Many people who today choose herbal products in lieu of prescription medications assume that because these products are natural, they must be safe, even when the evidence for this assertion is essentially anecdotal. Recent studies have shown that herbals are highly variable in quality and composition, with many marketed products containing little of the intended ingredients and containing unintended contaminants, such as heavy metals and prescription drugs. A few herbals are banned outright in several countries. Comfrey and kava have been associated with liver failure, aristolochia with genitourinary cancer (De Smet 2002), and ephedra with heart attacks and strokes (Shekelle and others 2003). More important, herbals contain ingredients that can accelerate or.
