Symptoms and Signs of Substance Abuse

Table of Contents

How to tell if Someone is Using Drugs

Drug use affects people from all walks of life and all socioeconomic statuses. Whatever the reason a person starts taking drugs, whether recreationally or as prescribed, tolerance, patterns of increased use, physical dependence and, ultimately, addiction may develop—sometimes before the user even realizes it.1

When a full-blown substance-use disorder (SUD) develops, it can be extremely difficult to stop using drugs without professional treatment.2 Drug use can wreak havoc on the body and mind and may eventually become deadly. When you realize that you or someone you love has a problem, it’s essential to get help right away. There is no shame in admitting that you need treatment for drug use; doing so can be life-saving. Learn about drug detox helplines.

Use of most substances will produce noticeable signs and symptoms. These may include physical or behavioral symptoms—most likely both.


Physical and behavioral symptoms of drug abuse.

What are Physical Signs of Drug Abuse?

Some of the most noticeable symptoms of drug use are those that affect certain physiological processes. For example, your body’s tolerance to a drug develops when a drug is used long or often enough that it adapts to the consistently elevated presence of the substance. When tolerance grows, increased quantities or strengths are required to achieve the previous effects.1

Individuals using a drug to get high may come to take such large doses to overcome their tolerance that they place themselves at increasing risk of potentially fatal overdose.3

Changes in appearance can be additional clues to possible drug use and may include:4

  • Bloodshot or glazed eyes.
  • Dilated or constricted pupils.
  • Abrupt weight changes.
  • Changes in hygiene.
  • Dental issues.
  • Skin changes.
  • Problems sleeping or sleeping too much.

Signs will vary based on the substance and the method used (i.e., smoking, injection, etc.).

What are Behavioral Signs of Drug Abuse?

Drug use tends to significantly alter a person’s behavior and habits. Some drugs can impair the brain’s ability to focus and think clearly.5

Changes in behavior, such as the following, are sometimes associated with problematic substance use:4,6

  • Increased aggression or irritability.
  • Changes in attitude/personality.
  • Lethargy.
  • Depression.
  • Sudden changes in a social network.
  • Dramatic changes in habits and/or priorities.
  • Involvement in criminal activity.

Learning to recognize the physical or behavioral signs of drug use can help prevent the problem from progressing further.

Illicit Drugs

Click on any substance below to find out some characteristic signs and symptoms of abuse and addiction for that substance and how to find help.

How much do you know about some of the most commonly abused drugs? Learn the signs and symptoms now.

Prescription Drugs




    Find out if your insurance coverage includes addiction rehab and treatment by visiting the links below:

    How do you know if you or a loved one is addicted? Find out here.


    1. National Institute on Drug Abuse. (2018). Is there a difference between physical dependence and addiction? 
    2. National Institute on Drug Abuse. (2018). Principles of Effective Treatment. 
    3. Pennsylvania Department of Drug and Alcohol Programs. (n.d.). Overdose Overview.
    4. New York State Department of Health and the Office of Alcoholism and Substance Abuse Service. (n.d.). How do I Know? I think My Child is Using Alcohol and/or Drugs. 
    5. National Institute on Drug Abuse. (2018). Drugs and the brain
    6. National Institute on Drug Abuse. (2007, January). Bringing the Power of Science to Bear on Drug Abuse and Addiction: Drugs Have Long0-term Consequences.
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