Let's look at the history of the event. A-Rod denies using any performance enhancing drugs in a TV interview. A while later it comes out that he popped positive on a drug test in 2003. Then he talks on ESPN and claims to be stupid about what he took and what was or wasn't banned. He basically said that everyone was doing it and no one knew what was or wasn't banned. Now he tells us a story about his cousin sending him a substance that he thinks might not of been administered correctly. I don't think we can believe anything he says, seeing as he has a history of lying about what did or didn't happen in the past. We will never know what drug made him test positive, unless the testing company breaks a few laws and releases the results of the drug test.
At this point I'm not sure what to believe or not to believe. How much truth did A-Rod tell us today? No one really knows but him and I'm not sure he even knows the "truth" after years of covering things up.