People in the police and military get drug tested. People in sports get drug tested. People who work in office jobs, construction jobs, supermarket jobs, and every other kind of job get drug tested.
Does the President have to piss in a cup too?
Personally I’m much more concerned about my president being under the influence of drugs than I am about anyone else. The same goes for cabinet-members, senators, congressmen and other people at the upper levels of government.
No cite, but I’m going to go with probably not. Who’s going to make him if he says “No”? Also, while I’ll agree with you that an opium addled commander in chief would be a bad thing, I’m guessing that any presidents choice of stress busting substances would be alcohol if anything. I can’t see his staff allowing the president to puff on a doob when crisis can arise at any moment.
Given the current president’s history, he either stopped using, or was not tested. 
[sub]unproven info, just a joke really[/sub]
The decision on whether or not anyone has to take a drug test is made by either the employer or a governing body (in this case I guess it would be both). The requirements to hold office say nothing about the POTUS being drug-free. Should someone suggest that there be a test, that would be an amendment that would be hard to lobby against.