The drug works by tripping a cellular switch that was discovered serendipitously by scientists studying an unrelated drug--Rapamune, a Wyeth chemical used to suppress the immune systems of organ transplant patients.
Most nations have instead adopted highly regulated donation systems like the United Network of Organ Sharing in the U.S. UNOS monitors each kidney, lung, heart or liver available from a deceased donor going to a patient on a wait list.
The UK government questioned whether an opt-out organ scheme was desirable, "feasible", or whether it was necessary to run two different systems, arguing it would lead to confusion.