The adverse interaction between grapefruit and certain medications has been known for some time. But a study released late last year by Canadian researchers now lists 85 different medications, 43 of which could have potentially fatal consequences when mixed with grapefruit.

The list, says Jennifer Reiter, a clinical pharmacist at IU Health Bloomington Hospital, “covers all kinds of drugs, including heart arrhythmia medications, common blood pressure and blood thinner drugs, and most but not all statins [cholesterol-lowering drugs].” It also includes some anticancer drugs, some psychiatric drugs, some estrogen treatments, and drugs taken by transplant patients.

Here’s how the adverse effects occur: There is a group of enzymes in our gut that metabolize, or break down, drugs. Grapefruit blocks the enzymes from doing their work, resulting in higher—possibly even life-threatening—concentrations of the drug in the bloodstream, or lower concentrations that render the drug ineffective. Interactions can occur even if the grapefruit is consumed hours before the medication.

Grapefruit is not the only citrus fruit that interacts with medications. Consumption of limes, pomelos, and Seville oranges (the kind used in marmalade) should be limited or avoided as well.

Only medications that are taken orally interact with grapefruit. Drugs that are injected, for example, do not. “And even within a class of medications, there are variations,” Reiter says. “In many cases, alternative drugs that don’t react with grapefruit may be available.” If you are partial to grapefruit, she suggests, “ask your doctor if an alternative drug exists.”

Although anyone mixing certain drugs and grapefruit is at risk, the elderly are most at risk for adverse effects, Reiter says, “because they take more drugs.” They also tend to consume more grapefruit products.

If you are not taking any drugs that interact with grapefruit, it can be a part of a healthy diet. But the final word from Reiter: “If you take prescription medicines and grapefruit is a regular part of your diet, consult your health care professional. We try to warn patients,” she says, “but our ‘go to’ counseling point is to just avoid grapefruit. It’s safer that way.”