Revealed: The baffling drug interactions you NEED to know about – and it’s not just grapefruit juice and statins to watch out for…

If you take more than one medication, you’ve probably been warned about dangerous drug interactions that you should avoid.

But you may not be aware that it’s not just that we need to be careful about mixing medications… And it’s not just grapefruit juice and statins.

Grapefruit juice and statins

Statins are medications commonly prescribed to help prevent heart attacks and strokes.

They help lower LDL cholesterol, the ‘bad’ type.

Elevated levels in the blood can harden and narrow the arteries.

People advised to take statins are also often encouraged to make healthy changes to their lifestyle, such as adding more fruits and vegetables to their diet.

But there’s one fruit that people taking statins should be wary of: grapefruit.

According to the NHS, a doctor may advise patients taking statins to stop eating and drinking grapefruit. Others may be encouraged to consume only small amounts.

Dr. Leyla Hannbeck, chief executive of the Association of Independent Multiple Pharmacies, said: ‘Grapefruit juice should be avoided when taking cholesterol-lowering medicines such as statins as it prevents an enzyme from being metabolised in the body that is required for the statins.

“As such, it can cause these medications to build up and increase the likelihood of side effects.”

Side effects of statins can include headaches, dizziness, muscle pain and fatigue, according to the NHS.

Warfarin and leafy greens

Warfarin is used to prevent and treat blood clots and has been commonly prescribed in Britain since the 1950s.

While we are all encouraged to eat more leafy greens such as broccoli and spinach, those taking the drug should be careful with these vegetables, experts say.

‘Some green vegetables such as kale, broccoli and spinach that are rich in vitamin K may reduce the effects of warfarin,’ warned Dr Hannbeck.

‘Warfarin blocks an enzyme that uses vitamin K,’ explains pharmacist and lecturer Dr Dipa Kamdar at Kingston University in London.

‘Green leafy vegetables contain quite a lot of vitamin K. This works with the warfarin and speeds up its removal from the body.

‘This means that patients who use this are at increased risk of stroke.’

If you want to change your diet, tell your prescriber so they can adjust your warfarin dose, experts say.

Warfarin and cranberry juice

It’s not just leafy greens that warfarin patients should pay attention to.

A refreshing glass of cranberry juice and eating cranberries can also get them into trouble.

This interaction has the opposite effect of the vitamin K interaction. Instead of preventing the drug from working, it worsens its effects.

As a result, patients may experience unexpected or excessive bleeding.

‘The reason why pharmacists recommend not drinking grape juice if you are taking warfarin is because warfarin thins the blood and grapefruit juice increases the effect of warfarin, leading to an increased risk of bleeding,’ says Dr Hannbeck.

St. John’s wort and the contraceptive pill

St John’s wort is a popular herbal medicine available without a prescription as a treatment for people suffering from depression, although the NHS does not recommend it for this use.

It is often assumed that it is harmless simply because it is a herbal medicine, but pharmacists warn that this is not always the case.

St. John’s wort is an enzyme inducer, meaning it can speed up the breakdown of other substances.

One of those substances is the contraceptive pill.

Dr. Kamdar said: ‘Many people think that St John’s wort is harmless because it is a herbal product, but it speeds up the breakdown of the contraceptive pill in the body.

‘They both work on the same enzyme and it speeds up the speed of this enzyme. This reduces the concentration of the contraceptive pill in the body and may not work properly.’

As a result, combining the two increases the chance that someone taking the birth control pill will become pregnant.

Pharmacists also warn that St. John’s wort can, somewhat counterintuitively, worsen depression if a person is already taking medication for the mental illness.

Dr. Hannbeck added: ‘St John’s wort also interacts with some antidepressants, such as the SSRI, and may increase the risk of side effects and should therefore be avoided during treatment.’

Antidepressants and ibuprofen

Herbal medicines aren’t the only interaction that people taking antidepressants need to be aware of.

One type of antidepressants, called selective serotonin reuptake inhibitors (SSRIs), have a potentially dangerous interaction with anti-inflammatory medications, such as the commonly used over-the-counter painkiller ibuprofen.

Dr. Kamdar said: ‘SSRIs and anti-inflammatory painkillers, such as ibuprofen, can both increase the risk of bleeding, usually in the stomach.

“So taking them together may increase the risk of that.”

According to the NHS, stomach bleeding can cause dark stools, stomach cramps and feeling tired and dizzy.

People taking SSRIs should consult their doctor or pharmacist before using anti-inflammatory painkillers.

Antibiotics and alcohol

Pharmacists will of course encourage people not to drink alcohol while taking antibiotics.

But this is especially emphasized in those taking the antibiotic metronidazole, which is usually prescribed after dental surgery.

Dr. Hannbeck warned that mixing the two could cause side effects including vomiting and flushing, known as a “disulfiram-like reaction.”

The NHS says: ‘Do not drink alcohol while you are taking metronidazole, including for two days after you have finished. This gives the medicine time to leave your body.

‘This is important because metronidazole can react with alcohol and cause a number of side effects. This includes nausea and vomiting, stomach pain, hot flashes, a pounding heartbeat (palpitations) and headache.’

Calcium and antibiotics

Calcium supplements are often taken by older people to strengthen bones and prevent fractures.

But instead of improving your health, calcium supplements can actively harm it by interacting with various medications, pharmacists warn.

These range from antibiotics to medications used to prevent people from getting malaria.

Dr. Kamdar said: ‘These types of interactions take place in the stomach and involve the absorption of the medication.

“So there are certain things like this calcium that you have to be careful with if you’re taking them with certain other medications.”

Antibiotics such as doxycycline, which is often prescribed for acne, are affected if you take calcium supplements, pharmacists warn.

But this is not only the case with calcium supplements, but also with foods rich in minerals, such as milk, cheese and even yogurt.

Dr. Hannbeck said drugs belonging to the class of antibiotics called tetracyclines, which includes doxycycline, are particularly vulnerable to this interaction.

“The calcium in dairy products can reduce the effect of these antibiotics by affecting their absorption into the body,” she says.

But Dr. Kamdar added that there are ways to still get your calcium without affecting your antibiotics.

“Because this interaction takes place in the stomach, the key is to maintain a time difference of about an hour,” she says.

Alcohol and antihistamines

Antihistamines are medications often used to relive symptoms of allergies, such as hay fever or reactions to insect bites.

According to the NHS, some antihistamines such as chlorphenamine, diphenhydramine and hydroxyzine make you feel sleepy.

Side effects of these medications include impaired coordination, reaction speed, and judgment, as well as drowsiness.

And mixing it with alcohol can make these symptoms even more extreme, warns Dr. Kamdar.

She said, “You shouldn’t mix alcohol with those sleepy antihistamines at all because they can make you very sleepy.”