The Food and Drug Administration (FDA) recently ordered Bristol-Myers Squibb Company to place a "black-box" warning on the packaging of its antidepressant drug, Serzone, informing users that the medication may cause liver failure. The order also requires the company to send letters to doctors alerting them of Serzone's dangerous side effects. Serzone's black-box warning is used only for the most serious of side effects.

The FDA estimates that one in 250,000 to 300,000 users of Serzone will suffer liver failure caused by the medication. Canadian health officials issued a Serzone warning last summer after researchers linked the antidepressant to 109 "serious hepatic events."

Analysts predict that the $14.4 billion a year company will suffer heavy losses as doctors often shy away from drugs burdened with a black-box warning. Bristol-Myers has already laid off 3,000 employees.