definitely don't ask at the interview.

if it's a more upscale job, you can ask if their medical benefits cover an annual physical exams and blood/urine checks.

another thing is to ask them if they need a doctor to sign off that you have no medical conditions, psychiatric issues, or drug problems that would limit your work when you're coming in as a new employee.

i did the second one for my last job, and it went over fine.

their response might also depend on the 'vibe' you give them, what job its for, and whether or not the manager/boss is an a-hole

definitely don't ask about it at the interview