The Hepatitis C virus (HCV) infects over 3% of the world population and is the leading cause of chronic liver disease worldwide. A compound in grapefruit called naringenin was shown to reduce HCV secretion in infected cells by 80%. In addition, it is effective at concentrations that are an order of magnitude below the toxic threshold in human hepatocytes (liver cells) and in mice. Just keep in mind that if you are on medications or herbs that grapefruit can make them much more potent. While that may sound good, it can actually cause overdose at normal doses so be very cautious and inform your healthcare provider if you decide to take therapeutic amounts of grapefruit extract or if you eat them regularly.
 
Hepatology. 2008 May;47(5):1437-45