Grapefruit juice can interfere with statins, blood pressure tablets and antidepressants, making the drugs less potent or increasing the risk of adverse reactions, according to a pharmacist.
Ian Budd, a prescribing pharmacist at internet pharmacy Chemist4U, said grapefruit is the biggest culprit for medication interactions because it contains natural chemicals that block an enzyme in the liver which helps break down certain medicines.
How grapefruit affects medication
Budd explained that when the enzyme is blocked, the body cannot process the drug as it normally would, so more of it stays in the system. This can make side effects stronger or more likely.
He said: "Grapefruit is the biggest culprit for medication interactions. Grapefruit and grapefruit juice are one of the most common causes of food and medicine interactions. They contain natural chemicals that block an enzyme in your liver, which helps break down certain medicines."
He added: "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."
Who should avoid grapefruit juice
The warning is especially relevant for people taking statins, blood pressure tablets, some antidepressants or immune-suppressing drugs. Even one glass of grapefruit juice can have an effect lasting up to one day, so it is safest to avoid it completely with these medications.
NHS guidance backs this up. The health organisation warns on its website that people taking statins should be careful about consuming grapefruit juice. Around eight million people across the UK are currently prescribed statins, which are designed to lower levels of low-density lipoprotein cholesterol, commonly known as "bad" cholesterol.
NHS advice states: "Grapefruit juice can affect some statins and increase your risk of side effects. A doctor may advise you to avoid it completely or only consume small quantities."
Blood pressure medication and other interactions
The health service also highlighted that amlodipine, a widely used blood pressure treatment, can be affected by grapefruit consumption. It said: "Having large amounts of grapefruit or grapefruit juice can increase the concentration of amlodipine in your body and make side effects worse. If you are affected, you may have to avoid eating grapefruit or drinking grapefruit juice while taking amlodipine."
Patients are advised to tell their doctor if they experience increased side effects such as feeling dizzy, flushing or getting headaches after eating grapefruit or drinking grapefruit juice. Otherwise, they can eat and drink normally while taking amlodipine.
Budd noted that foods high in vitamin K can impact how blood thinners work, and that even choices people consider healthy, like fruits, vegetables or supplements, can affect how medication works or how well the body absorbs it. Anyone with concerns about their medication should seek advice from their GP.
