• Fermented foods like miso can interact with certain medications. (SBS Food)Source: SBS Food
A new book examines the complex and often dangerous way food, drinks and dietary supplements can interact with medicine.
Nicola Heath

9 Mar 2016 - 2:11 PM  UPDATED 9 Mar 2016 - 2:11 PM

We are often aware of the risks of mixing medicines, but it’s less often that we consider how the medication we take interacts with the food we eat. A new book, Don’t Eat This If You’re Taking That (Nero, $24.99), demystifies the dangerous world of food and drug interactions, explaining the complex chemical processes that happen in our bodies when we take a drug. Alcohol is an obvious example, interfering in the normal action of many common medications by exacerbating side effects like dizziness and drowsiness. Here are some more potentially harmful interactions that the authors, Madelyn Fernstrom and John Fernstrom, uncovered in their research. 

Fermented foods

Health nuts love fermented foods like sauerkraut, kimchi and miso for the important role they play in keeping the gut and its colonies of friendly bacteria in good shape. However, if you are taking a monoamine oxidase inhibitor (MAOI), a ‘first generation’ antidepressant developed in the 1950s, you should steer clear of fermented foods.

Here’s why: when you eat a fermented food like miso, part of the digestive process breaks down the food into amino acids. Some of these amino acids are converted into chemicals known as biogenic amines – tyramine is one - which can cause blood pressure to rise when they enter the bloodstream. This effect is usually countered by an enzyme called monoamine oxidase, which moves in to destroy the amines before blood pressure rises too much. When you take MAOIs this system is switched off, so eating tyramine-rich foods like miso – or cheese and chocolate – can create a hypertensive crisis, which can lead to heart failure.

Grapefruit juice

At last count there were 85 medications known to interact with grapefruit, thanks to chemicals found in the fruit called furanocoumarins. These chemicals affect an enzyme required to metabolise many medicines, potentially allowing more than the intended dose into the bloodstream. Anyone taking medication including antidepressants, analgesics like opioids, some types of triptans (used to treat migraines), anticoagulants, migraine medication including ergotamine, some diabetes medication, and cardiovascular drugs should avoid eating grapefruit and drinking its juice to avoid complications that in severe cases include kidney failure.

St John’s wort

St John’s wort is often recommended as a natural remedy for depression and related disorders, however it is important that people who are taking antidepressant medication leave this supplement on the shelf. Not only does St John’s wort reduce the efficacy of tricyclic antidepressants, it can cause serotonin syndrome, a potential fatal condition caused by toxic levels of the neurotransmitter serotonin in the body, when taken in conjunction with three classes of antidepressants: MAOIs, SSRIs (serotonin-selective reuptake inhibitors) and SNRIs (serotonin-norepinephrine reuptake inhibitors), and some migraine medications known as triptans.

Like grapefruit, St John’s wort interacts with a long list of other medications. These include some opioids including codeine, fentanyl and methadone; diabetes medication like nateginade and pioglitazone; proton pump inhibitors, used to treat acid reflux; blood pressure medicines; the cholesterol-lowering statins simvastatin and atorvastatin; anti-arrhythmia drugs like amiodarone, dronedarone, disopyramide and quinidine, as well as other cardiovascular medications, which all become less effective when taken at the same time as the supplement.


Leafy green vegetables like kale can interfere with the normal action of warfarin, a common blood-thinning drug. Cutting out kale entirely from your diet is a little drastic however; instead people prescribed warfarin should limit their daily intake of leafy greens. The issue is vitamin K, required in the blood clotting process and found in large quantities in vegetables like spinach (145micrograms in 1 cup), kale (113mcg per cup) and broccoli (110mcg a cup). To ensure large amounts of vitamin K don’t interfere with their medication, people on warfarin should go light on leafy greens while they are taking the drug.

Orange juice

Orange juice is a no-go for people taking atenolol, a beta blocker prescribed to reduce blood pressure, as it limits the drug’s absorption in the small intestine. Orange juice also interacts with the anti-arrhythmia drug quinidine. Vitamin C increases the amount of the drug that passes into the urine, thus affecting the final dose.  


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