You cannot take a controlled substance or prescription medication without a prescription from a licensed practitioner. You are not qualified if using a controlled substance identified in 21 CFR 1308.11 (Code Of Federal Regulations) Schedule I, an amphetamine, a narcotic, or any other habit-forming drug. There is an exception: The prescribing doctor can write that you are able to safely operate a commercial vehicle while taking the medication. In this case, the medical examiner may, but does not have to, certify the driver. Note: Any medication used for the prevention of seizures is disqualifying.