Why mixing grapefruit with antidepressants can be dangerous

By Lauren Wilkin

Summer is here, and amid the sweltering temperatures, many of us are finding relief in sipping fruity cocktails and smoothies.

But now a doctor is warning millions of people taking common medications like statins and antidepressants that ingesting grapefruit — a common ingredient in summer snacks and drinks — can have serious consequences.

"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," Dr. Nicole James, a resident doctor based in Illinois, says.

Common cocktails that contain grapefruit include palomas, greyhounds, some margaritas and sea breezes.

"Grapefruit contains natural compounds — primarily furanocoumarins and flavonoids. These inhibit an important enzyme called cytochrome P450 3A4," the doctor, who previously worked for the National Health Service 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," James says.

Having higher concentrations of a medication than normal can cause serious side effects.

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"Patients taking statins could experience higher levels than normal, which can cause muscle breakdown and cramps," James says.

Meanwhile, 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 like sertraline also come with a warning to avoid the fruit.

And you might think it would take a lot of grapefruit to have an effect, but James says this isn't the case.

"As little as one grapefruit or 200 milliliters of juice can cause a clinically relevant increase in medication concentrations, and the effect can last up to 72 hours because grapefruit irreversibly inactivates the 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," James says, advising people to always seek medical attention if there are any concerns.

The doctor also warns of the following ingredients that patients should be aware of:

• Vitamin K-containing ingredients, such as leafy green vegetables or cranberry juice, if taking warfarin — commonly prescribed for reducing the risk of heart attack and stroke
• Dairy-containing products can reduce the effectiveness of certain antibiotics, such as ciprofloxacin and bisphosphonates (like alendronate, which is often taken for osteoporosis prevention)
• Herbal remedies that can inhibit or increase activity of the CYP3A4 enzyme, such as St. John's wort and goldenseal