Zetia lowers cholesterol by blocking the digestive system from absorbing the cholesterol in food. Vytorin combines Zetia with the statin Zocor, which lowers cholesterol levels by blocking the production of an enzyme that the body uses in making its own cholesterol. The theory behind Vytorin was that attacking cholesterol on two fronts, so to speak, would be more effective in lowering cholesterol levels and preventing heart disease.
But the 2008 publication of a study by Merck and Schering-Plough cast doubt on the drugs' efficacy. The "ENHANCE" study showed that the combination drug Vytorin was actually slightly worse than Zocor alone at preventing heart disease. The companies' two-year delay in releasing these results fueled the criticism, and the lawsuits.
Many of the settled suits also raise safety concerns about Vytorin, the result of a separate study that suggested a possible link between Vytorin and cancer.
Both Vytorin and Zetia remain on the market, and although they took a big sales hit when the ENHANCE results were first publicized, the FDA has since reviewed the ENHANCE data and reaffirmed its approval of both Zetia and Vytorin. The FDA take: "Based on current available data, patients should not stop taking Vytorin or other cholesterol lowering medications and should talk to their doctor if they have any questions about Vytorin, Zetia, or the ENHANCE trial."