There are 44 prescription drugs on the market today that should never be combined with grapefruit. That's because the sour fruit (and some other, closely related, kinds of citrus) contain chemical compounds called furanocoumarins that prevent your body from metabolizing certain prescription drugs. Essentially, the grapefruit creates an artificial overdose where one tablet packs the power (and side effects) of 20. The CBC has a full list of the drugs, which includes cancer drugs, cholesterol-lowering drugs, and drugs to treat problems of the urinary tract. Wikipedia has more about why this interaction happens.

  • http://www.facebook.com/profile.php?id=1515015318 Missy Pants

    Also MDMA. 
    Not that I know that from personal experience or anything… just, uh, a friend told me… yeah.

    • dragonfrog

      And psilocybin.

  • SamSam

    My doctor’s office has giant posters.

    DO YOU EAT GRAPEFRUIT???!?!? BE SURE TO TELL YOUR DOCTOR!!!!!!!1

    translated into 15 languages.

  • getawaysticks

    Thank you for posting this. I am on one of those drugs and drink grapefruit juice sometimes on the weekends – and had no idea.

  • Jason Sutor

    Its not all grapefruit equally though. Some cultivars were found to not have the bad compounds in them. Wish I had the link, my fruit nerd friends were deep into the research since they grew collectively 30+ types of grapefruit and wanted to know which were safe with their medications.

    • billstewart

      Radio the other day mentioned that some university has been breeding grapefruits that are safe with statins and other drugs.

      Meanwhile, noticing quinine there – no grapefruit&tonic?

      • IronEdithKidd

        I was thinking the same thing, only limeade, tonic and gin. Gin over quinine?

      • SamSam

        Barely any quinine in tonic anymore, even the fanciest ones. Certainly not enough to be considered “medicinal.”

    • Jason Sutor

       http://www.scientificamerican.com/podcast/episode.cfm?id=hybrid-grapefruit-busts-drug-intera-11-11-08
      This article has the link to the publication

  • Frank W

    So some 44 prescription drugs could pull the same punch at 5 % of the dosage, and toxicity, if they were rolled into a pill with those furanocoumarins? Is there research into that?

    • toasterslie

      There actually is, but most of the cost of these drugs has little to do with the cost of the raw materials. Businesses don’t want to spend $100,000+ to get approval on a new drug formulation just to add grapefruit to it.

      • http://billmcgonigle.com bill_mcgonigle

        Yeah, but that only applies to people living under regimes with these sorts of rules.  Charities that are trying to get medication in third-world countries that don’t have these problems and where the cost of drugs is a significant problem could probably use this technique.  As a bonus, they might be able to pay people to grow the grapefruits and others to refine them.

  • tomservojr

    Grapefruit also interferes with a lot of anti-seizure medications, but those aren’t covered in the article. Worth looking into if you’re taking one (or know someone who is).

    • http://weirdly.net Jacob Ewing

       Indeed.  It was one of the things I rather disliked about carbamazepine (a.k.a. Tegretol) when I was taking it.

      Although I’ll admit I was more bothered by fact that you’re not supposed to drink alcohol while taking it.

      • http://daruiburns.tumblr.com/ Dlo Burns

        No greyhounds then?

  • toasterslie

    Also take note that grapefruit is used as a flavoring in some foods, especially sodas. We had a patient on Lipitor showing signs of rhabdomyolysis. Turns out he was drinking several Frescas each day and didn’t see what that had to do with those grapefruit warning labels we put on every bottle.

    • http://daruiburns.tumblr.com/ Dlo Burns

      Squirt is flavored with it too.

    • http://www.facebook.com/profile.php?id=13001904 Jeremy Sweeney

      Oh my god. Rhabdo – the #2 most common differential on House. 

  • gadgetphile

    Back in August of 2008 there was also a story out about orange juice not mixing well with prescription drugs either. Is this because of mixing grapefruit with orange juice, or is it just a citrus thing?

    I haven’t seen the warnings- are they specifically pointing out grapefruit or other things too (like other citrus)?

  • http://www.aarongilliland.com/ Aaron Gilliland

    The Coles Notes version:  when your doctor prescribes a drug, the dosage is based on certain assumptions about your body.  Drugs can be broken down and changed into different compounds as they move through the body.  Enzymes can make the drug’s molecules inert or less effective, some of the drug will move through parts of the body where it has no effect, some of it gets filtered by the kidneys, etc.  The goal is to have enough of the drug, at the right place, for a long enough duration to be effective.  So to meet that goal, you have to know how the drug is broken down (the different enzymes, excretion, etc.), how fast it breaks down, what’s the minimum dose that is effective in the treatment population, etc. etc. etc.   Knowing all of that, and making the assumption that the patient’s body will have the same rates of metabolism, the doctor makes the prescription.

    It’s like trying to make enough cookies to fill a delivery truck, but there’s a wild pack of Cookie Monsters roaming the bakery and NOM NOM NOMing.  In order to fill the truck, you’ll have to make a full truckload PLUS enough cookies to keep the monsters busy.

    The grapefruit problem, as it shall be known ;), is about enzyme Cytochrome P450 3A4.  The enzyme is supposed to go NOM NOM NOM like a good Cookie Monster, but the chemical in the grapefruit stuffs a giant marshmallow in the monster’s mouth, so he can’t NOM.

    The result is that you make way too many cookies and you have to eat all the extras and you become a Hutt and the world explodes.  Or, uh, more of the drug acts on your system than was expected, and you become unwell, and the world explodes.

    That was supposed to be the quick version…

  • http://goodsharer.com/ Aloisius

    Who eats grapefruit? Seriously, it has to be the worst of all fruits. I’m shocked they even sell it in the market. Some Israeli parents serve grapefruit for breakfast every morning because its bitter taste evokes the suffering of the Jews.

    The only time it I can stomach it is if you juice it, add a *ton* of sugar and some bubbles. But then I’m just drinking sugar water with a little grapefruit flavoring.

    • http://daruiburns.tumblr.com/ Dlo Burns

      Some breeds are better than others, and some people just really f’n love tart things.

    • http://billmcgonigle.com bill_mcgonigle

      First, quit sugar.  Grapefruits are naturally sweet, but if you’re a sugar junkie your sweet receptors will be deadened.   They’ll come back in a couple months.

      For a shortcut, drop a Miracle Fruit Tablet and then try eating it – it’s like a totally different fruit – I actually find them too sweet without the sour flavor masking it!

    • SamSam

      Pah, I pity the unfortunate souls who have never developed an adult appreciation for bitter foods.

      And don’t tell me you’re a super-taster. I’ve done the tests and can taste all the bitter compounds, and still love grapefruit.

    • Antinous / Moderator

      Are you on crack? Grapefruit is delicious. Orange juice is nauseatingly sweet.

      • http://goodsharer.com/ Aloisius

         I am hardly the only one. I give you, Google…

    • http://twitter.com/MileHiSandy Sandy

      I eat 1/2 graperfruit every morning.But I also like Sour Patch Kids, those sour cherry candies, Gr.Fruit juice, lemonade, limeade, etc.

  • http://daruiburns.tumblr.com/ Dlo Burns

    My mom takes transplant related drugs that can be negated by grapefruit, which is sad since she’s the only one in the family who ever really liked them.

    /edit: also grapefruit are call that because they grow in clusters on the tree so stop being a smart ass

    • http://freddiefreelance.blogspot.com Freddie Freelance

      I also love grapefruits. And your Mom, but not in that creepy way.

  • http://twitter.com/Adel_wolf Adelwolf

    Knowing this would have been nice when I was on buspirone.  Not that I’m a big fan of grapefruit, but as toasterslie and Dlo Burns mentioned, some tasty items have it as flavoring. I don’t remember if I ever had any Fresca during that time, but I ended up okay.

  • Jillian Galloway

    Can we all say “Grapefruit Prohibition”? After all, the alcohol prohibition was a deadly failure and the marijuana prohibition is a deadly failure, so let’s (for the sake of the children) have a grapefruit prohibition. All we have to do is demonize the plant, arrest hundreds of thousands of people every year for possessing it and create a massive black market for it – then we’ll have achieved the exact same results that the alcohol and marijuana prohibitions have. 

  • http://www.facebook.com/roadjunkie Road Junkie

    So drugs companies can give us a lower dosage if they mix grapefruit juice in it? I’m all for that.

  • http://www.xeni.net/ Xeni Jardin

    Yep, familiar with this. I was told to stop eating grapefruit when my chemo began because it can reduce efficacy of drug. And now that I’m on hormone therapy for cancer, it’s newly verboten. Used to love it!

    • Luther Blissett

      Xeni, I would have posted this just as a random addition somewhere in the thread, but it might be important to you: don’t drink to much Earl Grey (and other stuff with Bergamott in it). The same mechanism as in Grapefruit. See Wikipedia, for a start.

      BTW, since maybe spring will start somewhere on the northern hemisphere: allergics are affected as well. Cetirizine and allied antihistaminics may be metabolized differently when you take these plant metabolites. Don’t go crazy about it, but be aware.

      • Antinous / Moderator

        Is that why Irumodic Syndrome was incurable?

        • http://www.aarongilliland.com/ Aaron Gilliland

          You magnificent bastard.

  • Aaron Harmon

    Good thing that grapefruit tastes like bitter feet. I might have hurt myself.

  • http://www.facebook.com/agent139 Jamie Lee

    It also increases the duration though not general potency of opiates, which can be useful when you’re trying to increase the efficacy of your prescription meds during a hard month. It’s definitely good to be aware of though. 

  • http://www.facebook.com/profile.php?id=13001904 Jeremy Sweeney

    This is why I used to drink tons of grapefruit juice. Super fun when you’re on SSRIs and SNRIs.

  • http://www.tavie.com Tavie

    Geez. My (elderly) Dad is on Lipitor, among other drugs – Lipitor’s definitely on the list, though – and eats at LEAST a grapefruit every day. He’s crazy about grapefruit.

    Going to ask him to talk to his doctor about this…

  • http://mcdevzone.com/ mike3k

    I never liked grapefruit.

  • Bill Mungai

    Have 10 gallons of grapefruit wine fermenting away. I wonder if the fermentation process makes any difference?

  • jroycenewman

    Guys. Ask your pharmacist. They spent their entire college education learning about just these issues and they will explain what the risks of grapefruit will be. If yours won’t make some general statements about “very dangerous” vs. “probably fine, just look out for symptom X”, then get a new pharmacist. 

  • http://twitter.com/ErnestValdemar Ernest Valdemar

    I am actually drinking Fresca right this very moment, which is odd because I don’t typically drink Fresca. While I enjoy the occasional Fresca, I’m quite surprised that any active components of natural grapefruit  can be found in this tasty stew of acids, Aspartame, “natural & artificial flavors,” vegetable gums, preservatives, and, believe it or not, “ester of rosin” and “acacia.” Fresca is made of trees!

    • http://daruiburns.tumblr.com/ Dlo Burns

      Ester of rosin is used to make citrus oil mix with sugar water.

  • Promethean Sky

    One of my medications has this interacting, good thing I’ve always despised grapefruit. I find it odd that so many people are unaware of this. When I get my medications filled, there are brightly colored stickers on the pill bottles with warnings.