How Grapefruit Affects Prescription Drugs

Image Credit: Liz West / Flickr. This image has been modified.

How Grapefruit Affects Prescription Drugs

Does grapefruit in particular help people lose weight?

If someone eats half of a grapefruit three times a day before each meal for a couple months, they may lose about two pounds — but that’s no more than if they ate three apples or pears a day. In one study, the grapefruit eaters not only saw their weight go down, but their waist got slimmer, and their body fat melted away. If, however, we repeat the experiment and instead ask people to drink a half cup of water before each meal, we get the same result. So this belief that grapefruit has some special fat-burning quality appears to be just a long-held myth.

The researchers reported that grapefruit consumers had a drop in weight, a significant drop in cholesterol, and a significant drop in blood pressure. They concluded that consumption of grapefruit daily for six weeks does not significantly decrease body weight, cholesterol, or blood pressure, though. That made me do a little double take, but again, it’s because the grapefruit didn’t do any better than placebo.

Other studies have found a legitimate cholesterol-lowering benefit of grapefruit, and even a little dip in triglycerides, especially eating red as opposed to white . For example, one study showed a decrease in cholesterol, but only from one life-threatening cholesterol level to another life-threatening cholesterol level. To prevent heart disease, we really have to get down to a total cholesterol of around 150, which is the average cholesterol of those eating diets composed exclusively of plant foods, not just grapefruits (See, for example, One in a Thousand: Ending the Heart Disease Epidemic).

Even though grapefruits alone don’t do much, the researchers suggest that people might be more likely to stick with them than cholesterol lowering drugs, noting that most people with heart disease stop taking their statin drugs within a couple years because of the adverse side effects (see Statin Muscle Toxicity). While grapefruits alone don’t have any side effects, ironically, combining grapefruits and drugs can make drug side effects even worse.

If we eat lots of fruits and vegetables, we hopefully won’t need a lot of drugs (Say No to Drugs by Saying Yes to More Plants), but certain phytochemicals in plants can affect the metabolism of drugs in the body. Grapefruit is the poster child, described as a “pharmacologist’s nightmare.” Natural phytochemicals in grapefruit suppress the enzymes that help clear more than half of commonly prescribed drugs, and less drug clearance means higher drug levels in the body. This may actually be good if we want a better caffeine buzz from our morning coffee, or our doctors want to help us save thousands of dollars by boosting the effects of expensive drugs instead of just peeing them away.

But higher drug levels may mean higher risk of side effects. Women taking the Pill are normally at a higher risk of blood clots, but even more so, perhaps, if they have been consuming grapefruit. Taking the Pill with grapefruit juice may increase blood drug concentrations by 137 percent.

If suppressing our drug clearance enzymes with grapefruit juice elevates levels of ingested estrogen, what might it be doing to our own estrogen levels? A study associating grapefruit consumption with breast cancer freaked out the medical community, but subsequent studies on even larger groups of women found no evidence of a link. The Harvard Nurses’ Study even found a decreased risk of the scariest breast cancer type, so it doesn’t look like we have to worry about grapefruit affecting our natural chemistry.

For those prescribed unnatural chemistries, it may be a good idea to discontinue grapefruit consumption for 72 hours before use of a drug that may interact with it. If you don’t want to give up your grapefruit, you can ask your doctor about switching from a grapefruit-affected drug like Lipitor to one of the citrus-proof alternatives (the replacement drug chart can be seen in my video, Tell Your Doctor If You Eat Grapefruit).

Other videos on citrus include:

And another video on the risks associated with taking estrogens: Plant-Based Bioidentical Hormones.

Can’t eat grapefruit without sprinkling sugar on top? Try erythritol instead to avoid so many empty calories: Erythritol May Be a Sweet Antioxidant.

-Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my videos for free by clicking here and watch my full 2012 – 2015 presentations Uprooting the Leading Causes of Death, More than an Apple a Day, From Table to Able, and Food as Medicine.


Michael Greger M.D., FACLM

Michael Greger, M.D. FACLM, is a physician, New York Times bestselling author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous "meat defamation" trial.

19 responses to “How Grapefruit Affects Prescription Drugs

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  1. Are there any other fruits that have this reduced drug clearance effect? Could this be the reason why so many people who go raw vegan end up developing intolerance to caffeine – in even the smallest amounts?

  2. Please consider the fact that the majority of the desired phytochemical compounds in any discussion of plant-based healing and body-tweeking, are typically found in the skin, the layer just under the skin, and the seeds of (for example) citrus, peppers, berries, pomegranates, apples, apricots/peaches, etc. This means there HAS to be a difference in bio-availability (and cost-effectiveness!) of whole food machine preparation made possible with a Vita-Mixer, Bullet, or high-powered blender type machine. This needs to be pointed out and noticed by everyone no matter which stage you are committed to – ;the Cancer Prevention, Cancer Suppression, or the Cancer Cell Apoptosis Diet. For someone like me, in Month 9 of my “Alternative Cancer Treatment” (Protocol #4) of a what is looking like a full calendar year of successfully treating multiple cancers in my body. these details matter due to cost alone. I have accomplished this on an extremely small monthly subsistence income (Social Security), and had zero room for error, waste, or lost opportunity for maximizing benefits whereever feasible. After 4 months of no/extremely low carbs (NO grains or sugars from any source), I have been able to add in a daily Medicine Dessert Salad comprised of: 1-2 Pink Grapefruit cut up, 2-4 thumbs grated/sliced fresh ginger root, 1/2 cup packed minced Cilantro. This anti-parasite, heavy metal detox, cancer cell apoptosis-inducing plateful of deliciousness is only possible if you are not taking any pharmaceuticals, because whatever causes grapefruit to interact with drug clearing in our body is magnified many times when you turn these 3 phytochemicals into a synergistic medicine dish. Oh, and don’t forget to knife off just the barest of the outer flesh, leaving the most “white” possible on the grapefruit – this is giving yourself the highest amounts of hesperin and the other medicine components we want more of everyday. The other method is to take the partially peeled citrus fruit and throw into a blender type machine which will trichurate the bioflavinoids, rutin, hesperin, etc., found in the edible skin and seeds….this is cost-effective, whole food / plant-based alternative chemotherapy.

      1. The #1 required food energy source for cancer cells to survive, multiply and grow is sugar; it does not matter the source – fructose, starch, honey, processed HFCS. Sugar feeds cancer cells. This FACT is agreed upon by conventional oncologists as well as alternative oncologists. The standard anti-cancer diet is removing their fuel source (sugar) and when the cancer cells are down, you hit them with the correct known cancer cell killing plant medicines and strategic supplements known to support the action of these cancer cell destroying herbs, roots, mushrooms, barks, flowers (my daily regimen involves up to 14 different ones). Cancer cells can also derive fuel from high-protein animal foods, but it takes much more effort and time for them to convert from this food source; nevertheless, I did remove all animal also. Gluten is involved also in terms of efficiency of your plant medicine diet, even is you are not officially gluten-intolerant. Alkalinizing your body (recognized by outcome not ingoing – lemons for example are acid but produce alkaline reaction) will happen automatically if you have switched to only consuming the correct foods (mostly certain vegetables), are sufficiently hydrated, have sufficient volume (bulk, fiber) going through your system, are resupplying your gut with the broadest spectrum probiotics, and at some point (mine was Protocol #3), you need to address the removal of heavy metals and parasites – this phase of my treatment was/is the most interesting and resulted in the most QOL improvements. The NO carb first few months led to the ability to introduce small amounts of carbs without symptoms returning – once / month I tested with a homemade dessert to prove to myself what I was reading. Cancer cells LOVE sugar and the sensation is similar to relapsing when trying to withdraw from a drug addiction. In fact, many studies show the exact center of the brain is activated in sugar addiction as with drug and alcohol addiction. I will be watching my carbohydrate consumption for the rest of my life and use the sugar craving as my gauge for whether or not I am feeding cancer cells too much – it is now known we are all born with damaged DNA/cancer capable cells in our bodies; they will morph into cancerous cells if the conditions are correct – exposures to carcinogens, malnutritiion, etc. I intend to starve the cancer cells in my body for the rest of my life by not giving them their favorite food.

        1. Has this method been studied, tested by scientists/researchers? Interesting stuff you’ve written, curious how it holds up to medical review. Maybe Dr. Greger can offer his knowledge of such matters. Thanks.

          1. Leslie: self-designed, self-administered Alternative Cancer Treatment is not for everyone. One must first and foremost have a compelling reason for avoiding standard treatments and it needs to be more than political, i.e. a desire to avoid supporting the “Cancer Industry.” You need to screen yourself for the following: highly developed self-awareness of one’s cognitive bias (which inc understanding of the cancer industry messaging that goes on all around us from our medical service providers to the media to well-meaning friends and family – most people have lost their ability for independent thought and most importantly, have dulled or non-existent self-biofeedback ability (being able to accurately read body trouble lights and to know what to do)….the other thing is you need to have a highly developed research capability and even though I think we have entered The Last Days Of The Internet As We Know It, an astute mind can discern correctly and construct a cancer self-treatment which rivals what will cost you tens of thousands of dollars to purchase at the best Alternative Cancer Treatment Centers in the world. Paying yourself to do this then becomes the practice for prevention of future problems, as well as the only economic means of accomplishing what you will never be able to afford out-of-pocket unless you are the 1% or have a rich daddy, property to liquidate, or inheritance to forfeit (my highly customized program, which has been shown by conventional medicine to be working, costs a tiny fraction of what it would have cost at the best-in-group Alternative Cancer Treatment program I could find. What I have done is to prove is that if I can do this on a SS check, living in a barn, having other co-existent medicals dragging me down (TBI/dementia, lifelong immune damage from experimental prescriptions, kidney/liver failure) – then anyone can do this. But you must first believe in your ability, must be ready to let go of the spin messages around Cancer and you need to reach out and create supportive coaches and teachers and cohorts whereever possible. Again, so long as the Internet exists for us it is the lifeline.

      1. Hi Eileen:
        why don’t you contact me offsite at my regular email address – there are literally thousands of us in NA alone, doing this. We need to increase our interaction and information sharing. My regular email address is my name at yahoo, without the caps or spaces: Ariel Gail MacLean

  3. I read an article that stated that just the smell of grapefruit can cause a person to suppress their appetite. Could it be that grapefruit may cause weight loss due to this rather than the effect it may have on the metabolism?

    1. I am not sure by just smelling grapefruit it would have that effect. Feel free to post the article if you stumble across.

      1. Olfactory stimulation with scent of essential oil of grapefruit affects autonomic neurotransmission and blood pressure.
        Tanida M1, Niijima A, Shen J, Nakamura T, Nagai K.

  4. People eat grapefruit differently, I know some who add sugar to their grapefruit. The study was not specific in that regard.

    1. Good point! Sugar on grapefruit (the way my grandmother made it for me when I was younger) is not the best idea. In the study Dr. Greger references I don’t think they told participants to use sugar.

  5. Surely the grapefruit accounts for something? Were the subjects given the same food for the rest of the day? And do all of them have healthy metabolisms? And exercise?

    1. Hi Johan. The articles can be found within the links. Researchers usually try to control for factors like exercise and diet. I think grapefruit is a fine fruit to consume and like others it provides an abundance of phytonutrients and vitamins, but the idea of this blog is that 1) it’s not a miracle weight loss fruit, and 2) those taking prescription medication need to be cautious.

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