I'm sure some do it, but most doctors I know take their jobs very seriously and wouldn't even consider risking the remote chance of being caught. It would not only end their career permanently, but it would ruin their life as they would get jail time and it would be all over the news. The risk far outweighs the benefit. It takes at least 12 years and hundreds of thousands of dollars to become a doctor. It also takes an incredible amount of determination, skill, drive and perseverance. Most of the people who make it to the end are the polar opposite of the type of people who typically exhibit drug seeking behavior. They are typically very satisfied with their quality of life, and let's face it...the majority of hard drug users take drugs to escape from life problems. Like I said, I'm sure there are plenty of doctors who do, just as there is corruption in almost any profession, but I think it's more of a rare exception.
i don't have statistics but i think drug abuse is actually more common among doctors than a lot of other professions. reasons for this could be the stress of working as a doctor, combined with the access to and knowledge of how to use various drugs.