You’re sitting across from someone and something just feels... off. Maybe they’re laughing a little too hard at a joke that wasn't that funny. Or perhaps they’ve been staring at the back of a cereal box for five minutes straight like it contains the secrets of the universe. We’ve all been there. You start wondering, how can you tell if someone is high on weed without making things awkward or sounding like a private investigator?
It’s not always as obvious as a giant cloud of skunky smoke or a tie-dye shirt.
Cannabis affects everyone differently. Seriously. While one person might turn into a philosopher-king, another might just fall asleep standing up. The biological reality is that THC (tetrahydrocannabinol) interacts with the endocannabinoid system, which is basically the body’s massive signaling network for mood, memory, and physical coordination. Because this system is spread throughout the entire body, the signs of being high are often a mix of physical glitches and mental shifts.
The physical "tells" that are hard to hide
The most famous sign is, of course, the eyes. Bloodshot eyes happen because cannabis causes vasodilation. Basically, the blood vessels in the eyes expand. It’s a physiological response that has nothing to do with how "hard" the smoke hit—it’s just biology. If someone’s eyes look like a roadmap of Mars, that’s a pretty solid indicator.
But look closer at the pupils. While some people claim pupils dilate, the research is actually a bit mixed on that. What's more reliable is the "droopy" look. Eyelids often get heavy. It’s that sleepy, relaxed gaze that makes it look like they’re struggling to keep their eyes at full mast.
Then there’s the mouth. "Cotton mouth" or xerostomia is a real thing. THC binds to cannabinoid receptors in the submandibular glands, which are responsible for producing about 70% of your saliva. When someone is high, those glands get a "stop" signal. If you notice someone constantly licking their lips, drinking excessive amounts of water, or if their speech sounds a bit "thick" or "pasty," they’re likely dealing with this.
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Movement changes too. You might see a slight lack of coordination. They aren't necessarily stumbling around like they’ve had six shots of tequila, but their timing is just a millisecond off. They might reach for a glass of water and slightly misjudge the distance, or move with a slow, deliberate care that feels unnatural for the setting.
Behavior and the "Stoner" headspace
If you really want to know how can you tell if someone is high on weed, you have to watch the conversation flow. Cannabis impacts short-term memory almost instantly. This leads to the classic "wait, what was I saying?" moment. They start a sentence with a lot of energy, get halfway through a story about a dog they saw once, and then—poof. The thought is gone.
Laughter is another big one. Not just any laughter, but inappropriate, uncontrollable giggling. Things that are objectively mundane become hilarious. This is because THC can stimulate the reward system in the brain, making the "humor threshold" much lower than usual.
On the flip side, some people go the opposite direction. They get quiet. Very quiet.
This is often the "paranoia" or "introspective" phase. They might be over-analyzing everything you’re saying or worrying that they look high, which ironically makes them look even higher because they’re acting so stiff. If someone who is usually chatty suddenly becomes a silent observer who jumps every time a door closes, that’s a red flag.
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The scent and the "vibe" check
You can’t talk about weed without talking about the smell. It’s pungent. Terpenes like myrcene and pinene give cannabis that earthy, skunky, or citrusy aroma that clings to fibers. Even if they’ve used a vape pen, there’s often a faint, sweet, or herbal scent that lingers on their breath or clothes.
Then there’s the munchies. This isn't just a cliché from 90s stoner movies. Research published in Nature Neuroscience suggests that THC actually "plugs into" the olfactory bulb in the brain, making food smell and taste significantly more intense. If your friend is suddenly treating a bag of generic corn chips like a five-course meal at a Michelin-star restaurant, the THC has likely kicked in.
Why it's harder to tell these days
In the past, you looked for a joint and a cloud of smoke. Now? It’s complicated.
Between high-potency edibles, dabs, and odorless vape cartridges, the traditional signs are fading. Edibles, in particular, are tricky. They take 30 minutes to two hours to kick in, and the high is much more "body-heavy." Someone on edibles might not have the red eyes or the smell, but they might seem incredibly lethargic or mentally "distant" for several hours.
Also, tolerance matters. A daily smoker might exhibit almost none of these signs. Their brain has adapted to the presence of THC, meaning they can hold a perfectly normal conversation and perform complex tasks while being "high" by any medical definition. In these cases, you might only notice tiny details, like them being slightly more relaxed than usual or having a slightly increased appetite.
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Medical vs. Recreational: A necessary distinction
It's worth noting that not everyone who looks "high" is using weed for fun. Many people use medical cannabis for chronic pain, epilepsy, or MS. For these individuals, the "signs" of being high are actually the signs of their medicine working—less tremors, less visible pain, or improved mood.
Also, certain medical conditions or even extreme fatigue can mimic the signs of cannabis use. Lack of sleep causes red eyes. Anxiety causes jitteriness. Dehydration causes dry mouth. It’s always better to observe a cluster of symptoms rather than betting everything on a single sign.
What to do if you’re sure
If you’ve gone through the checklist—red eyes, dry mouth, short-term memory lapses, and a sudden obsession with Taco Bell—and you’re sure they’re high, the best approach depends on the setting.
In a social or casual environment? Honestly, just let it be. Most people on weed are harmless and just want to relax. If they seem anxious or "greening out" (nausea and dizziness from too much THC), get them some water and a quiet place to sit. Black pepper can also help; it contains caryophyllene, a terpene that can actually help mitigate the anxious effects of THC.
If it's a professional or safety-sensitive situation, that’s different. Someone shouldn't be operating heavy machinery or driving if they’re showing these signs.
Actionable steps for identifying impairment
If you suspect someone is under the influence and need to be sure for safety or social reasons, look for these specific combinations:
- The Triple Check: Don't rely on red eyes alone. Look for the combination of red eyes, slow verbal response time, and physical relaxation (slumping or slow movements).
- The Conversation Test: Ask a question that requires a two-part answer. "What did you think of the movie, and do you want to see the sequel?" A high person will often answer the first part and completely forget the second part existed by the time they finish talking.
- Observe the "Focus" Shifts: Watch how they react to distractions. Someone high on weed often has "tunnel vision" focus on one thing (like a phone or a plate of food) and will be visibly startled if you break that focus.
- Check the Peripheral: While they might be making eye contact, look at their hands. Fidgeting with objects or a slight tremor can sometimes accompany the "up" phase of a sativa-heavy high.
- Check the Context: If it's 11:00 PM on a Friday, it's one thing. If it's a Tuesday morning and they're acting this way, consider if they are on a new medication or dealing with a health issue before jumping to conclusions.
Understanding these cues isn't about "catching" someone. It’s about understanding their state of mind and ensuring everyone stays safe and comfortable. Whether it's the glassy stare or the sudden deep interest in the texture of a velvet pillow, the signs are usually there if you know where to look.