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rapefruit, kale — foods like these have health benefits. But if paired with certain medications, the good stuff we eat can spike our blood pressure, dull our motor skills, cause an overdose, or worse.

Medications work on time curves and half-lives, and for many, there are narrow lines between just the right amount and either not enough or way too much.

When it comes to don’t-take-these-together guidance, there’s a long list of potentially dangerous combinations. Here are four foods we consume that can interact with common medications, and what they do to us when we mix them.

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Grapefruit

If you eat grapefruit or drink grapefruit juice at all, be aware that the fruit interacts with several classes of drugs, including statins (taken to lower cholesterol), beta blockers (used to treat heart disease and regulate blood pressure), immune suppressing drugs, psychotropic drugs, and even certain anesthetics.

Grapefruit juice contains compounds called furanocoumarins, a natural part of a plant’s defense mechanisms. Furanocoumarins, a few in particular, can block the effect of an enzyme in the liver and small intestine that deactivates drugs and other foreign chemicals. Drugs can end up circulating in their active state for much longer than expected and a person taking them can effectively be overdosed.

Other compounds in grapefruit juice seem to mess up certain cell-surface transport molecules, potentially blocking a drug from getting into a cell, or keeping it from getting out. The net effect? Too much or too little circulating in your bloodstream.

Kale

This foodie favorite is full of vitamin K, which we need to make blood clots. But if you are taking the blood thinner warfarin because of, say, a heart attack, arterial blockage, or heartbeat irregularities, you have to be careful not to overdo it with kale and cruciferous veggies like Brussels sprouts and broccoli.

Warfarin prevents the body from using vitamin K to make clotting factors. The excess vitamin K that might come from a sudden interest in kale salads could make warfarin’s job that much harder.

In addition to kale and broccoli, there are several research studies exploring the interaction of warfarin and cranberry juice. Turns out compounds in cranberries called flavonoids can block detoxifying enzymes similar to the way grapefruit furanocoumarins do.

Cheese

Cheese comes in so many varieties, from fresh burrata to the stinkiest aged blues. Dairy products can interact with several drugs, but aged cheeses in particular are a big no-no if you are taking monoamine oxidase inhibitors, a class of antidepressants.

Fermented, cured, and aged foods are often packed with tyramine, a chemical that causes blood vessels to narrow. MAOIs block the breakdown of tyramine, so as it builds up, so does blood pressure.

And the effect lasts — people who stop taking MAOIs are told to avoid tyramine-rich foods for days to weeks after.

Bananas

These fruit are rich in potassium, an element essential to heartbeats and neurotransmitter movement. Potassium ions are associated with channels and pores in cell membranes that allow things in and out of a cell.

For people with high blood pressure on a class of drugs known as ACE inhibitors, which block the conversion of an inactive molecule to one that powerfully constricts blood vessels, one of the common side effects is a buildup of potassium. Eating foods like bananas and kale, both of which are high in potassium, can make that buildup worse.

But ACE inhibitors aren’t the only drugs that play a role in our bodies’ potassium balance. Some diuretics affect the way our kidneys get potassium out of the body.

What’s the harm in a little extra potassium? Excess potassium can mess up your heartbeat and other biological functions.

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  • Tssk, STAT, don’t add to the pile of panicky stories on single food items and drugs out there. I’m suprised that doses are not mentioned at all. How many grapefruits does one have to eat for adverse side-effects occur?
    For inspiration: doi: http://dx.doi.org/10.1136/bmj.f1 (Published 07 January 2013)

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