Grapefruit: The Phantom Menace

Vitamins or harm?

Drink­ing a glass of grape­fruit juice has al­ways been the health­i­est way to start your day. There is no doubt that grape­fruits are rich in vi­ta­mins and oth­er nu­tri­ents. But can this re­mark­able fruit do more harm than good?

[Deposit Photos]

A hid­den dan­ger

Over 20 years ago, doc­tors dis­cov­ered that only one glass of grape­fruit juice can triple the con­cen­tra­tion of cer­tain drugs – can­cer, heart, seda­tive, choles­terol and painkilling medica­ments. Ini­tial­ly, 17 such drugs were iden­ti­fied, but their num­ber has since in­creased to 43, ac­cord­ing to a re­port in the Cana­di­an Med­i­cal Jour­nal¹. The side ef­fects of con­sum­ing grape­fruit may in­clude low blood pres­sure, the col­lapse of the im­mune sys­tem, etc.

Why does this hap­pen?

The rea­son why grape­fruits make drugs more po­tent lies in chem­i­cals called fu­ra­nocoumarins. These com­pounds, which are pro­duced by plants to de­fend them­selves against preda­tors, in­ter­fere with en­zymes in our in­testines. These en­zymes are in­volved in the me­tab­o­lism of some drugs and con­trol their amount in the blood­stream. How­ev­er, if fu­ra­nocoumarins are present in the in­testines, they block the en­zymes. This leads to the risk of an over­dose.

Angelicin – a typical furanocoumarin [Wikimedia]

Which drugs are dan­ger­ous?

Creative Commons by Erich Ferdinand is licensed under CC BY 2.0 [Flickr]

The range of drugs af­fect­ed by grape­fruit is very ex­ten­sive. The most af­fect­ed group of drugs is statins – tak­en all over the world to low­er choles­terol. The an­tibi­ot­ic ery­thromycin is also dan­ger­ous if you have eat­en a grape­fruit. Oth­er haz­ardous drugs are seda­tives, drugs for kid­ney, skin and blood can­cer, blood-thin­ning med­i­ca­tion and painkillers.

What are the side ef­fects?

The side ef­fects of mix­ing drugs with grape­fruits vary from drug to drug. The con­se­quences are un­ex­pect­ed. There may be an al­ler­gic re­ac­tion, or in some cas­es ir­reg­u­lar heart­beats, fol­lowed by sud­den death. Anti-can­cer drugs are the most dan­ger­ous to com­bine with grape­fruit - they cause the col­lapse of the im­mune sys­tem. Blood-thin­ning and choles­terol drugs may cause stom­ach bleed­ing, kid­ney fail­ure, swelling, vom­it­ing and di­ar­rhea.

[Deposit Photos]

Are there oth­er fruits with the op­po­site ef­fect?

Cu­ri­ous­ly enough, or­ange and ap­ple juice may make some can­cer, heart and blood pres­sure drugs less po­tent. The op­po­site ef­fect was also caused by naringin (a chem­i­cal which makes cit­rus fruits bit­ter). It pre­vents the drugs from mov­ing into the blood­stream.²

What should we do to avoid risks?

[Deposit Photos]

Grape­fruits are very healthy and nu­tri­tious. We should eat them reg­u­lar­ly, as they are a great source of mi­croele­ments and rare or­gan­ic acids. How­ev­er, it is very im­por­tant to re­frain from eat­ing them while tak­ing some drugs. The ma­jor­i­ty of these med­i­ca­tions are pre­scrip­tion-only, and the doc­tor should in­form pa­tients if there are prob­lems with grape­fruit. It is es­sen­tial not to ig­nore these warn­ings.

To find out more about this is­sue, see this video from The Uni­ver­si­ty of West­ern On­tario:

P.S. This is a pop­u­lar sci­ence ar­ti­cle. It should not be treat­ed as med­i­cal ad­vice or a guide to ac­tion.


  • ¹Grape­fruit juice: po­ten­tial drug in­ter­ac­tions. James Maska­lyk, CMAJ Au­gust 6, 2002 vol. 167 no. 3;

  • ²Fruit juices in­hib­it or­gan­ic an­ion trans­port­ing polypep­tide–me­di­at­ed drug up­take to de­crease the oral avail­abil­i­ty of fex­ofe­na­dine. David G. Bai­ley PhD et. al., Clin­i­cal Phar­ma­col­o­gy & Ther­a­peu­tics, Vol­ume 71, Is­sue 1, pages 11–20, Jan­u­ary 2002*