A drug recognition expert has specific training in the indicia of drugs as well as psychophysical tests and clinical indicators. Roadside, the person has been stopped for some reason. They are put through divided attention tests, the standardized field sobriety test battery. That will show if the person is impaired by something. If it's suspected to be alcohol, they get a breath demand, and then go back for a breath test. If it's suspected to be drugs or something other than alcohol, we ask that they go back and participate in a drug evaluation.
The first part of the drug evaluation is to obtain a breath sample to rule out alcohol as the primary cause of impairment. If the level is over the legal limit, then they are charged with driving while over 80 milligrams percent. If alcohol is ruled out, they then go through the same sobriety test they did at roadside, plus two others, in a controlled environment where there are no distractions from oncoming traffic, no distractions from bystanders, where the surface is level, and where there are no weather conditions to be concerned about either.
At the conclusion of that, we can prove that the person is either impaired or not. We still don't know what is causing the impairment. That's where we use the clinical indicators. We'll take the person's pulse on three separate occasions. We'll take their blood pressure and their body temperature, check their muscle tone, and look at their pupils in three lighting conditions—regular room light, near total darkness, and direct light. In doing this, we want to see what size the pupils are and how they react to the light. We will also check to ensure that the person doesn't have any medical problems.
At the conclusion of the clinical portion, we can put the person in one or more of seven drug categories--we're not looking for a specific drug, just the broad category—or rule that out if the problem is medical or fatigue. At this point, we're going to interview the driver, tell them what we suspect they're using, and at the conclusion of the interview ask them for a bodily fluid sample to be sent to a lab for analysis to confirm or refute what the evaluator has called.