Allopurinol is a treatment of high uric acid levels, often used in treatments of gout; therefore, the number of people suffering its side effects increases rapidly, ranking as No.1 for medical compensate in Taiwan in 2006.Research done around the world shows that the Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) caused by Allopurinol has much to do with the PG5801 gene. Asians with the PG5801 gene have 700 times more risk of SJS/TEN when taking Allopurinol than those who don’t have the gene.