It starts with a gut feeling. You’re sitting across from someone you’ve known for years—maybe it’s your brother, a coworker, or your best friend—and something just feels... off. Their eyes are a little too glassy. They’re talking at a million miles an hour, or maybe they’re so sluggish they can barely finish a sentence. You start Googling, wondering how can you tell if someone is on drugs without sounding like a suspicious jerk or an amateur detective.
Honesty is tough here. People aren't caricatures. Life isn't a PSA from the 90s where someone takes a hit of something and immediately starts seeing dragons. Real-world substance use is often quieter, sneakier, and buried under a mountain of "I'm just tired" or "I've been stressed at work."
If you're looking for a checklist, you have to understand that drugs don't all look the same. A person on high-grade stimulants looks nothing like a person nodding off on illicit fentanyl.
The Physical Red Flags: Beyond the Eyes
We’ve all heard about "pinned" or "dilated" pupils. It’s the classic trope. And yeah, it’s physically real because drugs mess with the autonomic nervous system. Opioids like oxycodone or heroin typically cause miosis—that’s the medical term for pupils that look like tiny pinpricks, even in a dim room. On the flip side, stimulants like cocaine or MDMA, and even some hallucinogens, cause mydriasis, making the pupils swallow the whole iris.
But eyes tell only half the story.
Look at the skin. Chronic use of stimulants often leads to "crank sores" or picking marks because the drug makes the user feel like something is crawling under their skin (formication). It’s unsettling. You might notice a graying of the skin tone or sudden, unexplained weight loss that happens in weeks, not months.
Then there’s the "nod." If you see someone drifting in and out of consciousness during a conversation—literally dropping their head and then snapping back up as if nothing happened—that’s a massive red flag for central nervous system depressants. According to the National Institute on Drug Abuse (NIDA), this "on the nod" behavior is a hallmark of opioid intoxication. It’s not sleepiness. It’s a struggle to remain conscious.
The Smell of the Secret
Smell is a massive giveaway that people try to mask with an ungodly amount of cologne or Febreze.
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- Marijuana: Everyone knows the skunky, earthy smell, but synthetic "spice" or "K2" can smell like chemically-treated potpourri.
- Meth: Often described as a sickeningly sweet or metallic smell, sometimes compared to burning cleaning chemicals or cat urine.
- Ketamine: Sometimes has a slightly medicinal or "burnt plastic" odor, though it's harder to catch.
Behavioral Shifts: The "New" Personality
When someone asks how can you tell if someone is on drugs, they usually aren't just looking at physical traits. They're looking at the fact that their friend suddenly stopped caring about their vintage car collection or their kids' soccer games.
Sudden secrecy is the big one. If someone who used to be an open book suddenly starts locking their phone, leaving the room to take every call, or getting incredibly defensive when you ask "How was your day?", pay attention. Dr. George Koob, Director of the NIAAA, often discusses how addiction hijacks the brain’s reward system. The drug becomes the only thing that matters, so social obligations and honesty just... evaporate.
They might become a "night owl" overnight. Or they might sleep for 14 hours straight on a Tuesday.
Money problems are another huge indicator. If someone with a steady job is suddenly "short for rent" or asking to borrow fifty bucks for "gas" every three days, the math usually points to a habit. Drugs are expensive. Sustaining a habit while maintaining a normal life is a full-time job that most people eventually fail at.
The Different "Highs" and What They Look Like
You can't lump everything together. A person on "uppers" is a different animal than someone on "downers."
The Stimulant Profile (Cocaine, Meth, Adderall)
Think high energy. Too much energy. They might be grinding their teeth (bruxism) or constantly licking their lips because their mouth is bone-dry. They’ll talk over you. They might get paranoid, checking behind the curtains or thinking people are talking about them in the next room. When the "crash" hits, they disappear. They’ll sleep for two days and wake up depressed, irritable, and starving.
The Depressant Profile (Alcohol, Xanax, Opioids)
It looks like a slow-motion movie. Slurred speech is the most common sign. If they sound drunk but don't smell like a brewery, it’s often benzodiazepines or opioids. They might have a "heavy" gait, dragging their feet slightly. Their coordination goes out the window. They drop things. They forget what they said five minutes ago.
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The Dissociative/Hallucinogen Profile (LSD, PCP, Ketamine)
This is the "space cadet" look. They might be staring at a wall for an hour, or acting like they’re seeing something you aren’t. With PCP, there’s often a frightening level of aggression or a lack of pain response. Ketamine can lead to the "K-hole," where the person is physically there but mentally completely detached from their surroundings.
Why You Might Be Wrong (The Nuance)
It is incredibly important to acknowledge that many of these symptoms overlap with legitimate medical and mental health issues.
Hyperactivity and rapid speech? Could be a manic episode in someone with Bipolar Disorder. Slurred speech and poor coordination? Could be a neurological issue or a reaction to a new, legitimate prescription medication. Weight loss and irritability? Could be clinical depression or a thyroid problem.
This is why "confrontation" is a dangerous first step. If you accuse someone of being high when they’re actually having a mental health crisis or a diabetic emergency, you’ve just broken a bridge that might have been their only lifeline.
The Environment: Physical Evidence
Sometimes you don't look at the person; you look at their space. Addiction leaves a trail.
You’re looking for "paraphernalia." It’s rarely a giant bong sitting on the coffee table. It’s more likely to be small, torn-off corners of plastic baggies. It’s burnt silver foil. It’s the "missing" spoons from the kitchen. It’s tiny glass tubes or even just a lot of rolled-up dollar bills or cut-up straws in the trash.
Check the bathroom. People using drugs often spend an inordinate amount of time in the bathroom because it’s the only room with a lock where no one asks questions. If "taking a shower" takes an hour and a half every single day, something else might be going on.
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What Do You Actually Do?
So, you’ve seen the signs. You’ve noticed the dilated pupils, the weird smells, and the missing money. Now what?
Don't do the "intervention" thing you see on TV with twelve people in a circle. It usually backfires. Most experts, including those from SAMHSA (Substance Abuse and Mental Health Services Administration), suggest a one-on-one approach first.
Wait until they are sober. Never try to have "the talk" while they are high. It’s a waste of breath. They won't remember it, or they'll get combative.
Use "I" statements. "I’ve noticed you’ve been sleeping a lot lately and I’m worried about you," is much better than "You’re clearly on pills and you need to stop." You want to be a safe harbor, not a judge.
Actionable Steps to Take Now
If you are certain someone you care about is struggling, here is how you handle it without making things worse:
- Document the patterns. Don't rely on memory. Note the dates and times you notice specific behaviors. This helps if you eventually need to involve medical professionals.
- Carry Naloxone (Narcan). If you suspect opioid use, keep Narcan on hand. In many places, you can get it over the counter. It saves lives, period.
- Set boundaries. You can love someone and still refuse to lend them money or drive them places. Enabling is often disguised as "helping."
- Call the professionals. Use the SAMHSA National Helpline at 1-800-662-HELP (4357). It’s confidential and they can tell you where the nearest treatment centers are.
- Take care of yourself. Dealing with someone else's substance use is traumatic. Look into Al-Anon or Nar-Anon groups. They aren't for the user; they are for you.
Identifying the signs is just the first layer. The reality is that addiction is a chronic disease of the brain, not a lack of willpower. Being able to spot the signs early can be the difference between a tragic outcome and a long road to recovery. Pay attention to the shifts in personality more than the physical ticks—the "soul" of the person usually changes before their body does.