It starts with a gut feeling. You’re sitting across from someone you’ve known for years—maybe a sibling, a partner, or a close friend—and something just feels... off. Their laugh is a beat too slow. Or maybe they’re suddenly vibrating with an energy that wasn't there ten minutes ago. You don't want to be the "narc" or the paranoid one, but the doubt is eating at you. Honestly, learning how to tell if someone is taking drugs isn't about playing detective; it's about noticing the tiny fractures in their normal baseline.
People think addiction looks like what we see in movies: the disheveled person in an alleyway. That's rarely how it starts. Most of the time, it's subtle. It's the "flu" that happens every three weeks. It's the sudden, inexplicable need for twenty dollars. It’s the way they’ve started wearing long sleeves in July, or why their pupils are the size of dinner plates in a bright room.
The Baseline Shift: Why You Need to Trust Your Eyes
Before you look at symptoms, you have to know their "normal." Everyone has a baseline. If your friend is naturally high-strung, a bit of anxiety isn't a red flag. But if your chill, laid-back cousin is suddenly pacing the living room and picking at their skin, that’s a shift.
Drugs change brain chemistry. It’s physics. When someone introduces a foreign substance—whether it’s a stimulant like cocaine or a depressant like Xanax—the body reacts in predictable but often quiet ways. You’re looking for a pattern, not a one-off bad day.
Physical Red Flags: Beyond the Bloodshot Eyes
Bloodshot eyes are the classic trope, sure. But did you know that different substances do wildly different things to the pupils? Opioids like fentanyl or oxycodone cause "pinpoint pupils." They get tiny. Even in a dark room, they won't dilate. On the flip side, stimulants like MDMA, meth, or even high doses of ADHD meds make pupils massive. If you’re trying to figure out how to tell if someone is taking drugs, look at their eyes in a well-lit room. If the black part of the eye is taking over the iris, something is likely up.
Then there’s the "Tweaker Twitch." Stimulants cause repetitive, purposeless movements. This might look like grinding teeth (bruxism), constant lip-licking, or tapping a foot so hard the floor shakes. It’s an overflow of dopamine. They literally cannot sit still.
Weight changes happen fast too. Stimulants kill the appetite. If someone drops 15 pounds in two weeks and claims they’re just "fasting," be skeptical. Conversely, heavy marijuana use or certain prescription meds can lead to a sudden "snack-heavy" weight gain.
Skin tells a story. Opiates often cause "the itch." People on heroin or pills will scratch their nose or arms until they’re raw. Meth use often leads to "crank sores"—small, picked-at scabs on the face and arms because the user feels like something is under their skin. It’s a tactile hallucination called formication. It’s heartbreaking to see, and it’s a dead giveaway.
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The Smell of the Secret
Smell is underrated. You know what weed smells like—skunky, pungent, unmistakable. But what about others?
Methamphetamine smoke often has a chemically, sweet smell, sometimes compared to burnt sugar or even cleaning supplies. Heroin, when smoked, can smell like vinegar. If their room suddenly smells like a chemistry lab or a bottle of malt vinegar, don't ignore it. Also, look for the "cover-up." Excessive use of incense, Febreze, or heavy cologne often masks the odor of smoke or the chemical musk that some drugs produce through sweat.
How to tell if someone is taking drugs based on behavioral "Glitches"
The personality shift is usually what drives families to seek help.
The biggest indicator? The "Disappearing Act." Someone who was once reliable starts missing big events. They’re late to work. They disappear into the bathroom for forty minutes at a dinner party. When they come out, they’re "refreshed" but their mood has flipped 180 degrees.
The Financial Black Hole
Drugs are expensive. Even "cheap" drugs become a massive financial burden because of the frequency of use. If someone with a decent job is suddenly asking to borrow gas money, or if small household items (jewelry, electronics, even power tools) start going missing, you’re past the point of "maybe."
According to the National Institute on Drug Abuse (NIDA), the loss of control over finances is one of the primary clinical markers of a Substance Use Disorder. It’s not that they want to steal from you. It’s that the brain’s frontal lobe—the part responsible for logic and consequences—is being bypassed by the survival instinct to get high.
Sleep Cycles and "The Crash"
Watch the clock.
Stimulant users stay up for days. They’ll be active at 4:00 AM, cleaning the kitchen or sending you long, rambling text messages about a "new business idea." Then, they’ll sleep for 20 hours straight. This "up and down" cycle is a hallmark of cocaine or meth use.
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Downers, like benzodiazepines (Valium, Xanax) or opioids, create a different kind of sleepiness. You’ll see them "nodding out." They’ll be mid-sentence, and their eyelids will just... heavy-drop. They aren't just tired. They are struggling to stay conscious. If you have to shake someone to wake them up during a normal conversation, that is a medical red flag for an overdose risk.
The Social Circle Swap
People don't usually do drugs alone at first. They find a "tribe." If your loved one has ditched their old friends for a new group of people you’ve never met—people who seem a bit rougher or who don't want to make eye contact with you—pay attention. The "old" friends represent accountability. The "new" friends represent access.
Why You Can't Always Trust the "Tests"
A lot of people run out and buy a 5-panel drug test from the pharmacy. Honestly? They’re easy to beat. Between synthetic urine, "detox" drinks, or just timing the half-life of the drug, a negative test doesn't always mean a "no."
For example, many synthetic cannabinoids (K2/Spice) don't show up on standard tests. Fentanyl often requires a specific strip; it won't always trigger a standard opiate test because it's synthetic. If the behavior says "high" but the test says "low," trust the behavior.
Paraphernalia: The "Hidden" Clues
Sometimes it’s not the person; it’s their environment. You’re looking for things that don't belong.
- Burnt spoons or bottle caps.
- Tiny plastic baggies (even if they’re empty, they often have a white residue).
- Cut-up straws or hollowed-out pens.
- Tinfoil with burn marks.
- Rolled-up dollar bills.
- Eye drops (used constantly to hide redness).
- Mouthwash or gum (to hide the smell of alcohol or "dry mouth").
The Emotional Rollercoaster
Mood swings in addiction are violent. It’s not just "being moody." It’s a sudden, irrational anger. If you ask a simple question like, "Where were you last night?" and they explode into a defensive rage, that’s a deflection tactic. It’s easier to make you the "bad guy" for asking than it is to admit they were using.
They might also experience "anhedonia." This is a fancy medical term for the inability to feel pleasure from normal things. If they used to love playing guitar or going to the gym and now they just sit in a dark room staring at their phone, their dopamine receptors might be fried from substance use. Nothing "natural" feels good anymore compared to the drug.
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Expert Insight: The Nuance of Mental Health
We have to be careful here. A lot of these signs overlap with clinical depression or ADHD. A depressed person might also lose weight, stop showering, and withdraw from friends. Someone with undiagnosed ADHD might be restless and impulsive.
The difference is usually the physical markers. Depression doesn't usually cause dilated pupils or the smell of vinegar in a bedroom. When you're trying to figure out how to tell if someone is taking drugs, you have to look for the combination of physical and behavioral shifts.
What to do once you know
So, you’ve checked the boxes. You’re 90% sure. What now?
First, don't stage a "movie" intervention while they are high. It won't work. They literally cannot process the information. Wait for the "lull"—the morning after, or when they are starting to come down and feel the weight of their choices.
Actionable Steps for Concerned Loved Ones:
- Document everything. Keep a small log of the dates and times you noticed specific behaviors. This isn't to be mean; it's to counter the "gaslighting" that often happens when an addict is confronted. When they say, "I've never done that," you can calmly say, "Actually, it happened last Tuesday, Friday, and Sunday."
- Use "I" statements. Instead of saying "You are a druggie," try "I feel scared when I see your pupils are so small and you can't stay awake." It lowers the defensiveness.
- Check the "Medicine Cabinet." It sounds intrusive, but if you suspect opioid use, check for missing pills or "doctor shopping" (multiple bottles from different pharmacies).
- Set a "Hard Boundary." Addiction thrives on "enabling." If you're giving them money for "rent" that is actually going to pills, you are unintentionally funding the habit. Stop the cash flow immediately.
- Get a Narcan kit. If you suspect opioids (fentanyl, oxy, heroin), keep Narcan (Naloxone) in the house. It’s a nasal spray that reverses overdoses. In 2026, it's available over-the-counter in most places. It saves lives.
Learning how to tell if someone is taking drugs is a heavy burden to carry. It’s exhausting to live in a state of constant suspicion. But remember, the drug changes the person; it doesn't erase them. Recognizing the signs is the first step toward getting them—and yourself—the help needed to navigate the road back to reality.
If you're seeing more than three of these signs consistently over a two-week period, it's time to have a serious, calm conversation. Don't wait for a "rock bottom" that might never come—or might be fatal. Start the dialogue now while they can still hear you.