You people do realize that there is no one steroid pill or injection right? There is a list of banned chemicals. Silly example but, you could eat a burger with HGH injected into it and be banned.
It's not only plausible but likely that he took something that had a banned chemical in it.
Also for the person that said he's rare you are over-rating Merriman. They are lots of player that are his size and athleticism range.
The difference is that Merriman plays to try to hurt people so he's more intense when he gets in on a play.