“Why did the US Food and Drug Administration (FDA) allow the experimental blood substitutes to be tested in humans despite knowing the products significantly increased the risks of heart attacks and death?,” questioned an NIH study, published online yesterday by the Journal of the American Medical Association (JAMA).

According to the study, the Food and Drug Administration approved experiments with artificial blood substitutes even after studies showed that the controversial products posed a clear risk of causing heart attacks and death. The federal agency was aware of the increased health risks as early as 2000 but did not make the data available to the public.

The researchers from the National Institutes of Health reviewed the data from more than 3,711 patients who participated in 16 studies testing five different types of artificial blood, and found that the products nearly tripled the risk of heart attacks and boosted the chances of dying by 30 percent.

The study found that overall patients given blood substitutes faced a 30 percent greater risk of death and a 171 percent increased risk of heart attack compared to those who received conventional treatment.

The authors, from the National Institutes of Health and the consumer group Public Citizen, criticized the FDA for not putting a stop to further experiments. They questioned why the FDA allowed additional testing of the products to go forward and why the agency is considering letting yet another study proceed.

Charles Natanson, a senior investigator at the National Institutes of Health who led the study, said, "It's hard to understand. They already had data that these products could cause heart attacks and evidence that they could kill."