Does bureau of vocational rehab drug test?

Depends on which state. Some do, others don't.

You didn't say where you're writing from, but in the US plan on drug testing with any employer, especially if they get support from the government. They'll excuse anything you have a prescription for. If you're violating, AT BEST you won't get the job.

No. But individual employers might drug screen you after you are successfully hired as part of their mandatory requirements for all applicants.

Anybody can improve by drinking coffee, and you wont break the law to do so.