Drug Interactions: 6 Foods to Watch Out For 

Whether on a short-term course of antibiotics, or a long-term treatment like warfarin, you always want to be taking your medication safely and as instructed. But that can be easier said than done if you’re not aware of the food-drug interactions you can experience on your medication.  

That’s where we come in. We’ve put together a guide on some of the most common food-drug interactions to help you stay safe – the answers may surprise you! 

Three key takeaways 

• A drug-food interaction is when your medication interacts with food or drink, potentially making it less effective or increasing the chance of side effects.   

• Grapefruit is one of the most common causes of food and medicine interactions.  

• Always make sure to read the patient information leaflet for guidance on what to avoid when taking your medication.  

What is a drug interaction? 

A drug interaction is when something interacts with your medication. This can then change how effectively the drug works, or increase the chance of you experiencing side effects. 

There are three main types of drug interactions:  

• Drug-drug interactions: this is when the drug you are taking interacts with another medicine you may be on.  

• Drug-condition interactions: this is when your medication interacts with a pre-existing medical condition you may have.  

• Drug-food interactions: this is when your medication interacts with food or drink.  

Food and medicine interactions 

One of our prescribing pharmacists, Ian Budd, has put together a list of some of the most common foods and drinks that can interfere with everyday medication. 

Grapefruit 

If you enjoy some grapefruit over breakfast, you should be aware that, whether in segments or as a juice, it’s one of the most common causes of food and medicine interactions. 

Grapefruit contains natural chemicals that block an enzyme in your liver that helps break down certain medicines. When that happens, your body can’t process the drug as it normally would, so more of it stays in your system. That can make side effects stronger or more likely.  

This is especially important if you’re taking medicines like statins, blood pressure tablets, some antidepressants, immune-suppressing drugs, or erectile dysfunction pills such as sildenafil or tadalafil. Even one glass of grapefruit juice can have an effect that lasts for up to one day, so it’s safest to avoid it completely with these medications. 

Leafy greens 

Cranberry juice 

Cranberry juice is often seen as a healthy choice, but it can be a problem if you’re taking warfarin. Cranberries contain natural compounds that can affect how your body breaks down warfarin, which may make the drug stronger than intended. That means your blood could become thinner, increasing the risk of bruising or bleeding.  

It’s not an issue for everyone, and an occasional glass is unlikely to cause harm, but drinking cranberry juice regularly or taking cranberry supplements can be risky if you’re on warfarin. It’s always best to check with your pharmacist before making it part of your daily routine. 

Dairy products 

Tyramine-rich foods 

Foods like aged cheeses, cured meats, and fermented products contain something called tyramine. And tyramine can cause a sudden rise in blood pressure if you’re taking older antidepressants known as MAO inhibitors. This type of reaction can make you feel unwell with headaches, a fast heartbeat, or even very high blood pressure.  

These drugs aren’t prescribed as often now, but for anyone taking them, it’s important to know which foods to avoid. Your pharmacist can help you spot tyramine-rich foods and give simple swaps so you can still enjoy your meals safely. 

Alcohol 

Alcohol is one of the most common things that interacts with medications, and the effects can vary depending on what you’re taking. It can make some drugs, like antidepressants, sedatives, and strong painkillers, much more sedating, which can leave you feeling drowsy or unsteady. 

It can also put extra strain on your liver or interfere with how medicines for diabetes work, making blood sugar harder to control. 

And by mixing Viagra and alcohol at the same time, you may reduce the chance of the erectile dysfunction medication actually working.   

It doesn’t mean you can never drink, but it’s always worth checking your patient information leaflet or asking your pharmacist what’s safe for you. Knowing how alcohol might affect your medication can help you make more confident, informed choices.