Between 2008 and 2012, researchers say, new drugs capable of adverse interactions arrived on the market annually, driving the total number of medications now known to have side effects when taken with grapefruit from 17 to 43.
According to David Bailey, a clinical pharmacologist at the Ontario-based Lawson Health Research Institute, grapefruit contains an enzyme called CYP23A4, which can interact with some medications in the gastrointestinal tract, reducing their effectiveness or raising their potency in the blood stream to dangerously high levels.
Drugs affected by the interaction with grapefruit include cholesterol-lowering medications and some that reduce high blood pressure.
Although many drug manufacturers put warnings about interactions with grapefruit on their labels, Bailey says many doctors are not aware of them.
“That’s our big concern," he said, "that this information needs to get out to the practicing clinicians so that they manage use of these drugs properly in their clinical practice.”
All of the drugs that can be affected by grapefruit juice are taken by mouth. Normally, says Bailey, only a small amount of the pills’ active ingredients enters the bloodstream after they’re swallowed. But he says the drug levels can rise dangerously if grapefruit is consumed, because of the interaction with CY23A4 in the stomach.
“This is a normal amount of grapefruit juice, we’re not talking about liters of grapefruit juice here," he says. "But levels can be boosted from the level we want in the body to therapeutic levels that are what we would consider to be high and toxic.”
According to Bailey, the interactions between grapefruit juice and some drugs can cause bleeding in the gastrointestinal tract, respiratory failure and sudden death — even a long time after the fruit or fruit juice is consumed.
Bailey says people should ask their doctor or pharmacists whether it’s OK to consume grapefruit or grapefruit juice with a particular drug.