Any drug that will impair a driver's ability to drive safely should not be taken by a commercial driver. Controlled substances or prescription medications without a prescription from a licensed practitioner are prohibited. If a driver uses a drug identified in 21 CFR 1308.11 (391.42(b)(12)) or any other substance such as amphetamine, a narcotic, or any other habit forming drug, the driver is unqualified.
There is an exception: The prescribing doctor can write that the driver is safe to be a commercial driver while taking the medication. In this case, the Medical Examiner may, but does not have to certify the driver. Please be aware, that if a Medical Examiner does not feel comfortable to certify you despite the prescriber stating you are safe, they are not required to do so.

Any anti-seizure medication used for the prevention of seizures is disqualifying.
Methadone use is disqualifying.