The usual case of driving under the influence involves alcohol. The claim by the police or District Attorney is that the driver is not only under the influence but has a blood alcohol level of more than the legal limit of .08 percent. More and more often people are being arrested for driving under the influence of prescription drugs that have nothing to do with alcohol.
Many times a doctor prescribes medication for the patient. The patient is told don't take the medications with alcohol. The patient follows the doctor's orders but still is arrested for being under the influence of drugs while driving. Can the patient/driver be successfully prosecuted for driving under the influence even if the doctor's orders are followed and the patient doesn't intend to drive under the influence? The answer can be, yes. How can this be?
Driving under the influence of drugs is a general intent crime. That means the patient/driver doesn't need to intend to drive while under the influence of drugs, he/she just needs to willfully drive the car after intentionally taking the medication. There isn't any specific intent to drive while under the influence needed.
There are two main methods to successfully defend a driving under the influence of drugs charge. First, the argument should be that the amount of drugs in the patient/driver's system is not over the therapeutic level needed to treat the condition, and at that level the driver is not impaired for the purposes of driving a motor vehicle.
The second line of defense can be that the cause of the symptoms leading to the conclusion that the patient/driver is under the influence is the disease or medical condition and not the medications used to treat the condition. In other words, the symptoms exhibited by the patient/driver are not caused by the medications but by a disease over which the defendant has no control. Many physical maladies have symptoms that appear to the uninformed to be caused by excessive ingestion of drugs, prescribed or not. If expert testimony can be had to refute the officer's claim of DUI but instead be "driving while diseased" a successful defense can be had.