Prescription drugs and alcohol usually do not mix well. This should be common knowledge. But drunk driving defendants often claim that their impairment at the time of arrest was due to consuming only a small amount of alcohol while having prescribed drugs in their system.
Whether truthful or not, this defense isn’t viable in Massachusetts.
According to the Appeals Court in Commonwealth v. Bishop,
where the defendant is accused of operating a motor vehicle while under the influence of alcohol, and there is evidence both of the voluntary use of alcohol and of prescription medicine, taken as prescribed, the jury should be instructed…that the defendant is charged with operating while under the influence of intoxicating liquor and other substances…In order to find guilt, the jury need only to find that the liquor contributed to the defendant’s impairment. (Citations and quotations omitted.)
Only when the driver’s impairment is due solely to prescribed drug use can a defense be raised. Again, quoting the Appeals Court in Bishop:
the jury also should be given…a Wallace instruction, specifically, that the defendant is entitled to an acquittal if her intoxication was caused solely by her prescription medication, taken as prescribed, and she did not know or have reason to know of the possible effects of the drug on [her] driving abilities. (Citations and quotations omitted.)
To my knowledge, there is no case law on involuntary intoxication with drug use that is not prescribed.