Bad Medicine
In 1982, seven residents of the Greater Chicago area made an assumption that proved fatal. They all took a dose of Extra Strength Tylenol® that had been laced with potassium cyanide. What they thought was medicine proved to be poison. This crime, still being investigated as of this very week (February 2009), is still unsolved, in spite of the fact that one man went to prison for sending an extortion letter to Johnson & Johnson and is presumed to be the guilty party by many.
Imagine the horror of taking what you thought was beneficial and discovering, too late, that it was killing you!