According to this NY Times article, Doug O'Neill, the trainer of this year's Kentucky Derby winner, I'll Have Another, has been sanctioned 12 times in the last 14 years for doping his horses.
But the problem is bigger than that. Takeaway quote:
The racing industry has come to realize that lax regulation and the absence of meaningful punishment have fostered a culture where top trainers with multiple drug violations are more the rule than the exception. Of the top 20 trainers in the United States — measured by purses won in 2011 — only two, Christophe Clement and Graham Motion, were never cited for a medication violation, according to the Racing Commission International database.Enjoy the Preakness.