From my understanding, the drug they have been using is OK if used to the correct frequency and dosage to treat what it has been prescribed for.
Unfortunately it appears that they have used the correct dosage but up to fifty times above the frequency it should have (Instead of twice a year they have used it almost every week of that year). This has treated the ailment but it has also enhanced the performance of the individual above that which is allowed.
Which, in Cycling terms, is the equivalent to a goalkeeper taking 45 seconds to take a goal kick when preserving a 1 goal lead.