A doctor is warning millions of people taking common medications like statins and antidepressants that eating or drinking one specific fruit can have serious consequences. Natural compounds in the fruit interfere with common medications, and can make them dangerous.
"Grapefruit is a pleasant snack for most but it is important to disclose large amounts of grapefruit use to your doctor because it can interact with an array of medications," said Dr Nicole James, a resident doctor based in Illinois.
How grapefruit affects medication
"Grapefruit contains natural compounds — primarily furanocoumarins and flavonoids. These inhibit an important enzyme called cytochrome P450 3A4," the doctor who previously worked for the NHS in London, explains. This enzyme is referred to as CYP3A4. It plays an important role in breaking down oral medications so your body can properly process them.
"When you ingest grapefruit it blocks this enzyme," explains the doctor, who is also a clinical research fellow in the Department of Dermatology at Stanford University.
"This causes drugs that would normally be broken down in the gut wall to instead pass through intact, leading to significantly higher-than-intended blood levels of the medication," Dr James says. Having higher concentrations of a medication than normal can cause serious side effects.
Risks for statin and blood pressure patients
"Patients taking statins could experience higher levels than normal which can cause muscle break down and cramps," Dr James says. While patients taking certain blood pressure medications like amlodipine "may experience dizziness and low blood pressure."
Sedatives can also pose a risk, with medications like midazolam being impacted by grapefruit and causing "extreme drowsiness and even slowed breathing."
Antidepressants and lasting effects
Antidepressants like sertraline also come with a warning to avoid the fruit. "As little as one grapefruit or 200 mL of juice can cause a clinically relevant increase in medication concentrations, and the effect can last up to 72 hours because grapefruit irreversibly inactivates CYP3A4 enzyme," she says.
For this reason, she says people should keep an eye on mixed fruit juices, smoothies and cocktails this summer as grapefruit juice is a common ingredient. "If a patient ingests a large amount of grapefruit while on these medications they should monitor for any symptoms and avoid ingesting any more grapefruit," Dr James says, advising people to always seek medical attention if there are any concerns.
Other ingredients to watch
- Vitamin K containing ingredients such as leafy green vegetables or cranberry juice if taking warfarin - commonly prescribed for reducing risk of heart attack and stroke
- Dairy containing products can reduce the effectiveness of certain antibiotics such as ciprofloxacin and bisphosphanates (like alendronate often taken for osteoporosis prevention)
- Herbal remedies that can inhibit or increase activity of the CYP3A4 enzyme like St Johns Wort and Goldenseal
A full list of medications that grapefruit interferes with can be found at the BNF website.
