If an officer suspects drug impairment rather than alcohol, the investigation sometimes includes a mouth swab, also called an oral fluid test, used to screen for the presence of drugs. This is different from a breathalyzer, and it comes with its own set of rules worth understanding.

In many jurisdictions, this kind of roadside screening is voluntary, similar to a preliminary breath test, and you can decline it, though refusal can sometimes be used as part of the overall investigation, similar to declining other roadside tests. Whether it's truly optional depends on your specific state's implied consent laws, which vary.

Officers suspecting drug impairment specifically will often call in a Drug Recognition Expert, a specially trained officer certified through a structured national program to evaluate drug intoxication using a standardized, multi-step process. This isn't an untrained officer improvising. It's a specific, trained role that exists because recognizing drug impairment accurately requires different skills than recognizing alcohol impairment.

If you're ever in a situation where you have a medical condition that could be mistaken for impairment — a panic attack, diabetes-related symptoms, a physical disability — clearly and calmly stating that condition matters, and carrying medical identification can help prevent a genuine medical situation from being misread as intoxication.

Understanding the difference between voluntary roadside screening and a formal, evidentiary test administered at a station changes what you're actually deciding when asked to participate in either one.