Drug recognition techniques represent a systematic, standardized evaluation process for detecting observable signs and symptoms of drug use. Indicators include such symptoms as dilated or constricted pupils, abnormal eye movements, elevated or lowered vital signs, and muscle rigidity. Three key elements in the drug recognition process involve verifying that a youth's physical responses deviate from normal, ruling out a nondrug-related cause of deviation, and using diagnostic procedures to determine the category or combination of drugs likely to cause the impairment. Drug recognition techniques consist of 12 steps, each of which must be carefully followed and practiced: drug history, breath alcohol test, divided attention psychophysical tests, medical questions and initial observations, examination for muscle rigidity, examination for injection sites, vital signs examination, darkroom examination, observation of the eyes, statements and observations, evaluator's opinion, and toxicological examination. This 12-step drug recognition process is particularly accurate in identifying the use of central nervous system stimulants and depressants, narcotic analgesics, and PCP.