If there is anything that drives me crazy it's when people presume definitively that they know what another person thinks and knows.
Yes, I would not be surprised if Wes Welker knows exactly what Molly is (though I can tell you that I've never heard of the drug before today). And I would not be surprised if he knows how to get the drug. And I would not be surprised if he knew full well that he was taking the drug that day. But he says he doesn't take drugs, he says he doesn't know about this drug and he says he didn't take it at the derby.
It may be naive of me to think that Wes could be telling the truth, but... Naive may not be correct most of the time, but naive is correct some of the time. In other words, if you don't know for sure, you shouldn't act like you know for sure. As wise and 'in the know' as some people think they are, the truth is often a surprise.