Common Drug Classifications: What They Are and Why People Use Them

Medical and illicit drugs are often sorted into categories based on their chemical makeup, their uses, or their effects. While there is no perfect system for classifying the large variety of drugs that exist today, these groupings allow patients, medical professionals, and the justice system to differentiate between substances. Becoming familiar with the common drug classifications help you gain perspective on how the substances work and why people use them, which will lead to a broader understanding of addiction.

Drug Classifications


The Purpose of Drugs Classification

Drug classifications exist to organize psychoactive substances into categories. The three main forms of drugs classification are chemical components, effects, and legal standing. The drugs within the specific categories in each type of classification can vary, though. For example, two substances can both fall within the stimulant category based on their effects, but they each may belong to different legal categories.

Substances within the same category often have similar uses and impacts on the body, so drugs classification can be especially helpful for medical professionals and their patients. The medical and psychological treatment for addiction to drugs within the same chemical category is often similar. By identifying the classification of the drug the patient is dependent on, the healthcare team already has a general framework that they can use to form a treatment plan.

There are disagreements among experts about categorizing drugs, though. Some medical professionals advocate for certain substances to be moved to different legal categories so that the penalties for use or possession are more or less severe. Although changing the official legal category of a substance is rare, it does occasionally happen.

Drug Classifications Based on Chemical Components

Although the substances within each chemical classification aren’t exactly the same, they share many chemical similarities. On a molecular level, they have a similar effect on the mind and body. Drugs within the same chemical category also usually have comparable withdrawal symptoms and require the same medical treatment during detox.

Here are the five main categories of drugs based on their chemical makeup:


Alcohol has a wide range of effects on the brain and body, and it has both short-term and long-term health impacts. The substance can create a feeling of euphoria and relaxation, but these sensations come at the cost of your sense of judgment and your motor skills. Alcohol can change the chemistry within your central nervous system after long-term misuse, and it can lead to severe liver damage.


Barbiturates are derived from the substance barbituric acid. They act on the central nervous system by slowing down its processing and functioning. Medically, barbiturates can treat sleep disorders and certain mental health conditions. However, they are highly addictive and dangerous when consumed in large amounts.


Benzodiazepines are substances that interact with the neurotransmitter gamma-aminobutyric acid-A, or GABA-A. This neurotransmitter is a main inhibitor in the central nervous system, so it acts to block certain messages that are passed between your neurons. Doctors commonly prescribe benzodiazepines to treat anxiety and sleep disorders, but these medications are very addictive and are often taken recreationally.


Cannabinoids are substances made from the compounds in the cannabis plant. These drugs create feelings of euphoria and happiness, but they can also cause anxiety and paranoia in some people when consumed in larger amounts. While cannabinoids have some approved medicinal uses, their legality varies from state to state.


Opioid drugs are either derived naturally from the opium poppy plant or synthetically from chemicals that are designed to mimic the effects of opium. These substances are sometimes prescribed to alleviate acute or chronic pain, but they can be extremely addictive. Opioids block the pain signals that the body sends the brain, and they can have a marked effect on your mood. Prescription opioids include medications like OxyContin and Vicodin, but heroin is a commonly abused illegal opioid.

Drug Classifications Based on Effect

In addition to classifying drugs based on their chemistry, experts sometimes categorize drugs based on their effects. The following are the four classifications within this system:


Like the name suggests, depressants bring your mood and energy level down. They are sometimes used medicinally to alleviate anxiety and help with sleep, but many depressants are used recreationally to alter one’s mood. Alcohol, opiates, and benzodiazepines all fall within this category. Although the specific effects vary from drug to drug, some of the common symptoms of excessive depressant use include drowsiness, mood swings, impaired judgment, and slowed reaction time.


In many ways, stimulants have the opposite effect as depressants. These substances make you feel much more awake and alert, but misuse can lead to feelings of anxiety, tension, or paranoia. Common stimulant drugs include Adderall, nicotine, cocaine, and methamphetamine. Both legal and illegal stimulants have a strong potential for misuse because they create short-term feelings of euphoria and excitement. They are highly addictive, though, and they can have a severe impact on your physical health.


Hallucinogens are substances that alter your awareness and perception of your reality. Under the influence of a hallucinogenic drug, you might experience visual or auditory hallucinations as well as an enhanced mood or euphoria. While these substances aren’t as physically addictive as many other classifications, they have a dramatic impact on your judgment and perception, so they may cause you to make unsafe decisions.


Inhalants are substances that you inhale to feel a mental or physical “high.” The effects of inhalants are usually short-lived, but they have dangerous health risks. Many of the inhalants that people misuse are not meant for human consumption, so the chemicals they contain can affect your central nervous system, your respiratory system, and other factors. Examples of inhalants include paint thinner, aerosol sprays, and gasoline.

Drug Classifications Based on Legality

In the eyes of the law, there must be clear distinctions between different types of drugs so that the justice system can determine appropriate penalties for use or possession. For example, possession of large quantities of an illegal substance carries a different penalty than misuse of a prescription medication. The legal system for classifying drugs provides a framework for state and federal courts to assess the severity of the crime. Here are the five classifications of controlled substances in the United States:

Schedule I

Schedule I drugs are considered the most dangerous and addictive substances, so they carry the harshest penalties. These substances don’t currently have an accepted medical use, so defendants cannot justify having them in their possession. Examples of Schedule I drugs include heroin, LSD, and ecstasy.

Schedule II

Schedule II drugs also carry harsh penalties for possession or misuse, but there are certain acceptable uses of these substances in the medical field. Many opioids fall within this category because they’re prescribed by doctors but are also highly addictive and dangerous to use without medical supervision. Common Schedule II drugs include OxyContin, methadone, and fentanyl.

Schedule III

Schedule III drugs have accepted medical uses and a low to moderate risk of misuse and addiction. The penalties for illegal possession of a Schedule III substance are typically less harsh than the penalties for possession of a Schedule II substance. Examples include anabolic steroids, ketamine, and codeine mixed with aspirin or Tylenol.

Schedule IV

Schedule IV drugs have a fairly low risk of misuse or addiction, so the legal penalties for possession are not as severe as for many other substances. However, this does not mean that they are completely safe or acceptable to use without medical supervision. Common Schedule IV drugs include Xanax, Ambien, Valium, and Tramadol.

Schedule V

Schedule V substances carry the mildest penalties for possession and the fewest regulations because they have a low potential for abuse. Examples of Schedule V drugs include Lyrica, Parapectolin, and Lomotil.

Knowing the Limits of Drug Classifications

People with substance use disorders can struggle with drugs in any of these classifications. Unfortunately, patients sometimes use the classification of a substance to justify using it. For instance, it can take a long time for someone to come to terms with their alcohol use disorder because alcohol is legal and widely available. However, alcohol is the most misused substance in the United States.

Similarly, people may understate the severity of their addiction if they’re using a Schedule IV or V drug. Although these substances may not have as much potential for misuse, it is still possible to abuse them or feel dependent on them to regulate your mood.

No matter which substance or category of substance you or a loved one is struggling with, it’s important to seek professional help. Substance use disorders are complex and challenging mental health conditions, but many people overcome addiction with medical and psychological support. Understanding the common drug classifications can help you better understand your experiences with substance use, but you should always consult an expert about your personal situation if you’re concerned about your drug use habits.