This audio interview with Mark Zeigler is a pretty good. Zeigler is a reporter who's followed a lot of the athletic doping scandals and offers insight into why Merritt might have been taking DHEA. The seemingly most likely scenario is that it helps counter some of the side effects of anabolics. Be forwarned the program is about 50 minutes long but you will know a great deal more about doping in endurance sport if you give it a listen.