Here is the breakdown.
If you are in California, you will not have a problem, if you are in another state like Oregon, you might have one.
In a place like Oregon or Montana, you have to prove need through paper trail/medical records prior to your first visit.
In a place like California, you can practically find a Doctor anywhere that will take between 80 and 150$ to hand you a license for no good reason at all. I would not do this myself though. I and friends close to me have had many problems with this, go to a real Doctor, that isn't a pill mill for pot patients. One that actually answers their verification line, and that your local County Health & Safety Services has heard of and worked with. This will help you in the long run. If you want the paper work on your wall to matter, and to stay out of jail and not just get into a Hash Bar, then find a legit Doc. . .
Cheers.