Question: I've been unemployed and job searching the past few weeks. I have a medical marijuana card which I stupidly utilized during this break. Now that I have hit my final interview, I'm a little concerned. I've quit for a while but know it's still in my system.

I know excuses don't matter in the workplace, and a failed UA means you're not getting hired. My question: So I'm flying out of state for this last interview and they mentioned they'll take care of the hr stuff there. Is it possible to have an onsite drug test or will they most likely order one for me in my home state when I return?

Answer: 
I would count on it.

The answer though is it depends on the company you are applying to and the state where you are interviewing. 

My company screens all candidates for certain positions. And none for others. I know for a fact that one of my colleagues has all "real" candidates take drug tests. These people are dealing with multimillion dollar FX contracts and one mess up can be devastating. 

Also there are state laws that add some variance. Some states are more lax on drug testing while others make employers give you a conditional offer before they are allowed to test you. A quick google will give you the state drug info on the state you are going to. 

If this company was giving you a drug test I can't see it happening how you propose - when you get back. No way I have an out of town employee coming in and give him a job offer while he completes drug test back home at some lab I don't know. 

My advice - since you are out of town and since this company isn't in a huge rush. Stop. Think of a good excuse to delay the interview. Get tested at a local lab and don't go until you pass.
It's really up to the employer how they choose to do this. But you can bet that the chances are they will test you in a contracted lab in their area. Are you sure you won't pass? Heavy marijuana use will linger for a while up to 30 days if used very very regularly. If you used it a few times a week, and don't use it currently you might be fine. I suggest testing yourself to see if you pass. You can order a home test at [Drug Tests in Bulk](http://drugtestsinbulk.com/)