A doctor dragged off an overbooked United Airlines flight has been in trouble before.

FOX's Rachel Sutherland reports from Washington:

Dr. David Dao, a pulmonologist from Kentucky, was convicted of drug-related offenses in 2004 and surrendered his medical license.

The "Courier Journal" reports Dr. Dao was involved in fraudulent prescriptions and was sexually involved with a patient. HeĀ served five years probation and then in 2015, he started practicing medicine again under conditions set by the Kentucky Board of Medical Licensure.

The 69-year-old is seen on a viral video...

Being forcibly removed from theĀ United flight. The Transportation Department is investigating the incident.

In Washington, Rachel Sutherland, FOX News.

Follow Rachel Sutherland on Twitter: @SutherlandFOX