It is a crime to operate a motor vehicle while under the influence of alcohol or drugs, regardless if it is prescription medication or illegal substances.  Field sobriety tests may be preformed if there is reason to believe the driver is drunk.  If the BAC (Blood Alcohol Content) of the driver exceeds the legal maximim for the state, they are considered intoxicated and charged with a DWI (Driving While Intoxicated).  If the driver seems severely impaired or are percieved as a threat to the safety of other drivers, they may be pulled over for driving recklessly.  If the officer has probable cause, he is legally permitted to search the vehicle for drugs or alcohol.  If he observes the driver exhibiting behaviors consistant with a person under the influence, he may administer a field sobriety test.  If the driver should fail, or drugs are found in his or her posession, they are arrested immediately.