"Fellows [an Arizona Highway Patrol Officer] will talk to the arresting officer, then to the suspect driver. A drug recognition expert will rule out head injuries if the driver is involved in an accident, or any mental health issues. Their job is to recognize drug behavior, determining when the last time the driver used drugs and the kind of drugs they used.
The DRE officer interviews the suspect, asking their age, when the last time they slept was, what they ate and any physical effects. The expert will perform eye tests, looking for horizontal or vertical reflexes.
They will also look into a suspect's nose or throat to look for signs of drug use and check the pulse rate and blood pressure, as well as check for needle marks on the suspect's arms.
Fellows determines which drugs the suspect has taken based on seven categories, including depressants, stimulants, hallucinogens, narcotics, cannabis, inhalants and dissociative anesthetics."
We've been noticing an increase in the amount of reported stories about abusing inhalants while driving, so it's commendable that the issue is becoming more recognized.