A DRE is a police officer specially trained in recognizing specific symptoms and behaviors that are caused by drugs. The officers take over 80 hours of classroom instruction and 100 hours of field certification training, pass several written examinations, conduct at least 15 evaluations, and have 4 separate drug categories confirmed by toxicology. The DRE can determine if the impairment is caused by alcohol, drugs, a combination of both, or a condition that may require medical attention. Urine or blood samples are analyzed for drug type. Symptoms and general characteristics are listed for drugs in categories of central nervous system (CNS) depressants, CNS stimulants, hallucinogens, phencyclidines, narcotic analgesics, inhalants, cannabis in the Drug Recognition process. Polydrug use, null effect, overlapping effect, additive effect, and antagonistic effect are also covered. Through the DRE training, law enforcement has the means to identify drug impaired drivers and collect evidence to prosecute them as well as to apply this training to other areas of police work.