Research shows most of us don’t feel confident that we’re taking prescribed medications correctly — here experts reveal one key piece of advice you should watch out for.
When prescribing medications, doctors often dish out basic instructions like “don’t drink alcohol” and “take with meals”. These rules usually focus on things like timing, dosage, consistency and alcohol consumption.
However, we should also be cautious about the foods and non-alcoholic drinks we consume alongside medications, as certain foods can interact with them in ways that may harm the body, leading to potentially serious consequences.
Unfortunately, these interactions and their potential risks are far lesser known to the general public. In a recent survey, only 32% of patients reported having a good understanding of their medications and 55% said they had trouble reading the patient information leaflet provided.
“Drug interactions with food are far more common than you might think, particularly in elderly people,” warns Dr Deborah Lee from Dr Fox Online Pharmacy. In one 2023 study, 40.4% of elderly patients admitted to hospital had at least one dangerous drug interaction (DDI).
There’s one food in particular that experts advise avoiding at all costs.
What food should be avoided when taking medication?
Grapefruit should be avoided when beginning any course of medication. This is because it’s a “moderate Cytochrome P450 (CYP) inhibitor”, says Dr Lee.
Grapefruit or grapefruit juice contains a set of compounds called furanocoumarin, which can inhibit enzymes found in the liver that are responsible for about 90% of drug metabolism and breakdown.
Breakdown products are excreted from the body in urine or faeces, but when this process is inhibited, for example, by grapefruit, “the body is no longer able to metabolise certain medications,” explains Dr Lee. As a result, “the concentration of the specific drug rises in the bloodstream, sometimes to dangerous levels.”
What happens when you eat grapefruit while taking medication?
As mentioned above, ingesting grapefruit or grapefruit juice while taking any of these medications can inhibit the CYP enzymes needed to break down these drugs. As a result, Dr Lee explains, “higher drug levels will be present in the bloodstream.”
This can lead to serious toxic effects, which vary depending on the medication. But Dr Lee warns, “the effects could be similar to having an overdose.”
For example, if felodipine, a blood pressure medication, is not metabolised properly after eating grapefruit, “blood pressure could drop too much, leading to dizziness and fainting,” says Ana Carolina Goncalves, superintendent pharmacist at Pharmica.
Another dangerous example would be when taking the cholesterol medication simvastatin alongside grapefruit. Ana Carolina explains: “The inhibition of CYP3A4 can cause muscle pain, weakness, and, in extreme cases, kidney damage due to muscle breakdown (rhabdomyolysis).”
For the accumulation of sedatives and opioids like diazepam and oxycodone, this can lead to “excessive drowsiness, confusion and slowed breathing”, she adds.
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Abbas Kanani, superintendent pharmacist at Chemist Click also highlights that grapefruit can increase the absorption of blood pressure medications, like calcium blockers, “causing blood pressure to drop to a dangerously low range.”
Grapefruits can also increase the amount of statins in the blood. This is because they “contain a chemical that interferes with the enzymes that break down statins in your digestive system,” says Abbas. “This can increase the risk of serious side effects for people taking statins for cholesterol including damage to the liver, muscle breakdown and kidney failure.”
Additionally, grapefruits can also make some antihistamines such as fexofenadine less effective by “blocking the way enzymes and transporters in the small intestine work,” he explains.
Which medications are affected?
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Below, Ana Carolina provides a list of potential side effects with popular medications to be aware of:
- Felodipine and amlodipine can cause excessively low blood pressure, dizziness and fainting.
- Simvastatin, atorvastatin and lovastatin can cause muscle pain, weakness and kidney damage (rhabdomyolysis).
- Sildenafil can increase the risk of headaches, flushing, dizziness and low blood pressure.
- Diazepam and midazolam can cause excessive sedation, drowsiness, confusion and slowed breathing.
- Oxycodone can cause extreme drowsiness, respiratory depression and an increased risk of overdose.
- Cyclosporine and tacrolimus can increase immunosuppressive effects and lead to kidney damage.
Although harmful side effects may occur while taking these medications, “it’s unlikely anyone would eat enough grapefruit over a sustained period of time for it to be life-threatening,” Dr Lee concludes. But still, she advises: “It’s always wise to avoid eating it to be safe.”
The above is not a complete list and you should always consult your GP or pharmacist for advice before taking any medication.
