I wonder if the substance is Clenbuterol? There have been a tremendous number of inadvertent pops on that due to tainted meat. This was the substance that led to Alberto Contador's loss of his Giro and a Tour title when they CAS reversed the Spanish drug agency's exoneration because they could not prove it was from the Cape Verdean meat. On the other hand, half of Mexico's youth soccer team popped but were able to get their suspension revoked.