Grapefruit, and some other varieties of citrus fruit, are off the menu for a lot of people using common medications.

But a new study might help to develop safe varieties.

Grapefruits, as well as pomelos and bitter oranges, contain compounds that interfere with the action of a number of different drugs prescribed for conditions like cholesterol, high blood pressure, and anxiety.

These medicine-inhibiting compounds are called furanocoumarins. People prescribed these medicines are usually instructed to avoid grapefruits and grapefruit juice.

A study published in New Phytologist has found the genetic source of furanocoumarins.

The researchers examined the genomes of ancestral citrus species, as well as crosses between mandarins, grapefruits, and pomelo.

They found that a single gene in citrus fruit controlled whether or not the fruit produced furanocoumarins.

The gene belongs to a large group called the 2-oxoglutarate-dependent dioxygenase family, which codes for enzymes that make a range of biological molecules in plants.

“This research helps us to understand why fruit of certain citrus species produce furanocoumarins and demonstrates how breeders and researchers could develop furanocoumarin-free citrus varieties,” says co–corresponding author Dr Yoram Eyal, a researcher at the Volcani Center in Israel.

The researchers say that a medication-safe grapefruit could be cultivated via either genetic modification, or marker-assisted breeding, to knock out the problematic gene.