Table of Contents

The Most Common Illicit Substances of Abuse

All psychoactive substances act on brain chemicals, or neurotransmitters. While each drug may focus on a different neurotransmitter to produce its effects, all psychoactive drugs cause a surge of the neurotransmitter dopamine, which is responsible for feelings of pleasure.

The most commonly abused illegal drugs are marijuana, opioids, central nervous system stimulants, and central nervous system sedatives.


While marijuana is legal in a number of states, and other states have legalized medical marijuana, this drug is still listed as a Schedule I substance under the Controlled Substances Act. Schedule I drugs are classified as those that have a high risk of abuse but have no accepted medical use.

Marijuana use disorder can lead to addiction in severe cases, and the National Institute on Drug Abuse states that the disorder may affect 30% of users.


Opioids are a class of drugs derived from morphine. Heroin is an illegal opioid, while prescription painkillers like OxyContin and fentanyl are highly regulated due to their extreme risk of abuse. In fact, 23% of people who try heroin become addicted to it, and the numbers are similar for prescription opioids. In 2016, 626,000 people were addicted to heroin, a dramatic increase from the 214,000 heroin-addicted people in 2014.

Opioid overdoses, including heroin overdoses, have more than quadrupled since the 1990s. In 2017 alone, more than 47,000 people died of overdoses involving opioids, according to the Centers for Disease Control and Prevention.

Central Nervous System Stimulants

Illicit stimulants include cocaine and methamphetamine. These drugs are listed on Schedule II of the Controlled Substances Act, which means they have a high potential for abuse, but they also have some medical value. The prescription drug Adderall has a very similar chemical composition to meth, making it one of the most highly abused prescription drugs. Almost 40% of emergency room visits involve cocaine.

Central Nervous System Sedatives

Sedatives, or depressants, are a class of prescription drugs that are used to treat anxiety and sleep disorders. These include benzodiazepines like Valium and Klonopin; non-benzodiazepine sleep medications like Ambien and Lunesta; and barbiturates like Luminal and Nembutal. In 2017,1,799,000 Americans admitted to using tranquilizers or sedatives. While it’s unclear how many are addicted to sedatives, these drugs are commonly combined with other substances, including opioids and alcohol.

How Drug Addiction Develops

Addiction is caused by changes in the brain’s structures and functions resulting from heavy drug abuse. The neurotransmitter dopamine, which causes the pleasure produced by drugs, is also involved in memory, learning, and reward centers of the brain and is the primary neurotransmitter involved in addiction. Drugs produce a dopamine release that can be as much as 10 times bigger than what occurs in nature with activities like having sex, winning a game, or eating delicious food.

When you use drugs, your brain records a memory of the pleasure produced. It also records memories of environmental cues, such as who you’re with, where you are, and what you’re feeling. Once addiction develops, these cues become triggers for cravings and drug abuse.

As you continue to heavily abuse drugs, changes occur in the brain. The nerve cells in the brain’s reward center begin communicating with those in the learning and memory centers in a way that leads the brain to equate liking drugs with wanting them. The result of this communication is intense cravings and compulsive behaviors surrounding seeking out and using drugs.

Addiction leads to changes in thinking patterns as well. Even as the drug abuse upends your life and causes problems with your relationships, finances, health, and legal status, you’ll continue seeking out and using drugs.

Addiction vs. Dependence

Drug addiction and dependence are different, although these terms are often used interchangeably. Dependence is a physical reliance on drugs caused by changes in neurotransmitter activity as the brain tries to compensate for heavy drug abuse. Dependence is characterized by withdrawal symptoms that set in when you quit using cold-turkey. The symptoms of withdrawal vary by drug type, although all psychoactive drugs of abuse cause intense cravings when you quit using them.

How Drug Addiction is Diagnosed

Drug abuse, addiction, and dependence are diagnosed under the umbrella of “substance use disorder,” or SUD. The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition identifies eleven diagnostic criteria for determining whether a substance use disorder is mild, moderate, or severe. Meeting two or three criteria indicates a mild SUD, which is characterized as drug abuse, or the act of using drugs in a way that causes problems in your life. Meeting four or five criteria indicates a moderate SUD, which can denote an addiction. Meeting six or more criteria indicates a severe SUD, which likely involves both addiction and dependence. Here are the diagnostic criteria for an SUD.

In the past year, have you:

1. Used drugs for a longer period of time or in larger amounts than you intended?
2. Wanted or tried to stop using but found you can’t?
3. Spent an excessive amount of time seeking, using, and recovering from using?
4. Experienced intense cravings for drugs?
5. Continued to use drugs even though it was causing problems at work, home, or school?
6. Continued to use drugs even though it was causing problems with your relationships?
7. Lost interest in hobbies and activities you once enjoyed?
8. Repeatedly found yourself in risky situations as a result of your drug use?
9. Continued to use even though it was causing or worsening physical or mental health problems?
10. Developed a tolerance so that you need increasingly larger amounts of drugs to get the desired effects?
11. Experienced withdrawal symptoms when you stopped using?

If you or someone you love is addicted, getting professional help can not only help end the addiction for the long-term, but it can also help you restore your life.

Addiction Treatment

Around 50% of a person’s risk for addiction is genetic. The remaining 50% is a combination of environmental, social, cultural, and biological factors. Addiction almost always has underlying causes. The most common causes of addiction include mental illnesses like anxiety and depression, a history of trauma, and the kind of chronic stress that comes from life situations like poverty or abuse.

Mental illness, trauma, and stress all lead to self-medicating with drugs in an attempt to feel better and cope with negative emotions. They also make it difficult to stop using once heavy abuse has started. Addiction treatment is largely focused on addressing the underlying causes of addiction. A high-quality treatment program takes a holistic approach to treating addiction that addresses all a person’s needs and underlying issues.

The first step of treatment is detox, which ends the drug dependence by allowing all traces of drugs to leave the body so the brain can return to normal functioning. Once detox is complete, addiction treatment involves a variety of traditional and complementary therapies that help individuals:

  • Address the underlying causes of the addiction and heal from them
  • Develop skills for coping with negative emotions
  • Develop healthier patterns of thinking and behaving
  • Develop skills, strategies, and techniques for coping with cravings
  • Find meaning and purpose in a life without drugs
  • Repair damaged relationships and form new, healthier relationships
  • Restore function to the household and the family system
  • Learn to relax and have fun without drugs
  • Find employment or return to school

The National Institute on Drug Abuse stresses that most people who fully engage with their treatment program and stay in treatment for an adequate period of time will recover for the long-term. For most people, treatment should last around 90 days. Anything less, according to NIDA, is of limited effectiveness.

How to Get Help for a Drug Addiction

Seeking help is often the hardest part of ending addiction. Many people are afraid of losing friends or disappointing family members. Others are afraid that they won’t know who they are or what to do without drugs, or that they’ll lose their job or social status. These are valid fears, but they’re fully addressed in treatment. The truth is, treatment helps you improve all areas of your life and enjoy greater health and happiness down the road.

  • The Substance Abuse and Mental Health Services offers a treatment locator to help individuals find a treatment program that will work for them.
  • Narcotics Anonymous provides local group meetings for individuals interested in seeking help. Their website also has a downloadable meeting app.
  • The National Suicide Prevention Lifeline has 24/7 services and can refer you to the nearest rehab facility.