How someone acts when they’re high depends entirely on what substance they’ve used. Cannabis makes people slow down and turn inward, stimulants speed them up and push them outward, opioids sedate them into a near-sleep state, and hallucinogens warp their perception of reality. Each substance leaves distinct physical and behavioral fingerprints, and knowing what to look for can help you recognize what’s happening with someone around you.
Cannabis: Slow, Giggly, and Easily Distracted
Cannabis directly affects the parts of the brain responsible for memory, learning, attention, decision-making, coordination, emotions, and reaction time. In practice, that means someone who’s high on cannabis often seems mentally scattered. They lose track of what they were saying mid-sentence, repeat themselves, or laugh at things that aren’t particularly funny. Time feels distorted to them, so five minutes can feel like an hour.
Physically, the most obvious giveaway is red, bloodshot eyes. Cannabis causes blood vessels in the eyes to expand, producing visible redness. Pupils may be dilated or normal-sized. Coordination suffers, so movements can look clumsy or slightly delayed. Most people experience increased appetite (the well-known “munchies”) and may become fixated on food. Their reaction time slows noticeably.
Socially, cannabis tends to make people quieter and more withdrawn, though some become unusually talkative or animated, especially in group settings. At higher doses, anxiety and paranoia can surface. Someone might become suspicious, hypervigilant, or uncomfortable in situations that wouldn’t normally bother them. The overall impression is of someone who’s pleasant but operating on a slight delay.
Stimulants: Wired, Talkative, and Restless
Cocaine, amphetamines, and methamphetamine all ramp up the brain’s dopamine system, producing a surge of energy and confidence. A person on stimulants often talks rapidly and at length, jumping between topics with unusual enthusiasm. They may seem intensely focused on a task or, conversely, unable to sit still. Physical restlessness is one of the clearest signs: pacing, fidgeting, jaw clenching, or repetitive movements like picking at skin or grinding teeth.
Their pupils dilate noticeably. Cocaine causes this by blocking the reuptake of a stress hormone that controls pupil size, and amphetamines produce the same effect through a similar mechanism. Heart rate and body temperature rise. The person may sweat even in a cool room and seem unnaturally alert or “amped up.”
At moderate doses, someone on stimulants can seem charismatic, overly confident, and unusually productive. At higher doses or after prolonged use, the picture shifts. Agitation, anxiety, and paranoia become common. Methamphetamine in particular can produce agitated paranoia, where the person believes others are watching them or plotting against them. They may check windows repeatedly, whisper, or become hostile if they feel challenged. Sleep deprivation from extended use intensifies these effects dramatically.
Opioids: Drowsy, Slow, and Nodding Off
Opioids, including heroin, fentanyl, and prescription painkillers, produce the opposite picture from stimulants. The hallmark behavior is “nodding,” where the person drifts in and out of consciousness, sometimes mid-conversation or even while standing. Their head droops, eyes close, they briefly startle awake, then drift off again.
The physical signs are distinctive. Pupils constrict to tiny pinpoints, even in dim lighting. This effect starts within 15 to 60 minutes of use and lasts roughly 3 to 5 hours. Speech slows and slurs. Movements become heavy and uncoordinated. Nausea and vomiting are common, especially in people with less tolerance. The person may seem confused, unaware of their surroundings, or respond to questions with a noticeable delay.
Someone on opioids typically appears calm or even blissful in the early stages of intoxication. They may describe feeling warm, content, and free of worry. But the line between “high” and “dangerously intoxicated” is thin. The classic triad of opioid poisoning is extremely small pupils, depressed breathing, and reduced consciousness. If someone who appears to be on opioids becomes unresponsive, their breathing becomes slow or irregular, or their lips turn blue, that’s a medical emergency.
Hallucinogens: Altered Perception and Emotional Swings
LSD, psilocybin mushrooms, and similar substances reshape how someone perceives the world around them. The person may stare at ordinary objects with fascination, describe seeing patterns or colors that aren’t there, or experience synesthesia, where senses blend together so that they “see” music or “hear” colors. Sensations feel amplified. Textures, sounds, and lights may seem overwhelming or deeply meaningful.
Emotionally, someone on hallucinogens can swing between euphoria and distress quickly. Periods of intense psychological effects often alternate with moments of relative clarity. Most people experience enhanced empathy and a feeling of connection, but anxiety, apprehensiveness, and panic can surface, especially at higher doses or in uncomfortable environments. True hallucinations and delusions do occur but are actually rare with classic hallucinogens like LSD.
Pupils dilate significantly. The person may seem detached from their body or describe feeling like they or the world around them isn’t real. Conversation can become abstract, philosophical, or difficult to follow. They may laugh or cry without an obvious trigger. Physically, coordination is mildly impaired, but nothing like the sedation seen with opioids or the clumsiness of alcohol.
How Eyes Tell the Story
Pupil size is one of the most reliable quick indicators of what substance someone has used. Stimulants like cocaine and methamphetamine dilate the pupils because they increase levels of stress hormones that control the muscles in the iris. Hallucinogens also cause significant dilation. Cannabis can produce mild dilation along with its signature redness.
Opioids are the major exception. They constrict pupils to pinpoints by stimulating a specific area of the brain that controls pupil size. This constriction is so consistent that it’s considered a diagnostic marker. If someone is very drowsy with tiny pupils, opioids are the most likely explanation.
Depressants like barbiturates and benzodiazepines generally leave pupil size normal, though other eye-related signs like involuntary eye movements or difficulty focusing may be present.
Memory and Speech Changes
Across nearly all substances, short-term memory takes a hit. Someone who’s high may forget what they were saying, repeat stories, miss details you just told them, or struggle to recall recent events. With cannabis, this is especially pronounced: the person might ask the same question twice within minutes.
Speech changes vary by substance. Opioids and depressants slow speech and cause slurring. Stimulants speed it up, sometimes to the point where the person is hard to follow. Hallucinogens can make someone’s speech disjointed or tangential, as if they’re narrating an internal experience that doesn’t connect to the conversation. Difficulty finding the right words and increased pauses before responding are common across multiple drug types.
When Something Goes Wrong
Most intoxication resolves on its own, but certain signs indicate a dangerous situation. Loss of consciousness or being unable to wake someone is always serious. Seizures, breathing that becomes very slow or stops, blue-tinged lips or skin, and persistent vomiting while unresponsive all require emergency help immediately.
With stimulants, extreme agitation, very high body temperature, and chest pain signal potential overdose. With opioids, the danger is respiratory depression, where breathing slows so much the brain doesn’t get enough oxygen. With hallucinogens, the primary risk is psychological: severe panic, dangerous behavior driven by delusions, or self-harm during an intense episode. In any of these cases, calling 911 is the right move.