Grapefruit and your medicines: what the juice does

Nearly everything science has measured about grapefruit is about the juice, and most of it is about what the juice does to medicines. Only one study behind this page followed people eating the whole fruit, and one more used juice made up from powder. The drug finding is the solid part, and it cuts both ways. In a meta-analysis of 51 studies, grapefruit juice lowered blood levels of the blood pressure drugs aliskiren and celiprolol by about 80 to 90 percent. Most of those studies did not measure blood pressure itself, so what this means for patients is not known. In seven patients on tacrolimus, a drug that damps down the immune system, 200 ml of juice a day pushed its blood level up about 3.3-fold. That study had no control group, and the juice was given on purpose under medical monitoring. The US FDA explains the mechanism. The juice blocks CYP3A4, an enzyme in the gut that breaks some drugs down before they reach the blood, and it can also stop other drugs from being absorbed. So one glass can leave you with too much of one medicine and too little of another. For people who take no medicines at all, the evidence is thin. Across three large US cohorts, each extra 3 servings a week of whole grapefruit went with a 5 percent lower risk of type 2 diabetes. That comes from watching what people ate, so it cannot show the fruit caused the difference.

The numbers, per 100 g

How much is actually in it

• NIH lists grapefruit juice among foods with large amounts of vitamin C, and notes that many of the best food sources of the vitamin are usually eaten raw. — General population Evidence E source
  Qualitative

What your body absorbs

• One 300 ml glass of grapefruit juice lowered blood exposure to the beta blocker talinolol to 56% of the level seen with water in 24 healthy adults. — 24 healthy white volunteers, 50 mg talinolol with water, one 300 ml glass, or after 6 days of 900 ml/day juice (n = 24) Evidence C source
  AUC and Cmax fell to 56-57% of water; repeated intake cut them 44-65%
• In 11 volunteers drinking juice made from grapefruit powder, serum vitamin C rose 12% and naringenin 28%, with no difference between freeze-dried and spray-dried powder. — 11 volunteers, two reconstituted grapefruit juices from freeze-dried or spray-dried powder (n = 11) Evidence C source
  Serum vitamin C +12%, naringenin +28%, antioxidant capacity +26%; 1.529 mg vitamin C/L serum per 100 mg ingested

What it does to your health

• Adding 250 ml grapefruit juice to a beetroot juice shot lowered systolic blood pressure by a further 3.3 mmHg at 5 hours in 11 healthy volunteers. — 11 healthy volunteers, 70 ml nitrate-rich beetroot juice with 250 ml grapefruit juice or water, 7-hour visits (n = 11) Evidence B source
  Peak systolic difference -3.3 mmHg (95% CI -6.43 to -0.15) at 5 h; plasma nitrite was lower, against the hypothesis
• Across three US cohorts, each 3 servings a week of whole grapefruit was linked to a 5% lower risk of type 2 diabetes (HR 0.95), while fruit juice was linked to 8% higher risk. — 187,382 US nurses and health professionals followed up to 24 years, 12,198 new diabetes cases (n = 187382) Evidence C source
  HR 0.95 (0.91 to 0.99) per 3 servings/week grapefruit; HR 1.08 (1.05 to 1.11) for fruit juice

Safety, limits and interactions

• In a meta-analysis of 51 studies, grapefruit juice cut blood exposure (AUC and Cmax) of the blood pressure drugs aliskiren and celiprolol by about 80-90%. — Healthy volunteers and patients in 51 mostly small open-label crossover studies (n = 51 studies) Evidence A source
  AUC and Cmax down about 80-90% for aliskiren and celiprolol; calcium channel blockers changed to variable degrees
• Three days of 250 ml grapefruit juice raised dapoxetine AUC by 60% and peak level by 80%, and midazolam AUC by 75%, in 12 healthy adults. — 12 healthy men, 250 ml undiluted grapefruit juice daily for 3 days before a single drug dose (n = 12) Evidence C source
  Dapoxetine AUC +60%, Cmax +80%, half-life +43%; midazolam AUC +75%
• Taking the lung fibrosis drug pirfenidone with grapefruit juice roughly halved its peak blood level (5.8 vs 10.9 mg/L) in 12 healthy men, similar to taking it with food. — 12 healthy Chinese men, single 0.4 g pirfenidone dose fasted, fed, or with grapefruit juice, 7-day washout (n = 12) Evidence B source
  Cmax 5.82 vs 10.90 mg/L; AUC0-12h change not statistically significant
• The US FDA warns that grapefruit juice can block intestinal CYP3A4 so more of some drugs enters the blood, and can also make less of drugs such as fexofenadine get absorbed. — People taking prescription or OTC drugs Evidence E source
  Direction depends on the drug
• A review of 120 studies on macrolide and tetracycline antibiotics found grapefruit juice had variable effects on their absorption, with evidence quality rated low. — Adults taking oral macrolides or tetracyclines in 120 pharmacokinetic studies (n = 120 studies) Evidence A source
  Variable direction of effect on absorption for grapefruit juice; evidence quality rated low

What people believe that the data does not support

• An EU application to say grapefruit acts as a purifying agent with antioxidant protection was rejected, status Non-authorised. — EU health claim applicants Evidence E source
  Claim status Non-authorised
• The EU did not authorise the claim that grapefruit flavonoids contribute to microbial balance in body organs and tissues. — EU health claim applicants Evidence E source
  Claim status Non-authorised
• In a survey of 103 adults with type 2 diabetes, knowledge of drug interactions with grapefruit juice was among the largest gaps. — 103 adults with type 2 diabetes (n = 103) Evidence C source
  Substantial knowledge gaps; dietary consultation linked to higher knowledge (OR 2.31)

Who this works differently for

• In 7 patients with connective tissue disease, 200 ml of grapefruit juice a day raised tacrolimus trough levels from 4.3 to 13.8 ng/mL, about 3.3-fold. — 7 Japanese patients on at least 3 mg/day tacrolimus with low blood levels, given the juice on purpose under medical monitoring, no control group (n = 7) Evidence C source
  Trough 4.3 to 13.8 ng/mL, mean 3.3-fold, in an uncontrolled study of deliberate use under monitoring; some levels fluctuated without clear reason
• In 2,832 Swedish twins, liking for bitter foods such as grapefruit showed the strongest genetic influence among taste preferences, within a heritability range of 21-61%. — 2,832 Swedish twins, mean age 24 (n = 2832) Evidence C source
  Taste preference heritability 21-61%, highest for bitter foods
• A systematic review of 23 studies on epilepsy drugs and food reports that grapefruit juice raises carbamazepine levels, while rating all included evidence as low level. — People with epilepsy taking antiseizure medicines (n = 23 studies) Evidence C source
  Carbamazepine concentrations increased; size not given in abstract
• A kidney transplant patient's tacrolimus level rose sixfold to 30 µg/L after about 1 litre of blood orange juice followed by 250 ml of grapefruit juice. — One 33-year-old male kidney transplant recipient (n = 1) Evidence C source
  Tacrolimus 4.5 to 30 µg/L overnight; drug paused, patient stabilised

What is still unknown

• A 2026 genetic study of 19,653 US adults found only a suggestive gene signal for grapefruit intake and a possible obesity link in women, which the authors call preliminary. — 19,653 European-ancestry adults in NHS and HPFS cohorts (n = 19653) Evidence C source
  Lead SNP below genome-wide significance; CC genotype linked to modestly higher obesity risk in women only

The bottom line

If you take a regular medicine, ask your pharmacist whether grapefruit affects it before you make the juice a habit. The answer depends on the drug, and it is often a surprise. A single 300 ml glass cut blood levels of the beta blocker talinolol to 56 percent of what water gave. With the lung fibrosis drug pirfenidone, juice roughly halved the peak level, about the same as taking it with a meal. Three days of 250 ml raised the level of dapoxetine by 60 percent. For people with epilepsy, a review reports that the juice raises carbamazepine, while rating every study it included as low level evidence. A review of 120 studies on common antibiotics found the effect went in different directions and rated that evidence low as well. For the blood pressure drugs, the meta-analysis authors say most studies never checked blood pressure itself, so how much the drop in drug level matters to a patient is still open. Transplant patients have the least room for error. One man on tacrolimus saw his level jump sixfold overnight, to 30 µg/L, after about a litre of blood orange juice followed by 250 ml of grapefruit juice. It is easy to miss. In a survey of 103 adults with type 2 diabetes, grapefruit interactions were among the biggest gaps in what people knew, and those who had talked to a dietitian knew more. Every interaction study here used juice. None tested the whole fruit, so we cannot tell you whether half a grapefruit at breakfast acts the same way. Our cards include no study of the whole fruit, so treat the fruit with the same caution. The rest is small. NIH lists grapefruit juice among the foods with large amounts of vitamin C. In 11 volunteers drinking juice made from powder, blood vitamin C rose 12 percent. Adding 250 ml of grapefruit juice to a beetroot juice shot lowered systolic blood pressure by a further 3.3 mmHg at five hours in 11 people. The marker that was supposed to explain it moved the wrong way, so that result waits for a bigger trial. Two health claims filed for grapefruit in the EU were not authorised, one built on its antioxidants and one on its flavonoids and the microbes in the body. Whether you like the bitterness is partly inherited: among 2,832 Swedish twins, bitter foods such as grapefruit showed the strongest genetic pull of any taste. A gene study that hinted at a link between grapefruit and obesity in women is called preliminary by its own authors. What our cards do not cover at all: pregnancy, children, how much fruit it takes to affect a drug, and what the tinned sections in our table do compared with fresh fruit.

Sources

1. grf-18 · fact sheet
   Orange juice, grapefruit juice, and tomato juice also contain large amounts of vitamin C, and vitamin C is added to some breakfast cereals. ... Fortunately, many of the best food sources of vitamin C, such as fruits and vegetables, are usually consumed raw.
   NIH Office of Dietary Supplements, Vitamin C Fact Sheet for Health Professionals · checked 2026-09-23
2. grf-03 · clinical trial
   A single glass of grapefruit juice decreased the talinolol area under the serum concentration-time curve (AUC), peak serum drug concentration (Cmax), and urinary excretion values to 56% (P < .001), 57% (P < .001), and 56% (P < .001), respectively, of those with water. Repeated ingestion of grapefruit juice had a similar effect (44% to 65% reduction; P < .01).
   Clin Pharmacol Ther, 2005 · checked 2026-09-23
3. grf-08 · clinical trial
   No significant differences (p > 0.05) neither by juice nor by participant were observed in any case. The mean relative increase of VC, NAG and the radical scavenging ability (RSA) in blood serum due to grapefruit juices intake was 12%, 28% and 26%, respectively. ... The mean bioavailability of VC was quantified as 1.529 ± 0.002 mg VC/L serum per 100 mg of VC ingested.
   Molecules, 2023 · checked 2026-09-23
4. grf-05 · randomised crossover trial
   The addition of grapefruit juice to active beetroot juice lowered systolic BP (SBP) ... Peak mean differences in SBP and PP were seen at T = 5 hours: -3.3 mmHg (95% confidence interval [CI] -6.43 to -0.15)
   Br J Clin Pharmacol, 2021 · checked 2026-09-23
5. grf-07 · cohort
   With mutual adjustment of individual fruits, the pooled hazard ratios of type 2 diabetes for every three servings/week were 0.74 (0.66 to 0.83) for blueberries ... 0.95 (0.91 to 0.99) for grapefruit ... The pooled hazard ratio for the same increment in fruit juice consumption was 1.08 (1.05 to 1.11).
   BMJ, 2013 · checked 2026-09-23
6. grf-01 · meta-analysis
   Grapefruit juice (GFJ), an inhibitor of organic-anion-transporting polypeptide (OATP) transporters and cytochrome P450 (CYP) 3A4, significantly decreased the AUC and Cmax of aliskiren and celiprolol by approximately 80-90 %. ... Hemodynamic effects were not assessed in most studies; thus, the clinical significance of these interactions remains uncertain and should be further investigated.
   Complement Ther Med, 2025 · checked 2026-09-23
7. grf-02 · crossover trial
   Compared to pretreatment with water, GFJ increased the area under the plasma concentration-time curve from time zero to infinity (AUC0-∞) and peak plasma concentration (C max) of dapoxetine by 60 and 80 %, respectively, and prolonged its elimination half-life (t 1/2) by 43 %. Similar effects of GFJ on the pharmacokinetics of midazolam were observed with a significant increase in AUC0-∞ (75 %), C max (40 %), and t 1/2 (92 %).
   Eur J Drug Metab Pharmacokinet, 2017 · checked 2026-09-23
8. grf-04 · randomised crossover trial
   Similar effects on Cmax (5.8 2 ± 1.23 versus 10.9 0 ± 2.94 mg·L(- 1)) ... Co-administration of pirfenidone with grapefruit juice resulted in modestly reduced overall oral absorption and significantly reduced peak concentrations compared to fasting, which was similar to effect of food ingestion.
   Xenobiotica, 2016 · checked 2026-09-23
9. grf-11 · agency guidance
   Grapefruit juice can block the action of intestinal CYP3A4, so instead of being metabolized, more of the drug enters the blood and stays in the body longer. The result: too much drug in your body.
   US Food and Drug Administration, Grapefruit Juice and Some Drugs Don't Mix, updated 2021 · checked 2026-09-23
10. grf-15 · meta-analysis
    We included 120 studies from 97 reports. ... Milk and grapefruit juice showed variable impacts on absorption. ... The quality of evidence was rated low due to outdated studies, methodological diversity and unequal data availability.
    J Antimicrob Chemother, 2024 · checked 2026-09-23
11. grf-09 · regulatory register
    POL-HC-7224 Grapefruit (Citrus paradisi Mact. = C. decumana L., C. grandis Osbeck ; Citrus maxima) May help the detoxification process. Possesses antioxidant activity. Can be considered as a detoxifying / purifying agent, due to its antioxidant properties. Provides antioxidant protection. Non-authorised
    EU Register on nutrition and health claims, claim POL-HC-7224, snapshot 2026-09-21 · checked 2026-09-23
12. grf-10 · regulatory register
    POL-HC-6938 Citrus paradise (Common Name : Grapefruit) Flavonoids contained within the Grapefruit contribute to the microbial balance in the body organs and tissues Non-authorised
    EU Register on nutrition and health claims, claim POL-HC-6938, snapshot 2026-09-21 · checked 2026-09-23
13. grf-17 · cross-sectional
    Substantial gaps in DFI knowledge were identified, particularly regarding interactions involving dietary fiber, dairy products, grapefruit juice, and nutrient deficiencies associated with long-term pharmacotherapy.
    Nutrients, 2026 · checked 2026-09-23
14. grf-06 · uncontrolled clinical study
    GFJ increased the TAC level from 4.3±2.4 ng/mL to 13.8±6.9 ng/mL (average increase: 3.3-fold).
    Intern Med, 2016 · checked 2026-09-23
15. grf-12 · twin study
    Taste preferences also showed substantial genetic contributions (21%-61%), with the strongest effects observed for bitter foods (e.g., black coffee, grapefruit), followed by sweet foods (e.g., jam/marmalade).
    Am J Clin Nutr, 2026 · checked 2026-09-23
16. grf-14 · systematic review
    All studies provided low level of evidence. ... grapefruit juice increases carbamazepine concentrations
    Epilepsia Open, 2024 · checked 2026-09-23
17. grf-16 · case report
    The following morning, his tacrolimus concentration had risen sharply sixfold to 30 µg/L, far above the increase typically associated with grapefruit juice alone.
    J Med Case Rep, 2026 · checked 2026-09-23
18. grf-13 · cohort
    In age- and multivariate-adjusted models, the CC genotype was associated with a modestly increased risk of incident obesity in females, but not in males. ... However, given the lack of genome-wide significance and independent replication, these findings should be considered preliminary and exploratory.
    Nutrients, 2026 · checked 2026-09-23