Grapefruit juice may increase medication potency

Nutrition Health Review, Wntr, 1996

Most of us don't pay much attention to what we drink when we take our medications, but doctors at the University of Michigan Medical Center (U-M) suggest that perhaps we should.

The U-M is leading a race to determine why normal, everyday grapefruit juice dramatically increases the body's ability to absorb some commonly prescribed medications, including certain blood pressure drugs.

"For many medications that are taken orally in pill form, the majority of the-drug is not absorbed from the digestive tract but instead passes out of the body and is, in effect, wasted," said Paul B. Watkins, M.D., director of the U-M General Clinical Research Center. "With some medications, however, when you take them with grapefruit juice, much more of the drug gets into the body and, hence, much less is wasted."

According to Watkins, the grapefruit's effect on medications is fueled by its ability to override an enzyme in the intestine that normally regulates the absorption of drugs into the body.

He noted that researchers at the university are collaborating with the U.S. Food and Drug Administration (FDA) to uncover the specific compound or compounds within grapefruit that causes increased absorption.

"There are really two important reasons for detecting the compound in the grapefruit that's causing this effect," Watkins said. "First, pinpointing the compound should lead to better drugs that will have less waste; that is, less drug will be unabsorbed and passed from the body.

"Second, people absorb varying amounts of many medications. Some people might absorb only one tenth of a pill, and others might absorb five times more," Watkins continued. "For some of these drugs, grapefruit juice tends to reduce these differences through its ability to override the intestinal enzyme that inhibits absorption. This can make drug absorption more consistent and predictable."