As millions of Americans consume over-the-counter herbal and botanical supplements in a bid to boost health, there is increasing evidence that these products can interfere with a wide range of prescription medications used to treat everything from cancer to depression to high blood pressure.

Recent studies have found that a greater number of supplements than previously thought may affect the way certain enzymes in the body metabolize drugs. Some supplements may inhibit the enzymes’ ability to break down a drug and clear it from the body, causing medication to build up to potentially toxic levels and even cause overdose. Other supplements may increase the rate at which a drug is broken down, clearing it from the body too quickly to be effective.

Botanicals, for example, can interfere with drug-metabolizing enzymes in the liver, stomach and intestines and proteins in the blood that can alter the way drugs are distributed throughout the body.

Researchers at the University of Minnesota in Minneapolis are exploring interactions between cancer drugs and dietary supplements, based on data extracted from 23 million scientific publications, according to lead author Rui Zhang, a clinical assistant professor in health informatics. In a study published last year by a conference of the American Medical Informatics Association, he says, they identified some that were previously unknown.

For example, the herb Echinacea, often taken in the belief it boosts immunity and wards off colds, is already known to affect the way certain chemotherapy drugs work. But the researchers also identified a possible interaction with a breast cancer drug that could reduce its effectiveness.

Kava, which is used to treat sleep problems and relieve anxiety and stress, can potentially reduce the effectiveness of a breast cancer drug as well. And the researchers found that grape seed extract, which is used for some cardiac conditions, can potentially increase side effects of the cancer drug.

Philip Gregory, an associate professor of pharmacy and director of the Center for Drug Information and Evidence-Based Practice at Creighton University in Omaha, Neb., says many patients who are admitted to intensive care units have supplements circulating in their system that can interact with drugs and cause bleeding, liver, heart and nervous system complications, so it is important to ask about supplements in medical history-taking.

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