Grapefruit
A nutritious citrus food and the textbook food-drug interaction. Grapefruit irreversibly inhibits intestinal CYP3A4 — a single glass can boost the blood level of dozens of common drugs (statins, calcium channel blockers, tacrolimus, buspirone, many others) for 24+ hours, sometimes dangerously. As a food it provides vitamin C, fiber, lycopene, and carotenoids. Weight-loss supplement claims are weakly supported and not specific to grapefruit.
Quick decision guide
May help most
People not on interacting medications who enjoy citrus and want a high-vitamin-C, low-calorie fruit. NOT a worthwhile choice if you're on any drug listed in the safety section — switch to oranges instead.
Common dosing range
Half a medium grapefruit or ~150 mL juice as part of a meal. ANY amount can fully inhibit intestinal CYP3A4 in sensitive people, so 'a small glass is safe' is wrong for the high-risk drugs.
When to expect effects
Drug-interaction effect is immediate and lasts 24–72 hours from a single serving. Nutritional benefits are continuous with regular intake.
Watch out for
Always ask a pharmacist about grapefruit interactions for every new prescription. If you take simvastatin, lovastatin, atorvastatin, felodipine, nifedipine, tacrolimus, cyclosporine, amiodarone, buspirone, or many cancer/HIV drugs — avoid grapefruit (and Seville oranges, pomelos, tangelos) entirely.
Evidence snapshot
What is it
Grapefruit is a plant-derived ingredient sold as a dietary supplement and used in traditional herbal use. Found on roughly 1,232 U.S. supplement labels.
Is it worth it for you?
Use this as a quick fit check, not a diagnosis.
Worth considering if…
Probably skip if…
Evidence at a glance
| Goal | Effect | Best fit | Time |
|---|---|---|---|
Vitamin C and fiber from a low-calorie fruit Strong Evidence | ~47% DV vitamin C + 2 g fiber per half grapefruit (~50 kcal) | Adults wanting a low-calorie source of vitamin C, fiber, and carotenoids — and who don't take grapefruit-sensitive drugs | Vitamin C status improves within days; nutrition benefit is continuous with intake |
Modest weight loss (whole fruit pre-meal) Limited Evidence | Pre-meal half grapefruit produced ~1.3 kg additional weight loss in one 12-week RCT; not replicated with concurrent calorie restriction | Adults using whole grapefruit pre-meal as part of a calorie-controlled diet | Weeks (12-week trial endpoints) |
Modest improvement in HDL cholesterol Limited Evidence | Small HDL increases of a few mg/dL across 12-week trials | Adults using grapefruit as part of a broader heart-healthy diet | Weeks |
Vitamin C and fiber from a low-calorie fruit
- Effect
- ~47% DV vitamin C + 2 g fiber per half grapefruit (~50 kcal)
- Best fit
- Adults wanting a low-calorie source of vitamin C, fiber, and carotenoids — and who don't take grapefruit-sensitive drugs
- Time
- Vitamin C status improves within days; nutrition benefit is continuous with intake
Modest weight loss (whole fruit pre-meal)
- Effect
- Pre-meal half grapefruit produced ~1.3 kg additional weight loss in one 12-week RCT; not replicated with concurrent calorie restriction
- Best fit
- Adults using whole grapefruit pre-meal as part of a calorie-controlled diet
- Time
- Weeks (12-week trial endpoints)
Modest improvement in HDL cholesterol
- Effect
- Small HDL increases of a few mg/dL across 12-week trials
- Best fit
- Adults using grapefruit as part of a broader heart-healthy diet
- Time
- Weeks
Evidence for 3 uses
AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.
Vitamin C and fiber from a low-calorie fruit
Per USDA, half a medium pink grapefruit (~123 g) provides about 42 mg vitamin C (47% DV) and 2 g fiber for ~50 kcal. Pink and red varieties also contribute lycopene (the same red carotenoid as tomatoes) and beta-carotene. As a calorie-efficient citrus food, grapefruit is on par with oranges for vitamin C per kcal.
Bottom line: A nutritionally solid breakfast fruit if your medication list is clean. Otherwise eat oranges — they don't inhibit CYP3A4.
Modest weight loss (whole fruit pre-meal)
Supplement benefitFujioka 2006 (n=91) randomized obese adults to half a grapefruit, grapefruit juice, or placebo capsule before each meal for 12 weeks. The whole-fruit group lost ~1.6 kg vs ~0.3 kg in placebo. Silver 2011 (n=85) added caloric restriction to all arms and found no significant difference between grapefruit and water pre-meal — implying the Fujioka effect was largely calorie displacement, not a grapefruit-specific mechanism. HDL improvements favored the grapefruit groups in both trials.
Bottom line: Pre-meal grapefruit is a reasonable filler tactic on a calorie-controlled diet. It's not a metabolic shortcut, and grapefruit-extract capsules don't replicate it.
Evidence is mixed
Fujioka 2006 showed a benefit vs placebo capsule; Silver 2011 found no advantage over water when both groups were calorie-restricted. The most likely explanation is calorie displacement (eating a low-calorie fruit before a meal) — not a unique grapefruit metabolic effect.
Modest improvement in HDL cholesterol
Supplement benefitBoth grapefruit weight-loss trials (Silver 2011, Fujioka 2006) reported small HDL increases in grapefruit groups, plausibly from naringenin and other citrus flavonoids. Effect size is small (a few mg/dL) and confounded by overall dietary improvements. Whole-fruit grapefruit is not an alternative to statin therapy for cardiovascular risk reduction.
Bottom line: A small HDL lift is plausible. Don't expect it to replace evidence-based lipid management.
How it works
How to take it
What to track
Bottom line: Half a grapefruit a few mornings a week is a fine source of vitamin C and fiber — IF your medication list is clear of CYP3A4-sensitive drugs. Always check with a pharmacist for new prescriptions.
5 commercial forms
Compare the main delivery options and what they’re best suited for.
Fresh whole grapefruit (pink, red, white)
Most fiber + lycopeneHalf a medium grapefruit (~123 g) provides ~47% DV vitamin C, 2 g fiber, and pink/red varieties add lycopene and beta-carotene. The slowest-absorbed and most filling form.
Whole-fruit fiber slows fructose absorption; carotenoids best absorbed with a little dietary fat.
Fresh-squeezed or refrigerated juice
Fast vitamin C100% grapefruit juice (150 mL) retains most of the vitamin C and almost all the drug-interaction potential. Lacks the fiber of whole fruit; higher glycemic impact.
Highest furanocoumarin extraction relative to weight — strongest CYP3A4 inhibition per gram.
Shelf-stable / from-concentrate juice
Higher sugar riskOften diluted, may contain added sugars; vitamin C content slightly lower than fresh-squeezed. Read the label.
Still contains furanocoumarins; still interacts with CYP3A4 drugs.
Grapefruit-extract capsules ('fat-burner' supplements)
SkipNaringenin or grapefruit-pulp extracts marketed for weight loss. No convincing clinical trials support a metabolic mechanism. Still potentially affects CYP3A4.
Marketing claims exceed evidence; no benefit over the whole fruit.
'Grapefruit-seed extract' (GSE)
AvoidSold as a natural antimicrobial. Independent testing repeatedly finds GSE products contain synthetic preservatives (benzethonium chloride, triclosan, parabens) which provide the antimicrobial activity — the seed extract itself has none.
Mislabeling concerns documented in peer-reviewed analytical chemistry.
Safety
Know the common side effects, key cautions, and who should avoid it.
Common side effects
Serious risks
DRUG INTERACTIONS via CYP3A4 inhibition — over 85 medications affected, 43+ with potentially serious consequences (rhabdomyolysis from statins, severe hypotension from calcium channel blockers, organ-rejection or toxicity from immunosuppressants, life-threatening arrhythmias from amiodarone or dronedarone, severe sedation from buspirone or quetiapine). Effect persists 24–72 hours after a single glass. The Bailey 2013 CMAJ review is the authoritative source.
Mechanism is irreversible enzyme inhibition by furanocoumarins (bergamottin, dihydroxybergamottin). 'Separating doses' does NOT work — enzyme activity recovers only when new CYP3A4 protein is synthesized over 24–72 hours.
Seville (sour) oranges, pomelos, tangelos, and to a lesser extent limes also contain furanocoumarins and can produce the same interactions. Sweet oranges, mandarins, and lemons do NOT.
Who should avoid it
- Anyone taking simvastatin, lovastatin, or atorvastatin (statins) — risk of rhabdomyolysis. Pravastatin and rosuvastatin are safer alternatives.
- Anyone taking felodipine, nifedipine, nicardipine, nisoldipine, or verapamil (CCBs) — risk of severe hypotension and reflex tachycardia.
- Transplant patients on tacrolimus, cyclosporine, sirolimus, or everolimus — risk of toxic levels and graft injury.
- Anyone on amiodarone, dronedarone, quinidine, or some anti-anxiety meds (buspirone) or antipsychotics (quetiapine, lurasidone) — risk of QT prolongation, sedation, or toxicity.
- HIV / Hep C antivirals (saquinavir, indinavir, simeprevir) and many oral chemotherapy drugs (crizotinib, dasatinib, nilotinib, sunitinib) — toxic plasma concentrations possible.
- Anyone on a NEW prescription — confirm with the pharmacist before resuming grapefruit. New CYP3A4 substrates are approved every year.
Pregnancy & breastfeeding
Grapefruit as a food is safe in pregnancy and is a good source of vitamin C and folate. The medication-interaction concerns apply to pregnant people on prescription therapy just as they do otherwise — ask a pharmacist about any current medications.
Bottom line: As a food: very safe and nutritious. As a co-administered substance with prescription drugs: potentially life-threatening. Always confirm grapefruit safety with your pharmacist for every new medication.
Interactions
Grapefruit boosts simvastatin AUC ~3.6× and atorvastatin ~2.5× by inhibiting intestinal CYP3A4 — markedly elevated risk of myopathy and rhabdomyolysis. Use pravastatin, rosuvastatin, or fluvastatin (NOT CYP3A4 substrates) if you need a statin and want to keep grapefruit.
Felodipine AUC roughly triples with grapefruit, causing severe hypotension, reflex tachycardia, and falls in the elderly. Amlodipine and diltiazem have minimal grapefruit interaction.
Transplant patients are warned to avoid grapefruit entirely — even one glass can push these drugs into toxic range, threatening graft survival and causing nephrotoxicity.
Grapefruit increases buspirone AUC ~9-fold, producing excessive sedation and dizziness.
Grapefruit can substantially raise plasma levels, increasing risk of life-threatening QT prolongation and torsades.
Many oral oncology drugs are CYP3A4 substrates with narrow therapeutic windows; grapefruit produces toxic concentrations. Always check the prescribing information.
Boosted plasma concentrations with grapefruit can cause toxicity; check with HIV pharmacist for current regimen.
Increased plasma levels with grapefruit; risk of excessive sedation, orthostatic hypotension, QT changes.
OPPOSITE direction — grapefruit inhibits the OATP intestinal uptake transporter, REDUCING fexofenadine absorption and antihistamine effect by 30–50%. Take fexofenadine with water, not juice.
Increased plasma concentrations; ergotamine vasoconstriction can be limb-threatening at toxic levels. PDE5 inhibitors: increased risk of hypotension.
Documented interactions
Evidence-graded pair pages with sources, dosing notes, and timing guidance — a complement to the narrative section above.
Warnings (22)
+ simvastatin
criticalGrapefruit blocks the intestinal CYP3A4 enzyme that simvastatin depends on, raising simvastatin blood levels and increasing the risk of muscle damage (myopathy and rhabdomyolysis).
+ sirolimus
criticalSirolimus is a CYP3A4 and P-glycoprotein substrate with a narrow therapeutic window and high patient-to-patient variability. The FDA-approved Rapamune label states that grapefruit juice inhibits the CYP3A4-mediated metabolism of sirolimus and must not be taken with, or used to dilute, the drug, because unpredictable rises in blood levels can cause toxicity and threaten the transplanted organ.
+ red yeast rice
highGrapefruit inhibits intestinal CYP3A4, the enzyme that clears red yeast rice's active constituent monacolin K (the same molecule as the statin lovastatin). Blocking this enzyme lets more monacolin K reach the bloodstream, raising its cholesterol-enzyme-blocking activity and the associated risk of muscle-related side effects. This is a food-drug interaction driven by the grapefruit inhibitor, and because some unregulated red yeast rice products carry near-prescription statin content, the risk can be meaningful.
+ carbamazepine
highGrapefruit juice inhibits the intestinal CYP3A4 enzyme that performs first-pass metabolism of carbamazepine, allowing more of each oral dose to reach the bloodstream. A human study in epilepsy patients found grapefruit juice raised carbamazepine blood levels, which matters because carbamazepine has a narrow safety margin.
Food sources
| Food | Amount | %DV |
|---|---|---|
| Grapefruit, pink/red, raw — vitamin C | ½ medium (~123 g, 42 mg) | 47% |
| Grapefruit, white, raw — vitamin C | ½ medium (~118 g, 39 mg) | 43% |
| Grapefruit juice, fresh-squeezed | 150 mL (~58 mg vitamin C) | 64% |
| Grapefruit, pink/red — fiber | ½ medium (2 g) | 7% |
| Grapefruit, pink/red — vitamin A (carotenoids) | ½ medium (685 IU) | 14% |
| Grapefruit, pink/red — potassium | ½ medium (166 mg) | 4% |
| Grapefruit, white — folate | ½ medium (12 mcg) | 3% |
Grapefruit, pink/red, raw — vitamin C
- Amount
- ½ medium (~123 g, 42 mg)
- %DV
- 47%
Grapefruit, white, raw — vitamin C
- Amount
- ½ medium (~118 g, 39 mg)
- %DV
- 43%
Grapefruit juice, fresh-squeezed
- Amount
- 150 mL (~58 mg vitamin C)
- %DV
- 64%
Grapefruit, pink/red — fiber
- Amount
- ½ medium (2 g)
- %DV
- 7%
Grapefruit, pink/red — vitamin A (carotenoids)
- Amount
- ½ medium (685 IU)
- %DV
- 14%
Grapefruit, pink/red — potassium
- Amount
- ½ medium (166 mg)
- %DV
- 4%
Grapefruit, white — folate
- Amount
- ½ medium (12 mcg)
- %DV
- 3%
Choosing a product
What to look for on the label — and what to be skeptical of.
Look for…
Be skeptical of…
Frequently asked questions
What is Grapefruit used for?⌄
Grapefruit is used traditionally for various supportive purposes. Human evidence for specific health claims is generally limited, so it is best treated as a complementary option rather than a treatment.
Is Grapefruit safe?⌄
Grapefruit is generally well tolerated at typical doses, but quality varies between products. People who are pregnant, breastfeeding, taking prescription medications, or managing a medical condition should check with a healthcare provider first.
How long does it take to work?⌄
Effects of botanical supplements often take several weeks of consistent use, if they appear at all. Reassess after 8-12 weeks of regular use.
References by claim
Safety
Bailey et al., 2013 — CMAJ (Canadian Medical Association Journal) (2013) link
U.S. FDA Consumer Update, 2021 — FDA — Grapefruit Juice and Some Drugs Don't Mix (2021) link
Hanley et al., 2011 — PMC — Expert Opinion on Drug Metabolism & Toxicology (2011) link
Fujita & Kassai, 2014 — PMC — Drugs (2014) link
Vitamin C and fiber from a low-calorie fruit
USDA FoodData Central — Grapefruit, raw, pink and red, all areas (FDC ID 173043) (2024) link
Modest weight loss (whole fruit pre-meal)
Other references
Grapefruit on Wikidata — Wikidata link
Track Grapefruit with Pilora
Set up dose reminders, check interactions, and join the community in the Pilora iPhone app.
Coming to App StoreDisclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you’re pregnant, breastfeeding, on medications, or managing a chronic condition.