12 Signs of  Substance Abuse in Teenagers

Normal teen behaviour is temporary, explainable, and improves with guidance or time. Drug-related behaviour tends to be persistent, extreme, secretive, and worsens despite parental involvement in contrast.

The signs of substance abuse in teens are physical, behavioral, emotional, or social, and vary depending on the type of drug being used. Here Ryan Erispe, Head of Clinical Department at The Cabin, Drug and Alcohol Rehab in Thailand, looks at how to spot the signs and symptoms of teens using legal substances like alcohol and prescription medications, as well as illegal drugs (cocaine and heroin).

Signs of substance abuse in teens include mood swings, secrecy, loss of interest in activities, poor school performance, red eyes, fatigue, and changes in friend groups or hygiene. Substance abuse in teens shows signs of anxiety, depression, or irritability.

12 signs of drug use in teens:

• Bloodshot Eyes
• Mood Swing
• Lack of Motivation
• Poor Hygiene
• Anxiety or Depression
• Secretive behaviour
• Declining Academic Performance
• Sudden Weight Loss or Gain
• Unusual Body Odours
• Changes in Friend Groups
• Irritability or Aggression
• Withdrawal from Family Activities

1. Bloodshot Eyes

Bloodshot eyes are a physical sign of drug use, characterized by the redness or glassiness of the eyes caused by the enlargement or irritation of blood vessels in the white part of the eye. It occurs after using substances like marijuana, alcohol, or stimulants, which affect blood pressure, cause dryness, or dilate blood vessels.

2. Mood Swings

Mood swings are a behavioral and emotional sign of drug use, marked by rapid and unpredictable changes in a person’s emotional state, such as sudden shifting from happiness to anger, or from calmness to irritability. The changes are triggered by the way drugs affect brain chemistry, which interferes with neurotransmitters like dopamine or serotonin.

3. Lack of Motivation

Lack of motivation is a behavioral and emotional sign of drug use, characterized by a noticeable drop in drive or interest to engage in everyday activities such as school, work, or hobbies. Lack of motivation stems from the way certain substances, such as depressants like marijuana or opioids, affect brain function, reducing energy levels and altering reward pathways.

4. Poor Hygiene

Poor hygiene is a behavioral and physical sign of drug use, defined by a noticeable decline in personal cleanliness and grooming habits such as not bathing regularly, wearing dirty clothes, or neglecting dental care. Substance use impairs judgment, lowers energy levels, and shifts priorities, causing individuals to ignore routine self-care.

5. Anxiety or Depression

Anxiety or depression are emotional signs of drug use, characterized by persistent feelings of worry, fear, sadness, hopelessness, or low self-worth. Anxiety conditions are triggered or worsened by drug use, as many substances alter brain chemistry and disrupt emotional regulation. Stimulants, depressants, and hallucinogens all contribute to mood disorders, either during use or withdrawal.

6. Secretive behaviour

Secretive behavior is a behavioral sign of drug use, defined by a person’s tendency to hide their actions, lie about their whereabouts, avoid eye contact, or become defensive when asked questions. Teens using drugs start locking doors, changing friend groups, or being vague about their activities to avoid detection.

7. Declining Academic Performance

Declining academic performance is a behavioral sign of drug use, marked by a noticeable drop in grades, missed assignments, poor concentration, or lack of participation in school activities. Drug use impairs memory, focus, and motivation, making it difficult for teens to keep up with academic demands.

8. Sudden Weight Loss or Gain

Sudden weight loss or gain is a physical sign of drug use, characterized by rapid and noticeable changes in body weight that are not due to diet or exercise. Stimulants (cocaine or methamphetamine) suppress appetite and lead to weight loss, while others, like marijuana or some depressants, increase appetite and cause weight gain.

9. Unusual Body Odors

Unusual body odors are a physical sign of drug use, referring to strange or strong smells coming from a person’s breath, skin, or clothing that are not typical for them. Certain drugs cause chemical changes in the body that produce distinctive odors such as the smell of alcohol, marijuana smoke, or the chemical scent associated with methamphetamine or inhalants.

10. Changes in Friend Groups

Changes in friend groups are a behavioral sign of drug use, defined by a sudden shift in the people. A teen spends time distancing themselves from longtime friends and associating with new peers who are involved in substance use. The changes are driven by the desire to hide drug use, seek acceptance, or avoid judgment.

11. Irritability or Aggression

Irritability or aggression are emotional and behavioral signs of drug use, characterized by frequent anger, frustration, or hostile reactions that are out of proportion to the situation. The outbursts result from the way drugs disrupt brain chemistry, lower impulse control, or trigger mood swings during intoxication or withdrawal.

12. Withdrawal from Family Activities

Withdrawal from family activities is a behavioral and emotional sign of drug use, marked by a teen’s increasing reluctance to participate in family events, conversations, or routines they once enjoyed. The distancing stems from guilt, fear of being discovered, or a growing emotional disconnect caused by drug use.

Advice on How to Approach a Teen Suspected of Substance Abuse

Ryan comments: “Approach a teen suspected of drug use with calm, nonjudgmental concern in a private, supportive setting. Focus on open communication, express specific observations, avoid accusations, and offer help rather than punishment. How parents/adults approach them greatly influences whether they open up or shut down. Choose a calm, private time to talk, and avoid reacting with anger or fear. Teens are more likely to respond when they don’t feel attacked. Use “I” statements such as “I’ve noticed you’ve been more withdrawn and your grades have dropped. I’m worried about you” to express concern without blame.

Teens are more willing to open up when they feel heard and respected. Pointing out specific changes, like shifts in hygiene, mood, or friend groups, shows attentiveness rather than accusatory. Listen actively and without interrupting, even if the conversation is difficult.

Offer support through a counselor, therapist, or addiction specialist. Avoid ultimatums, which drive secrecy or defiance. Empathetic intervention leads to better outcomes and reduces long-term harm.

Maintain trust while setting clear boundaries. Be firm about the risks of drug use, but always pair that with consistent support. The role is not just to correct, but to guide and protect them through a vulnerable time.”

The most abused substances by barely legal teens include alcohol, marijuana, and nicotine, with the use of vapes. Prescription drugs like painkillers or stimulants, and even over-the-counter medications like cough syrup, are misused. Teen addiction is essential to talk openly about the risks, stay involved in their lives, and encourage healthy activities. Setting clear rules, being a good role model, and seeking help early if you notice warning signs make a big difference.