Food and drink are two of the most important factors undermining the effectiveness of many prescription and over-the-counter drugs. It’s a common problem, but not as well known as it should be.
That’s because few of us really stop to think that deeply about how our body’s digestion process actually works. Yet what we eat or drink can speed up, or slow down how quickly drugs are absorbed, making them less effective or even toxic in certain cases. Food and drug interactions can also produce entirely new and unwelcome side effects altogether.
Take licorice root from the glycyrrhiza glabra plant. It’s an ancient remedy for stomach issues and stress. But it doesn’t mix well with high blood pressure medications because of the way that it lowers potassium levels in the body, causing electrolyte imbalances and heartbeat abnormalities.
Taking too much even without medication is not a good idea either. Only last month, the New England Journal of Medicine reported the case of a 54-year US construction worker who collapsed and died from a heart attack after a few weeks of eating a bag-and-a-half of licorice candy per day. It’s an extreme example with a wider message about the need for care.
When it comes to taking any kind of medication, it’s incredibly important to read the label carefully. If in doubt, ask a pharmacist for advice. We’ve also created a checklist of some of the commonest healthy foods, which can cause issues in combination with certain drugs:
1. Citrus fruits
They’re loaded with vitamin C, but they also contain furanocoumarins, which inhibit enzymes that metabolise some medications. The biggest culprits are grapefruit, orange, apple, pomelo and star fruit. Studies show that grapefruit juice can halve the effectiveness of anti-histamines such as fexofenadine as well as antibiotics including ciprofloxacin, levofloxacin, itraconazole (anti-fungal) and isoniazid (TB).
Fruit juice isn’t a great mixer either for high blood pressure medications like atenolol, celiprolol and talinolol, nor high cholesterol drugs like atorvastatin, simvastatin and lovastatin.
2. Green leafy vegetables
They’re a superfood, replete with a multitude of beneficial minerals and vitamins. One of these is vitamin K, which aids bone health and blood clotting. But that’s not good for people taking blood thinners like warfarin. So avoid eating spinach, kale, cos lettuce, Brussels sprouts, broccoli or parsley within two hours of taking the drug, or up to six hours afterwards. Cooked onions, on the other hand, have the opposite effect.
Cruciferous vegetables also affect the absorption of some painkillers like acetaminophen (paracetamol).
3. Dairy products
Calcium reduces the absorption rate of certain antibiotics because of a process called chelation: calcium ions create an insoluble compound when they interact with tetracycline antibiotics like doxycycline and linezolid (pneumonia and MRSA). Again avoid eating up to two hours before or six hours after taking the drug.
4. Aged and fermented foods
These contain high levels of tyramine, which the body breaks down through the monoamine oxidase (MAO) enzyme. Too much tyramine narrows blood vessels, leading to high blood pressure. So people taking antidepressants and anti-anxiety medication containing MAO inhibitors like phenelzine and tranylcypromine should avoid these foods.
Examples include dried fruit, overripe fruit such as bananas, aged cheeses, shrimp paste, smoked fish, cured meats, yeast extract, fermented and pickled foods like miso, tofu, kimchee, kefir and sauerkraut, plus fermented alcoholic beverages like beer, red wine and sherry.
5. Caffeine
It’s a stimulant that affects the central nervous system and increases breathing rates.But it can also increase unwelcome side effects such as nausea, tremors and insomnia if it’s taken alongside bronchial medications for asthma and chronic obstructive pulmonary disease such as theophyline.
Less healthy caffeinated beverages such as fizzy drinks should also be avoided with painkillers like ibuprofen. The carbon dioxide, which makes them fizzy, damages the pill coating, speeding up the drug’s release.