The signs that someone is high depend on what substance they’ve used, but most fall into a few recognizable categories: changes in the eyes, shifts in mood or behavior, altered speech and movement, and unusual vital signs like a racing or sluggish pulse. Some signs are subtle, others are obvious, and a few can look a lot like medical emergencies. Here’s what to look for.
Eyes Are Often the First Giveaway
The eyes respond quickly to most drugs. Cannabis causes red, bloodshot eyes (called conjunctival injection) that typically appear within two hours of use. Stimulants like cocaine and methamphetamine dilate the pupils noticeably, even in well-lit rooms. Opioids do the opposite, shrinking the pupils down to pinpoints. If someone’s pupils don’t match the lighting conditions around them, that’s one of the most reliable visual cues.
Alcohol and depressants produce a different eye sign: involuntary jerking of the eyes when they try to follow a moving object. Law enforcement officers test for this using what’s called the horizontal gaze nystagmus test, moving a pen or light slowly across a person’s field of vision. In someone who’s impaired, the eyes will jerk or bounce instead of tracking smoothly, and this jerking starts at an earlier angle than it would in a sober person.
Signs of Cannabis Use
Cannabis is one of the most commonly used substances, and its signs are fairly distinctive. Beyond red eyes, you’ll often notice a sweet, skunky odor on clothing or breath. Behaviorally, someone who’s high on cannabis may seem euphoric or unusually giggly, have difficulty concentrating or following a conversation, and react more slowly than normal. Coordination drops, which can show up as clumsiness or unsteady movements. Some people become anxious or paranoid instead of relaxed, especially at higher doses. Increased appetite and dry mouth are also common.
Signs of Stimulant Use
Cocaine, methamphetamine, and other stimulants speed everything up. A person using stimulants will often appear intensely alert, restless, and full of energy. They may talk faster than usual, jump between topics, or seem unusually confident. Their pulse and blood pressure both rise, and they may sweat despite not being physically active.
At higher doses or with chronic use, the physical signs become more pronounced. Teeth grinding (bruxism) is common with methamphetamine and MDMA. Some users develop repetitive, purposeless movements like picking at skin, sorting objects, or fidgeting with the same item over and over. Jaw clenching, twitching, and involuntary jerking of the limbs can appear. Mood can shift rapidly from euphoria to irritability, aggression, or paranoia. As the drug wears off, depression and exhaustion often follow.
Signs of Opioid Use
Opioids, including heroin, fentanyl, and prescription painkillers, produce a set of signs that’s nearly the opposite of stimulants. The person appears drowsy, sedated, or “nodding off,” drifting in and out of consciousness. Their pupils shrink to tiny pinpoints. Speech becomes slow and slurred, and they may seem confused or unaware of what’s happening around them. Their pulse slows and blood pressure drops.
The most dangerous sign to watch for is breathing rate. A respiratory rate below 12 breaths per minute is a strong indicator of opioid intoxication, and a rate below 8 to 10 breaths per minute signals a potential overdose. If someone appears unconscious, is barely breathing, and has pinpoint pupils, that combination is a medical emergency.
Signs of Alcohol and Sedative Use
Alcohol and sedatives like benzodiazepines share many of the same visible signs: slurred speech, poor balance, unsteady walking (often with feet spaced wider apart than normal), and difficulty with fine motor tasks like using a phone or picking up small objects. Blood pressure drops, and the person may seem drowsy or mentally foggy.
Behaviorally, these substances lower inhibitions. Someone may say things they normally wouldn’t, make impulsive decisions, or become unusually emotional, swinging between laughter and tears. Memory problems are common, and at higher doses, the person may not remember conversations or events. Irritability and mood swings can appear, especially as the effects fluctuate.
Signs of Hallucinogen Use
Hallucinogens like LSD, psilocybin mushrooms, and PCP produce some of the most visually obvious behavioral changes. A person may stare at ordinary objects for long periods, react to things that aren’t there, or describe sensory experiences that don’t match reality, like “hearing” colors or “seeing” sounds. Emotions shift rapidly and unpredictably. Pupils are usually dilated.
PCP stands apart from other hallucinogens because it can cause a feeling of being disconnected from one’s own body, along with aggression, poor judgment, and sometimes violent behavior. Someone on PCP may seem physically strong and unresponsive to pain, which makes the situation more unpredictable.
Behavioral Patterns Across Substances
Regardless of the specific drug, certain behavioral shifts are common across most forms of intoxication. Poor judgment and impulsive decisions show up with nearly every substance. Memory problems are widespread, affecting users of cannabis, opioids, sedatives, and club drugs alike. Mood changes that seem out of proportion to the situation, whether that’s extreme euphoria, sudden paranoia, or unexpected aggression, are another universal red flag.
Context matters too. Someone who was fine 30 minutes ago and now seems dramatically different in mood, energy level, or coordination likely experienced a rapid change caused by a substance rather than by normal fatigue or emotion. Look for clusters of signs rather than any single indicator. Red eyes alone could be allergies. Red eyes plus slowed speech, laughter at nothing, and the smell of smoke paints a clearer picture.
When It Might Not Be Drugs
Several medical conditions produce symptoms that closely resemble intoxication. Head injuries cause confusion and agitation that can look identical to being high. Low blood sugar causes slurred speech, disorientation, and poor coordination. Kidney disease and electrolyte imbalances like low sodium create a mixed picture of confusion and impaired movement that’s easy to mistake for drug use. Stroke can cause sudden speech changes and loss of coordination on one side of the body.
If someone shows signs of impairment but there’s no reason to suspect drug use, or if symptoms came on very suddenly without any prior substance exposure, consider the possibility of a medical problem. This is especially important if the person is diabetic, elderly, or recently experienced a fall or blow to the head. The distinction between intoxication and a medical condition can be life-or-death, and assuming someone is “just high” when they’re actually having a medical emergency is a dangerous mistake.
Quick Reference by Substance Type
- Cannabis: Red eyes, slow reactions, euphoria or paranoia, increased appetite, skunky odor
- Stimulants: Dilated pupils, rapid speech, restlessness, jaw clenching, elevated pulse, paranoia at high doses
- Opioids: Pinpoint pupils, drowsiness or nodding off, slow breathing, slurred speech, low pulse
- Alcohol and sedatives: Slurred speech, unsteady gait, lowered inhibitions, mood swings, memory gaps
- Hallucinogens: Dilated pupils, reacting to things that aren’t there, rapid emotional shifts, distorted perception of reality