What term describes a situation where neither drug induces signs of impairment, such as horizontal gaze nystagmus?

The term that describes a situation where neither drug induces signs of impairment, such as horizontal gaze nystagmus, is "null." This term signifies that in the context of drug interactions, the effects of the drugs do not lead to any observable impairment.

In the context of law enforcement and drug evaluations, identifying clear signs of impairment is essential for accurate assessments. A null interaction implies that the combination or presence of these specific drugs does not produce detectable impairment effects, indicating that the individual may be less likely to exhibit behaviors associated with intoxication.

Other terms like "overlapping," "additive," or "psychotropic" do not accurately convey the lack of impairment in this context. "Overlapping" might suggest some shared effects, while "additive" indicates that effects could combine to produce greater impairment. "Psychotropic" simply refers to substances that affect mental state without specifying anything about their impairment effects when used alone or in combination. Therefore, "null" is the most appropriate term to describe the absence of impairment signs when neither drug shows effects such as horizontal gaze nystagmus.