Sample Collection and Analysis • For caffeine phenotyping, subjects will collect all of their urine for 12 hours after receiving the dose to determine CYP1A2 activity [(AFMU+1X+1U)/17U], NAT-2 [AFMU/(AFMU+1X+1U)], and XO [1U/(1X+1U)]. Urine will be acidified with ascorbic acid (in vitro) to prevent AFMU conversion.