SayNoToDrugs is exactly right! Your criminal record can be viewed while your medical information is always kept confidential.
The HIPAA Privacy Rule regulates the use and disclosure of certain information held by health insurers, and medical service providers. It establishes regulations for the use and disclosure of Protected Health Information (PHI). PHI is any information which concerns health status, provision of health care, or payment for health care that can be linked to an individual. This is interpreted rather broadly and includes any part of an individual's medical record or payment history.
If you don't get the job, at least you can't blame the medical marijuana! (Unless you just didn't use enough before your interview)
Best of luck with your potential new employment!