According to a Food and Drug Administration (FDA) study, physicians largely ignored FDA recommendations advising them to monitor liver enzymes in their patients taking Rezulin. In addition, it appears that doctors also dismissed liver damage advisories issued by Rezulin's manufacturer, Warner-Lambert Pharmaceuticals. By the time Rezulin was withdrawn from the market in early 2000, hundreds of people had experienced liver failure.

Despite the FDA's intervention, no meaningful liver toxicity monitoring occurred. Prior to direct mailings to physicians, liver enzyme testing was conducted in fewer than 15% of patients taking Rezulin. Following the mailings, testing did increase, but only by 30%.

The minimal increase in testing leaves FDA officials speculating whether doctors pay any attention to advisories issued by the agency.