatography of benzethonium chloride, methyl paraben and triclosan in commercial products labeled as grapefruit seed extract (Pharmazie, 2007)
- [4]Brandin H et al. — Adverse effects by artificial grapefruit seed extract products in patients on warfarin therapy (Eur J Clin Pharmacol, 2007)
Products we reviewed containing Grapefruit
Based on recorded labels or seller-described formulas. Inclusion does not establish a match to the strains, preparations or amounts studied here; check each review's disclosure limits.