Which substance can potentially cause horizontal gaze nystagmus?

Alcohol is known to cause horizontal gaze nystagmus (HGN), which is a condition characterized by an involuntary jerking of the eyes as they gaze to the side. When an individual is under the influence of alcohol, it can affect the functioning of the nervous system, impairing the ability of the eyes to smoothly track a moving object. This impairment results in the characteristic nystagmus, which is a critical indicator used in standardized field sobriety testing to determine a driver's level of intoxication.

While caffeine, nicotine, and Tylenol can have various effects on the body, they are not associated with causing horizontal gaze nystagmus in the same way that alcohol does. Caffeine is a stimulant that can lead to increased alertness or jitteriness but does not affect eye movement to the degree that causes HGN. Nicotine may have other physiological effects, but it does not produce the specific eye movement abnormalities typically observed with alcohol intoxication. Tylenol, being an analgesic, is not related to this eye movement phenomenon at all. The recognition of HGN is a key tool for law enforcement agencies during roadside evaluations to assess possible intoxication levels.