While alcohol is a common intoxicant involved in DUI arrests and convictions, Arizona law states that a DUI conviction can also result from the influence of drugs, whether illegal or prescription, or a vapor releasing substance that has intoxicating effects. DUI charges may also be issued to someone who is suspected to be under the influence of a combination of substances. Keep in mind that you can still be charged with DUI even if you have a prescription for the substance found in your blood, but there is an affirmative defense to DUI drug charges if you can establish that you are not impaired to the slightest degree.