Every commercial driver license holder must undergo a physical exam by a doctor and receive a medical certificate. Depending on circumstances, it must be repeated every 3, 6, 12 or 24 months. Mine is good for 12 months.
I also have to do a routine drug abuse urinalysis screen and random checks.
I guess it was a medical exam. Three hours of waiting, then six minutes of examination, including emptying my pockets, filling a cup and signing the paperwork.