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Drug Classifications

Drug Classifications

Pharmacology, or the study of drugs and medications, is a complicated subject. One of the ways to make it easier to understand is to have a good knowledge of drug classification, or the system by which various drugs are grouped together.

How Are Drugs Classified?

Drugs are categorized in a variety of different ways. In the pharmaceutical industry, drugs are grouped according to their chemical activity or conditions that they treat. There are many reasons to classify drugs, ranging from understanding the usefulness of particular types of drugs to formulating treatment plans based on chemically similar drugs. In the world of illicit and abused drug use, there are essentially 7 different types of drugs.  Each has its own set of characteristics, effects, dangers, and side effects.

Drug categories include the following:

  • Stimulants
  • Depressants
  • Hallucinogens
  • Dissociative
  • Opioids
  • Inhalants
  • Cannabis

For Drug Enforcement Agency (DEA) purposes, these drug classifications are further distilled to 5 categories. The DEA also refers to these as schedules, and these schedules depend on the drug’s accepted and authorized medical use or the drug’s abuse and dependency potential. The abuse rate of a drug is determining factor when assigning a schedule. For example, Schedule I drugs are shown to have a high abuse rate and the potential to create significant psychological and physical dependence.1

The DEA defines physical dependence as developing when the body becomes habitually in need of a drug. Physical dependence is often exhibited both in the development of a tolerance to a drug and in the withdrawal effects that might occur if a person stops using the drug. When a person builds a tolerance to a particular substance, it takes an increasingly larger amount of the substance to experience the same effects as once occurred with smaller amounts. Withdrawal develops with prolonged or excessive use and is experienced when a drug is sharply reduced or stopped all together. Often, withdrawal symptoms are excruciating and difficult to manage, which further encourages the drug use.

Dependence on a drug is also associated with a variety of psychological and physical symptoms.  These include social problems, financial difficulty, and legal issues. Psychological dependence presents as the craving or intense need for a drug. When a person has become psychologically addicted, they might experience excessive and uncontrollable desires to use the drug. Ultimately, this can lead to drug-seeking behavior.

Legal Classification of Drugs


Schedule 1 drugs are defined as drugs that have no medical use and have a high potential for addiction and abuse. These include drugs such as heroin, ecstasy, and LSD.

Schedule 2 drugs have a high rate of potential abuse along with significant psychological or physical dependence. Examples of Schedule 2 drugs include cocaine, meth, and opioids.

Schedule 3 drugs have moderate to low potential for misuse. These include anabolic steroids, ketamine, and testosterone.

Schedule 4 drugs have low potential for dependence. Valium, Ativan, and Ambien are all Schedule 4 drugs.

Schedule 5 drugs are medications usually used for antitussive, analgesic, or antidiarrheal purposes.

There’s a large amount of disagreement even among experts on how drugs should be classified. This means that the same drug might be categorized differently under two different systems. Because of this, it’s virtually impossible to create a set of defining drug classification standards. However, here are some of the most common.

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Chemical Classifications of Drugs

  • Opioids. Opioids are derived from the drug opium or synthetic versions that mimic the chemical structure of opium. This class of drugs interacts with neurotransmitters in the brain to block signals. Opioids are powerful. They cause both intense feelings of pleasure and can block pain. Opioid addiction is significant and is increasingly becoming the most serious addiction crisis facing America today.
  • Alcohol. Alcohol is one of the most widely abused substances across the world. It’s legal to consumer alcohol in the US, even though alcohol is a central nervous system (CNS) depressant. It causes severe long-term damage to the liver. Alcohol creates feelings of pleasure and lowers inhibitions.
  • Benzodiazepines and barbiturates. These drugs function by interacting with a neurotransmitter called GABA (gamma-aminobutyric acid). These drugs impact the body and mind differently but generally create calming and sedative effects. Often prescribed to treat a variety of psychiatric and sleep conditions, they’re highly addictive.
  • Cocaine and other stimulants. These drugs accelerate the activity of the CNS making a person feel energized, focused, and alert for long periods of time. The converse reaction is that a person feels edgy, paranoid, and angry.
  • Inhalants. Mostly consumed through breathing, these drugs can exist in vapor form at room temperature. Most inhalants are found in household items so they’re often used by adolescents and children. They tend to be less addictive than other substances but are incredibly dangerous.
  • Hallucinogens. By interacting with the CNS, this class of drugs alters the perception of time, reality, and space. They might cause a user to hear things or imagine situations that don’t exist.
  • Cannabis. One of the most widely used drugs across the world. Cannabis affects the cannabinoid receptors in the brain. This drug comes in many different forms and affects each user differently.
  • New psychoactive substances. This refers to anything that’s been lab created to mimic naturally occurring drugs falls into this category. This includes synthetic cannabis, lab-created ketamine, and more.

If you or a loved one is suffering from addiction, it might feel like you’re completely alone. The good news is treatment is available. A treatment facility can tailor make a plan specific to your needs.


  1. United States Drug Enforcement Administration. (n.d.). Drug Scheduling.

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