Taylor, head of cardiology at Walter Reed Army Medical Center, says the results "cast into doubt" the basic mechanism by which Zetia cuts LDL cholesterol.

FORBES: Vytorin Study Shows No Benefit

Both drugs work by the same basic mechanism as Vioxx, the Merck (nyse: MRK - news - people ) drug that was pulled from the market because it doubled the increase of heart attack and stroke.

FORBES: Pfizer's Tough Sell

Lorcaserin works by the same basic mechanism as Redux, but Arena is betting that Redux's problems were the result of hitting two many other biological receptors in addition to the one that reduces appetite.

FORBES: Obesity Pill Faces Long Wait

Hints that Vioxx might cause heart attacks had existed for years, as basic research pointed to a mechanism by which the drug might cause more clots.

FORBES: Merck's Deleted Data