Five healthy diet staples that may interact with prescription drugs

One of the most popular new year’s resolutions is making a commitment to healthier eating. Whether that’s eating more fruits and vegetables, cutting down on meat consumption or even becoming a vegetarian or vegan a few days a week.

While there are many benefits that can come from following a healthier diet, it’s important that any diet changes are made carefully. This is especially true if you’re someone who takes a prescription drug, as many health food staples can negatively interact with them.

Here are some common foods and drinks interactions you should know about:

1. Grapefruit juice:

To break down some prescription drugs in the body, the liver uses enzymes called cytochrome P450. But grapefruit juice contains chemical compounds called furanocoumarins which can block the action of these enzymes. If this happens, some drugs can accumulate in the body.

This includes ciclosporin, a drug that’s commonly used to prevent organ transplant rejection and manage symptoms of rheumatoid arthritis and skin conditions such as psoriasis. A build-up of ciclosporin can cause many side-effects, ranging from mild nausea and vomiting to kidney and liver damage.

Statins, often used to treat high cholesterol levels and prevent heart attacks and strokes, can also be affected by grapefruit juice through the same mechanism. Increased statin levels in the body can raise the risk of side-effects, including muscle breakdown, which is rare but serious.

Many other drugs can potentially interact with grapefruit juice as well – including amlodipine (a common high blood pressure drug) and sildenafil (an erectile dysfunction drug). If you take any of these prescriptions drugs, it’s best to talk to your doctor or pharmacist before drinking even small amounts of grapefruit juice. It may even be best to avoid it altogether.

2. Pomegranate and cranberry juice:

Many fruits and fruit juices – especially from the citrus family – can affect the breakdown of drugs in the liver.

Pomegranate juice is also shown to block the liver enzymes which break down the anticoagulant drug warfarin. The drug is used to prevent blood clots from forming in people with heart arrhythmias such as atrial fibrillation or deep vein thrombosis.

Some reported cases suggest that pomegranate juice might increase the international normalised ratio (INR – the time taken for blood to clot) in patients taking warfarin. This means patients may be at higher risk of bleeding.

Pomegranate juice may also affect other drugs, such as tacrolimus, an anti-rejection drug used in organ transplants.

Similarly, a number of case reports suggest cranberry juice can also affect warfarin. There has been one reported death of a patient from bleeding after they had drunk cranberry juice for two weeks prior while taking warfarin.

But results from various studies are mixed – with some showing cranberry affects warfarin in the body while others don’t show any effect. Because of this, it may be worth checking the INR more often if you drink these juices or consider that any fluctuations in INR may be due to fruit juices.

3. Green leafy vegetables:

Spinach, broccoli and kale are often hailed as healthy foods because they’re filled with nutrients while being low in calories. However, they’re also high in vitamin K, which is needed to activate certain clotting factors (proteins in the blood which help it clot).

This may be problematic for patients taking warfarin. Warfarin works by blocking vitamin K in order to prevent blood clots from forming. But eating foods rich in vitamin K can lower your INR and increase the risk of developing a blood clot.

It’s important to have a healthy diet – but be sure to monitor your INR levels or speak to your doctor if you do introduce more vitamin K-rich foods into your diet.

4. Milk:

Milk and dairy-rich foods such as cheese and yoghurt are all good sources of protein and calcium – a mineral required for healthy bones.

But these foods can affect the absorption of some drugs in the gut. This includes antibiotics such as some tetracyclines and ciprofloxacin. The calcium in the milk can bind to the antibiotic, meaning it cannot be absorbed into the bloodstream. This means the body will not get the full dose of antibiotic – making it harder for it to fight the infection.

Other drugs affected by dairy include levothyroxine, a drug used for patients with low thyroid levels.

But as these interactions happen in the gut, this means you can still have dairy even if you take these drugs. In most cases, you just need to leave at least a two-hour gap either before or after taking the drug before consuming dairy.

5. Beans:

Beans are considered healthy as they’re high in fibre and vitamins and minerals. Beans are also a great source of plant-based protein.

But soybeans, broad beans (fava beans) and snow peas may be high in tyramine. While tyramine is a substance naturally found in the body and in certain foods (such as aged cheeses, cured meats and fermented foods), it can interact with the antidepressant phenelzine.

Phenelzine is a monoamine oxidase inhibitor antidepressant (MAOI), which is less commonly used nowadays. The drug blocks enzymes which break down tyramine in the body. If patients eat tyramine-rich foods, this may result in high levels of tyramine, potentially leading to a dangerous rise in blood pressure. Only MAOI antidepressants, such as phenelzine, isocarboxazid, tranylcypromine, are affected by tyramine.

A healthy diet can improve your overall health in many ways. Just be sure to consult with a doctor of pharmacist before drastically changing your diet – particularly if you take prescription medications.

Dipa Kamdar does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.