FDA officials say Aranesp, Epogen, and Procrit will now carry "black-box" warnings alerting patients and doctors to lessen the risk of blood clots by using the lowest dose of medication needed to avoid the need for blood transfusion. The new boxed warning also includes information that they can increase risk for death or serious medical complication if used too aggressively in some patients.

The agency is also telling researchers to consider ending clinical trials involving the drugs.

Aranesp, Epogen, and Procrit are in a class of drugs called erythropoiesis-stimulating agents (ESAs) used to stimulate the production of red blood cells. The drugs are widely used in patients with chronic kidney failure (such as those with end-stage renal disease who require dialysis) and patients undergoing cancer treatments.

"Recent reports of studies with erythropoiesis-stimulating agents (ESAs) have shown a higher chance of serious and life-threatening side effects and greater number of deaths in patients treated with these agents," an FDA public health advisory says.