Put simply, any chemical substance that, when taken into the body, will impair one's ability to safely operate a vehicle. These are the drugs that impair one's ability to do something, in this case, driving. The DIP drugs are the only categories in which we will see HGN displayed. And again, the presence of VGN without HGN could indicate a serious medical condition. They are also similar in that they produce many of the same effects, such as horizontal gaze nystagmus, vertical gaze nystagmus, slurred speech, and disorientation.
Pupil size remains normal.
Most depressant users ingest these drugs orally. However, a few abusers will inject their drugs intravenously. The injection paraphernailia used by barbiturate abusers are similar to those used by heroin addicts, although a wider gauge hypodermic needle is used because the barbiturate solution is thicker than the heroin solution. The injection sites on the skin of a barbiturate abuser exhibit large swellings and may develop ulcerations resembling large cigarette burns. However, they are not detected by an alcohol breath test and do not produce an odor of an alcoholic beverage.