The four signs of impairment are appearance, behavior, speech, and body odor. These four categories form the standard framework used across workplace safety programs, federal transportation regulations, and law enforcement to identify when someone may be impaired by alcohol, drugs, fatigue, or other causes. U.S. Department of Transportation regulations specifically require that any reasonable suspicion determination be based on “specific, contemporaneous, articulable observations concerning the appearance, behavior, speech, or body odors” of the individual.
Appearance
Appearance covers everything you can see by looking at someone: their eyes, skin, clothing, and overall physical state. Bloodshot or watery eyes are among the most commonly noted indicators. Pupils can also signal what type of substance is involved. Stimulants like cocaine and methamphetamine cause pupils to dilate larger than normal, while opioids like heroin and fentanyl cause them to constrict to pinpoints.
Other visible signs include a flushed or unusually pale complexion, extensive sweating or clammy skin, a blank or unfocused stare, jerky eye movements, and a runny or bleeding nose. A general deterioration in grooming or personal hygiene is another red flag, especially when it represents a noticeable change from someone’s normal presentation. Unexplained bruises, disheveled clothing, and visible tremors in the hands also fall under this category.
Behavior
Behavioral signs are changes in how someone acts, reacts, and carries themselves physically. This is often the broadest category and the one that first draws attention. It includes both emotional and physical conduct: irritability, agitation, impulsive decision-making, paranoia, or sudden mood swings that seem out of character. On the opposite end, withdrawal, depression, extreme fatigue, and a lackadaisical attitude toward responsibilities also qualify.
Motor coordination falls here too. Unstable walking, stumbling, poor hand-eye coordination, slow reaction times, and difficulty with basic physical tasks (fumbling with buttons, dropping objects) are all documented behavioral indicators. The Canadian Human Rights Commission flags “working in an unsafe manner or involvement in an incident” as a key warning sign, along with consistent lateness, absenteeism, and reduced productivity.
Federal observation checklists also include fidgeting, irregular breathing, nausea or vomiting, and hand tremors. The core question is whether the person’s conduct has noticeably shifted from their baseline, not whether any single behavior is present in isolation.
Speech
Speech changes can be subtle or obvious, and they go well beyond simple slurring. Official observation forms used by federal transit agencies track a wide range of speech indicators: slurred or slowed speech, loud or boisterous speech, incoherent or nonsensical statements, repetitive or rambling conversation, rapid or pressured talking, excessive talkativeness, and exaggerated enunciation (overcorrecting to sound sober).
Impairment can also affect the content and coherence of what someone says, not just how they sound. Cursing or inappropriate speech, inability to concentrate during a conversation, and delayed responses to simple questions all count. Some impaired individuals speak in short, choppy bursts with long pauses instead of forming complete sentences. Others become monotone or robotic in their delivery. The key detail observers look for is deviation from how the person normally communicates.
Body Odor
This category is straightforward but important. The smell of alcohol on someone’s breath is the most obvious example, but observers are also trained to notice the odor of marijuana or other drugs, as well as secondary indicators like heavy use of breath mints, gum, or mouthwash that might be masking a smell. Unusual body odor from excessive sweating can also be relevant, particularly when combined with other signs.
How These Signs Are Used in Practice
In workplace settings governed by DOT regulations, supervisors must be trained to recognize these four categories before they can initiate a reasonable suspicion drug or alcohol test. The observations must be documented in writing within 24 hours, signed by the supervisor who made them, and recorded before test results are released. This documentation requirement exists to protect both the employer and the employee: it forces the process to be based on observable, describable facts rather than gut feelings or personal bias.
The Federal Transit Administration’s standard observation form breaks these four categories into specific checkboxes. A supervisor checks every indicator they personally witnessed, then writes a narrative summary of the circumstances. No single indicator is enough on its own. The framework works by accumulating multiple observations across the four categories to build a clear picture.
In law enforcement, officers use a related but more structured approach called the Standardized Field Sobriety Test. Research shows this battery of physical tests can correctly classify individuals as sober or impaired 91% of the time at a blood alcohol level of 0.08% or higher. The eye-tracking component (horizontal gaze nystagmus) is the most accurate single test, with a false positive rate of only about 2% among sober subjects. The walk-and-turn test has a higher baseline failure rate of roughly 22% even in sober people, which is why officers are trained to use multiple tests together rather than relying on any one indicator.
Why No Single Sign Is Definitive
Many individual signs of impairment have innocent explanations. Bloodshot eyes can come from allergies. Slurred speech can result from a medical condition called dysarthria, which affects the muscles used for speaking. Unsteady walking might reflect an injury or inner ear problem. Fatigue from a poor night’s sleep can mimic several behavioral indicators.
That’s why the four-category framework exists as a pattern-recognition tool. A person with bloodshot eyes, the smell of alcohol, slurred speech, and unsteady coordination presents a very different picture than someone who simply looks tired. The more categories involved, and the more indicators present within each category, the stronger the overall observation. This layered approach is what makes the system useful across such different settings, from a construction site to a traffic stop to a hospital workplace policy.