Guide

Drug interaction alert! Foods and medicines that don’t go together

17/10/2023

Translation: Katherine Martin

Medicine is supposed to get us healthy, but we often unknowingly sabotage its effects. How? Through our diet. In the most severe cases, this can even be fatal.

Medications have an impact on our bodies. To achieve the best possible impact, however, they have to be taken under optimal conditions. Most of us are aware that taking multiple medications at once can lead to drug interactions. It says so on the labels, after all.

What’s less well known is that some foods, drinks and even dietary supplements can also alter the effects of your medication if they’re taken in too quick succession (linked article in German). In fact, their effects might be cancelled out altogether, significantly reduced or become far too strong. This can ramp up unpleasant side effects and trigger undesirable drug reactions, some of which might even be dangerous.

So why is this the case? «Every single meal we eat contains several hundred potentially interacting chemical compounds,» explains Dr Günther Schwarz, a Medications and Food lecturer at Akademie des Verbands für Unabhängige Gesundheitsberatung (The Academy of the Association for Independent Health Counselling) (website in German). As a result, food components can bind medications’ active ingredients, delaying or even preventing their absorption. Not only that, but food composition can alter the transportation of the substance, its absorption rate and bile acid and liver metabolism.

Be careful with grapefruit

In the 1990s, scientists accidentally discovered that grapefruit affects the impact of certain drugs. During a clinical study, researchers gave participants a drug to be taken with grapefruit juice. Though the pills tasted better, their active ingredients didn’t break down, doubling their typical concentration in the body.

Based on this chance finding, scientists at Canada’s Lawson Health Research Institute conducted further research. In 2013, it published a list of 85 drugs that should never be taken with grapefruit juice. These include cholesterol-lowering drugs, painkillers and oral contraceptives containing oestrogen.

Possible adverse reactions include skin rashes, dizziness, headaches, breathing difficulties, and even reduced blood pressure, severe kidney damage, muscle breakdown and sudden cardiac arrest. Because of this, numerous medications now come with a «grapefruit warning».

Inadequate package inserts and instructions for use

Unfortunately, the instructions for use included with medications often fail to provide adequate information on risky combinations of foods and medicines.

Reason 1: many interactions are simply not (yet) known.
Reason 2: even when the package inserts do contain information, the warnings are often incomprehensible to laypeople.

Numerous tragedies have resulted from this. Bern’s Dementia Journal, for example, reported on the case of a 70-year-old man who, having lost his appetite after a bout of pneumonia, attempted to nurse himself back to health by drinking large quantities of cranberry juice. Six weeks later, he was dead. A study into the probable cause of death concluded that the enzyme that breaks down the drug warfarin had been inhibited. Flavonoids (secondary plant compounds) in the otherwise healthy cranberry juice had multiplied the effect of the anticoagulant the man had been taking for years. As a result, he suffered fatal internal bleeding.

Even Germany’s «Gelbe Liste Pharmaindex» (website in German), a directory listing more than 27,000 medicines and containing all the important information on indications, contraindications and interactions, doesn’t mention the link between cranberries and warfarin. It only warns against consuming large quantities of lingonberries (page in German).

Drug interactions: from alcohol to vitamin K

Of course, the interaction between food, drink and drugs isn’t always that drastic. Even so, you should watch what you eat if you’re taking medication. Using the «Gelbe Liste» directory as a reference, I’ve summarised the most common food-drug interactions (besides grapefruit):

Alcohol: It goes without saying that you should stay off the booze when taking medication. Alcohol depresses the central nervous system, exaggerating the effect of drugs such as antidepressants, sleeping pills and tranquillisers. Not only that, but larger quantities of it prevent your body from breaking down and excreting medications. As a result, the effects of the drugs become more potent. This has a detrimental impact on concentration and reaction times – a consequence that isn’t just dangerous on the roads. After all, alcohol also amplifies the effect of diabetes medications and anticoagulants.

Fibre: Though otherwise a healthy substance, fibre from vegetables, fruit and whole grains can bind some drugs. Because it swells when it’s exposed to moisture, it can also inhibit their absorption. This can make some drugs less potent. Examples include acetyl salicylic acid (ASA), levothyroxine (L-thyroxine) for the treatment of hypothyroidism, digoxin for weak heart muscles and cardiac arrhythmias, and certain types of penicillin. So don’t take any of these tablets with foods such as cereal or dairy products.

Calcium + dairy products: Calcium can diminish the absorption of drugs. If it’s taken in conjunction with medication for iron deficiency, bone loss, infections or thyroid conditions, the drugs won’t achieve their maximum effect. If you take medications like these, you should wait at least two hours before eating dairy products. You’d also be advised to avoid mineral water enriched with calcium (and/or iron).

Caffeine: A number of medications and oral contraceptives interfere with the metabolism of caffeine, causing caffeine levels in your blood to go up. The consequences of this range from sleepless nights and restlessness to increased urination and cardiac arrhythmias. Caffeine also inhibits the metabolism of theophylline, which is used to treat bronchial asthma or chronic bronchitis. If you’re taking iron tablets, you shouldn’t drink anything with caffeine in it. This is because the tannins in coffee and tea clump together with the iron in the stomach to form insoluble compounds that the body doesn’t absorb. Some drugs used to treat psychiatric disorders, referred to as neuroleptics, are also less effective when consumed with drinks like black tea.

Protein + protein-rich foods: Protein is made up of numerous small building blocks called amino acids. Your body also produces amines. If you’re taking medication designed to interfere with the metabolic cycle of amines produced within your body, the drugs will also interact with the amines from protein-rich foods such as meat, fish, dairy products, eggs or legumes. This impairs the effect of the drugs. In other words, cheese and similar products can be problematic if they’re mixed with, say, antidepressants or tuberculosis medication.

**Fatty foods: **Meals with a very high fat content may lead to varying effects if eaten at the same time as taking medication. Sometimes, the fat covers the inner lining of the intestinal tract like a film, slowing down or reducing the absorption of the drug. It can, however, have the opposite effect too. The absorption of some drugs significantly increases when taken together with fatty food. And fat-soluble active ingredients are also better absorbed.

**Fruit juices, acidic drinks and vitamin C: **Acidic foods and drinks like soda pop, champagne, wine, fruit juices or vitamin C affect the gastrointestinal absorption of amphetamine-containing drugs. Examples of these include appetite suppressants and ADHD medications. Not only that, but fexofenadine levels are lowered when taken with fruit juices. The result? That antihistamine you took for your hay fever won’t work quite as well.

**Liquorice: **This particular sweet treat shouldn’t be combined with diuretics – medicines that dehydrate the body. This is all the more important for people with diabetes, hypertension or other cardiovascular diseases, as well as pregnant women. Liquorice can cause you to excrete too much potassium while retaining water and sodium in your body. The consequences of this range from oedema (water retention in the tissues) and an increase in blood pressure to potassium-induced muscle weakness and even cardiac arrhythmias.

**Foods containing tyramine: **Tyramine is contained in high-protein foods stored for a long time, including cheeses, salami, white beans, yeast, (soya) beans, some beers and red wine (especially Chianti). Your body usually protects itself from elevated tyramine levels. If you’re taking the antidepressants known as non-selective MAO inhibitors, however, these drugs can block tyramine breakdown. So you should avoid any foods containing tyramine. Otherwise, your blood pressure can rise to dangerous levels and you may even suffer a fatal brain bleed. MAO inhibitors are also incompatible with histamine, which is found in mackerel and cheddar, for example.

Vitamin K: Vitamin K weakens the effect of anticoagulant drugs, which are designed to prevent thrombosis. It’s found in large quantities in cauliflower, curly kale, broccoli, avocado, spinach, peas, soy beans and even black tea and liver.

Take with water and watch your diet

So what now? Unless the package insert, your doctor or your pharmacist recommends otherwise, it’s best to swallow down your medicine with tap water or low-calcium mineral water. If necessary, you should also avoid the foods and drinks mentioned above.

However, since the list also includes healthy and tasty foods, you should definitely talk to your healthcare provider about your eating and drinking habits. They’ll be able to find a way for you to balance your medications with your diet.

Further research and documentation needed

Not only is there no comprehensive, scientific summary of how frequently food-drug interactions occur and what their consequences are, but many interactions simply haven’t been discovered or documented. «At most, we estimate that only 20 per cent of actual cases are reported,» says Maik Pommer, spokesman for the German Federal Institute for Drugs and Medical Devices.

The organisation encourages anyone who suspects they’ve experienced a drug interaction to report it, either by getting in touch with the Insitute or its Swiss counterpart, Swissmedic. «If more people reached out to us, we’d have a much better understanding of the problem. We’d also be able to give the right warnings on drug packaging or in package inserts.»

Header image: Shutterstock

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Daniela Schuster

Autorin von customize mediahouse

oliver.fischer@digitecgalaxus.ch

If my job didn't exist, I'd definitely invent it. Writing allows you to lead several lives in parallel. On one day, I'm in the lab with a scientist; on another, I'm going on a South Pole expedition with a researcher. Every day I discover more of the world, learn new things and meet exciting people. But don't be jealous: the same applies to reading!

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