Illinois law states that a driver is guilty of DUI if he or she operates a motor vehicle while under the influence of alcohol, drugs, or any other intoxicating compound. A person may be found to be under the influence based on a police officer’s observations that the person was acting or driving erratically, slurring speech, or showing signs of confusion. The law also provides that a person is automatically considered to be under the influence for exceeding the statutory limit for blood alcohol content (BAC) or THC concentration.