How to Describe Someone Under the Influence of Drugs

Describing someone under the influence of drugs accurately means identifying a cluster of observable signs rather than relying on a single telltale clue. The eyes, speech, coordination, breathing, and behavior all shift in ways that depend heavily on which substance is involved. A person on a stimulant looks and acts almost nothing like a person on an opioid, and both look different from someone who has smoked cannabis. Getting the description right matters whether you are writing a medical report, documenting a workplace incident, crafting a realistic scene in fiction, or simply trying to help someone you are worried about.

Start With the Eyes

If you could pick only one body part to describe, the eyes give you the most information. Pupil size alone can narrow things down considerably. Opioids shrink the pupils to pinpoints, even in dim lighting. Stimulants like cocaine and methamphetamine blow them wide open. Cannabis tends to cause dilated pupils with a sluggish reaction when light hits them. Hallucinogens also dilate the pupils, sometimes dramatically. These changes happen because different drugs act on the autonomic nervous system in opposite directions, and the pupils respond almost involuntarily.

Beyond pupil size, the way someone’s eyes track movement matters. Involuntary jerking of the eyes, called nystagmus, is a hallmark of certain drug classes. In a study of PCP intoxication cases, horizontal nystagmus showed up in about two-thirds of patients, and vertical nystagmus in nearly half.¹ Alcohol and sedatives can also trigger horizontal nystagmus, but vertical nystagmus is much more suggestive of dissociative drugs like PCP or ketamine. If someone’s eyes are bouncing up and down when they try to look straight ahead, that is a strong and specific indicator.

The condition of the eyelids and the whites of the eyes adds another layer. Cannabis is famous for producing bloodshot eyes and a heavy-lidded, droopy appearance. A forensic study of drivers with THC in their system found that red eyes were present in about 94% of cases, and droopy eyelids in roughly 86%.² The redness, known clinically as conjunctival injection, correlated with blood THC levels and was one of the few physical signs that reliably pointed to cannabis influence.³ So when describing a cannabis-influenced person, the combination of red, glassy, half-closed eyes with dilated pupils that react slowly to light is about as textbook as it gets.

Pupil size, pupil reaction to light, the ability of the eyes to converge on a near object, and nystagmus are all considered useful indicators of the type of drug someone has been exposed to.⁴ In practice, the eyes are the first place trained evaluators look, and the last place that a drug’s effects can be hidden.

How Different Drug Classes Present

Drugs roughly sort into categories that produce distinct profiles. The person’s overall appearance, energy level, and physiology tend to follow the drug class, and accurate description depends on recognizing these patterns rather than guessing at a specific substance.

Stimulants: Cocaine, methamphetamine, and amphetamines produce dilated pupils, elevated heart rate and blood pressure, rapid or pressured speech, restlessness, and sometimes sweating or jaw clenching. The person may appear hyperalert, fidgety, and unable to stay still. Body temperature can rise. In high doses, agitation may cross into paranoia or aggression.
Opioids: Heroin, fentanyl, and prescription painkillers produce constricted (“pinpoint”) pupils, drowsiness or nodding off, slowed speech, and a relaxed or limp posture. The most dangerous sign is slowed breathing. Opioids reduce the respiratory rate through their action on brain regions that control involuntary breathing, and in severe cases both breathing rate and oxygen levels drop together.⁵ The mechanism is a direct suppression of the brain’s breathing-rhythm generator, which slows the rate of breathing more than it reduces the depth of each breath.⁶ If someone is barely conscious with tiny pupils and breathing only a few times per minute, that picture is almost diagnostic.
Sedatives and depressants: Benzodiazepines, barbiturates, and similar drugs produce effects that overlap with alcohol: slurred speech, poor coordination, unsteady gait, and drowsiness. Pupils may be normal or slightly dilated. On balance and walking tests, people under the influence of depressants tend to sway, struggle to touch heel-to-toe, and have difficulty following multi-step instructions.⁷
Hallucinogens and dissociatives: LSD, psilocybin, PCP, and ketamine produce dilated pupils, altered perception of time and space, and sometimes disorganized or bizarre speech. PCP specifically can produce a combination of nystagmus, high blood pressure, agitation, and a strange indifference to pain. In a case series, agitation was reported in nearly 39% of PCP-intoxicated patients, and about a quarter had retrograde amnesia.¹

These profiles overlap in places. A stimulant user and a hallucinogen user can both have dilated pupils and elevated blood pressure. A sedative user and an opioid user can both appear drowsy and uncoordinated. That is why a cluster of signs matters more than any single observation.

Cannabis Deserves Its Own Description

Cannabis does not fit neatly into the stimulant-depressant-hallucinogen framework, and its observable effects are distinct enough to warrant separate attention. Alongside the red eyes and droopy lids described earlier, affected speech was found in nearly 88% of THC-positive drivers in one large study, and a white or greenish coating on the tongue appeared in over 96%.² The smell of marijuana on the person’s clothes or breath, while not a physical sign in the medical sense, was noted in over 82% of those same cases. So a full description of someone who has recently smoked cannabis might include bloodshot, half-open eyes; slow, slightly tangential speech; a coated tongue; a distinct herbal smell; and a general demeanor that is relaxed to the point of seeming detached.

One wrinkle is tolerance. People who use cannabis heavily can look surprisingly normal on standard coordination tests. Research has shown that the standard balance and walking tests used in roadside evaluations are only mildly sensitive to THC in heavy users, likely because frequent exposure builds behavioral tolerance to impairment.⁸ Add even a small amount of alcohol, though, and performance drops sharply. The physical eye signs remain present regardless of tolerance, which is why they are more reliable than behavioral tests for cannabis.

What Trained Evaluators Actually Look For

Law enforcement and clinical professionals who specialize in drug-influence assessment use a standardized set of observations rather than gut feelings. The most structured version of this is the Drug Evaluation and Classification (DEC) protocol, performed by trained Drug Recognition Experts. Research into what makes these evaluations work has identified a core set of clinical indicators that meaningfully predict which drug class a person has used. These include the condition of the eyes and eyelids, the ability of the eyes to converge, pupil size in the dark, how the pupils react to light and whether they show “rebound dilation” afterward, pulse rate, blood pressure, the presence of injection sites, muscle tone, and performance on balance and walking tests.⁹ A separate analysis of the same protocol identified a similar list of nine indicators that significantly predicted the drug category, including a subtle rhythmic flickering of the pupils known as hippus.¹⁰

The takeaway for anyone trying to describe drug influence is that professionals rely on a combination of vital signs (pulse, blood pressure), eye signs (pupil size, reaction, nystagmus, convergence), coordination (balance, walking), and physical evidence (injection marks, muscle rigidity or flaccidity, skin condition). No single finding clinches it. When you see multiple signs pointing to the same drug class, that is when a description becomes credible.

Balance and Coordination Tests and Their Limits

The Standardized Field Sobriety Tests, originally designed for alcohol, are sometimes applied to drug intoxication. They include following a moving object with the eyes (horizontal gaze nystagmus), standing on one leg, and walking in a straight line heel-to-toe. Research has found that all drug categories are associated with impaired performance on at least some of these tasks. People under the influence of depressants and opioids showed the broadest range of failures: swaying while balancing, using arms to steady themselves, putting a raised foot down prematurely, losing balance during instructions, and missing heel-to-toe steps.⁷

These tests have real limitations when it comes to drugs other than alcohol, however. Researchers have pointed out that in the absence of other evidence like physiological signs or observed driving impairment, the standard balance and walking tests have limited ability to identify drug consumption on their own.¹¹ Someone who is high on a stimulant, for example, might pass a balance test while still having dramatically dilated pupils and a dangerously elevated heart rate. The lesson is that describing behavioral impairment alone often misses the picture; you also need to notice physiological signs.

Inhalants Leave Their Own Traces

Inhalants, substances like paint thinner, aerosol sprays, or nitrous oxide that are breathed in for their psychoactive effects, produce a set of signs that are physically different from most other drugs. The intoxication itself can look like alcohol impairment: slurred speech, dizziness, disorientation, and unsteadiness. But inhalants leave unique physical traces. A chemical smell on the breath or clothing is one of the most immediate giveaways. Paint or metallic residue may be visible on the face, around the nose and mouth, or on the hands. Chronic use often produces a characteristic skin irritation around the mouth and nose, sometimes called “huffer’s rash,” where the skin dries out, cracks, and becomes infected.¹² If you are describing someone suspected of inhalant use, these physical clues are often more telling than any behavioral observation.

Synthetic Cannabinoids and Unpredictable Presentations

Synthetic cannabinoids, sometimes sold under names like “Spice” or “K2,” deserve a separate note because they often produce effects that look nothing like natural cannabis. While someone who has smoked marijuana tends to be calm, slow, and red-eyed, someone who has consumed a synthetic cannabinoid can present with a rapid heart rate, agitation, hallucinations, high blood pressure, vomiting, and in more severe cases, seizures or acute psychosis.¹³ The presentation can look more like stimulant toxicity or even PCP intoxication than like a typical cannabis high. This is one reason why describing someone as “acting like they’re on drugs” without specifying what kind of drugs can be misleading. The category matters.

When Drug Influence Mimics a Psychiatric Crisis

One of the trickiest situations for any observer is distinguishing drug-induced psychosis from a psychiatric emergency that has nothing to do with substances. Both can involve paranoia, disorganized thinking, hallucinations, and bizarre behavior. Research into this distinction has found that substance-induced psychosis tends to produce more visual hallucinations and lower overall symptom severity compared to primary psychotic disorders, and that a history of substance dependence is (unsurprisingly) more common in the substance-induced group.¹⁴

For someone trying to describe what they are seeing, this means paying attention to whether the person reports seeing things that are not there (as opposed to hearing things, which is more common in primary psychosis). The presence of other physical signs, like dilated pupils, sweating, elevated heart rate, or nystagmus, can also point toward a substance cause. A person in a psychiatric crisis without drugs on board typically has normal vital signs and normal-looking pupils. When the body is telling one story and the behavior is telling another, drug influence becomes more likely.

Describing the Comedown and Withdrawal

Not everything you observe happens during active intoxication. Someone in the early stages of withdrawal from a substance can look just as impaired, but the signs run in the opposite direction. Methamphetamine withdrawal, for instance, follows a predictable two-phase pattern. In the acute phase, which peaks within the first 24 hours and lasts roughly a week, the person sleeps excessively, eats more than usual, and displays a cluster of depression-related symptoms along with anxiety and drug cravings. Overall severity drops in a fairly linear pattern over that week. After that, a subacute phase follows for at least two more weeks, during which most symptoms stay low but stable.¹⁵

This matters for description because the person in withdrawal looks profoundly different from the person who is high. A methamphetamine user in withdrawal is exhausted, flat, possibly tearful, and sleeping long hours. That is the opposite of the wired, hyperalert, sweaty person you would see during active use. Describing someone as “under the influence” when they are actually in withdrawal is a common mistake, and it leads to very different conclusions about what help they need.

Putting a Description Together

When you actually sit down to describe someone you believe is under the influence, specificity beats vagueness every time. “He seemed out of it” tells no one anything useful. A more informative description layers observable details: “His pupils were barely visible even in the dim room, his speech was slow and slurred, he kept nodding off mid-sentence, and his breathing was shallow and infrequent.” That description points clearly to opioids. Contrast it with: “Her eyes were wide and bloodshot, she was talking rapidly and jumping between topics, her jaw was clenching rhythmically, and she was sweating despite it being cool outside.” That points toward a stimulant.

Good descriptions move through the body systematically. Start with the eyes (pupil size, redness, nystagmus, lid droop). Move to speech (fast or slow, coherent or disorganized, slurred or pressured). Note coordination and posture (steady or unsteady, rigid or limp, restless or lethargic). Include vital signs if you have access to them (fast or slow pulse, high or low blood pressure, breathing rate). And note any physical evidence: smell, residue, injection marks, rash, or unusual skin appearance.

Accurate description is not the same as diagnosis. You do not need to identify the exact substance to produce a useful account. What you need is enough concrete detail that someone reading or hearing your description can form their own picture. The more specific and sensory your language, the closer that picture will be to reality.

Why “Glassy Eyes” Is Not Enough

Everyday descriptions of drug-impaired people tend to rely on a handful of clichés: glassy eyes, slurred speech, erratic behavior. These are not wrong, but they are so nonspecific that they could describe someone who is tired, sick, grieving, or having a blood sugar crash. The forensic literature consistently shows that the indicators that actually predict drug influence are more granular than everyday language tends to capture. Rebound dilation of the pupil, for instance, is not something most people would think to mention, but it showed up as a significant clinical predictor in evaluations of suspected impaired drivers.⁹ The same goes for the inability of the eyes to converge on a close object, or for abnormal muscle tone that makes a person’s arms feel rigid or unusually floppy when moved.

If you are writing for a medical chart, a legal report, or a scene in a novel that you want to feel real, push past the generic. The person’s tongue had a thick white coating. Their eyelids drooped so far the iris was half-covered. When asked to follow a pen with their eyes, the eyes jerked rather than tracking smoothly. Their arm, when lifted, stayed there for a moment before dropping like dead weight. These are the kinds of observations that separate a credible account from a guess.