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Drug Classifications: Understanding How Drugs Are Classified

May 23, 2022

Table of Contents

What will this drug do to your body if you take it? What other drugs are similar to the one you're about to take? What might be the risks of the drug I’m about to take, and do they interact with others I’ve recently consumed?

Drug classifications help answer some of these questions and more.

Option 1: Classify Drugs by Chemical Makeup

Examining the structure of addictive and mind-altering drugs, and grouping like with like, can help treatment professionals assist their patients and someone experimenting with a new drug know what they might be getting into. 

If you use a system that classifies by chemical makeup, there are six major types of drugs:

  1. Alcohol
  2. Barbiturates
  3. Benzodiazepines
  4. Cannabinoids
  5. Hallucinogens
  6. Opioids and opiates


Walk through most grocery stores, and you'll see an aisle dedicated to this particular addictive substance. For many people, alcohol is a daily reprieve, and many use it in modest amounts with no adverse consequences. But it comes with its downsides. . 

Excessive drinking led to more than 140,000 deaths in the United States between 2015 and 2019.[1]

Alcohol stands alone in this classification system, as no other drug works on brain and body cells in quite the same way. It affects many of the neurotransmitters in the brain and is a bit of a “dirty drug”. It can make people feel calm, relaxed, and sedated. But it can also cause a spike of euphoria, and people lose inhibitions. Like all drugs that are habit forming, when used regularly and to excess it changes brain chemistry, and leads to withdrawal when it suddenly is stopped. Withdrawal from alcohol can be dangerous, and some people experience hallucinations and seizures when they attempt to quit drinking. 

Because it works in a unique manner, it has its own category.


Seconal and Nembutal are examples of barbiturates. Doctors might prescribe a short course of these drugs if you can't sleep, feel anxious, or have twitching muscles. 

People who misuse these drugs report feeling similar to how they feel when drunk. Continued misuse leads people to need bigger and bigger doses to experience the same degree of sedation, and people who continue to use can grow physically and ultimately psychologically dependent on these drugs. 

The more they take, the more likely they will take a lethal dose. The risk of severe poisoning rises with continued use.[2] 

Barbiturates are prescription medications with a well-defined and documented chemical makeup. Anything with this chemical signature is included within this classification.


Klonopin, Xanax, and Valium are all benzodiazepines. Originally, these medications were designed to treat conditions once addressed by barbiturates, such as seizures, agitation, anxiety and insomnia, and doctors considered them safe for long-term use. But they, too, are habit-forming. Furthermore, especially if combined with other sedating drugs, they can cause overdose and death if consumed in excess quantities.

Most people use benzodiazepines to reduce anxiety and irritability. Some people use benzodiazepines to cope with the symptoms associated with an ongoing addiction to opioids or amphetamine drugs. The sedating impact of benzos can help them come down from a speed-based high and reduce the agitation during opioid withdrawal.[3] 

But benzodiazepines can also cause euphoria at high levels. They are also habit forming and notoriously hard to stop, once people become physically dependent on them.


Marijuana and its various products are included within the classification. These drugs are the most misused substances still considered illegal at the federal level.[4] 

Most marijuana products come from a plant, but artificial versions exist. Anything with a chemical structure similar to marijuana is included in this class. 


Natural products like mushrooms and lab-created substances like ecstasy are included in this classification. These drugs alter reality and put the user into a dream-like state. 

Anything with a structure similar to other hallucinogens is included within this class. 

Opioids and Opiates 

Natural products (like opium) are opiates. Lab-made products (like Vicodin) are opioids. Today, both opiates and opioids are referred to as opioids.

Painkilling ability combined with euphoria defines the impact of substances in this class. 

Opioids are generally considered safe when taken in small doses for a short time and as prescribed by a doctor.[5] But very high doses can suppress the body's core processes and lead to death.  They are extremely habit-forming and carry a high risk of death by overdose.

Option 2: Classify Drugs by Effect 

People misuse drugs to make a specific type of change in how they feel or experience the world. 

In this system, there are five drug classifications:

  1. Central nervous system depressants
  2. Central nervous system stimulants
  3. Hallucinogens
  4. Marijuana 
  5. Opiates and opioids 

Central Nervous System Depressants

Drugs in this category are commonly known as downers. They slow down activity within the brain and deliver a sleepy, calm effect. In high doses, these substances can also cause euphoria.[6]

Both barbiturate and benzodiazepine drugs are included in this class, as they both slow down brain activity. Newer prescription drugs, like sedative-hypnotic sleeping remedies, are also included here. And since alcohol can depress brain activity, it's found here too. 

Central Nervous System Stimulants 

Drugs in this category are commonly called uppers. Prescription medications like Ritalin, and illicit drugs like methamphetamine, can speed up electrical synapses in the brain and fill people with energy. 

Anything with the ability to produce a burst of energy is included within this stimulant class. 


This classification will seem familiar to you. Just as we saw in classifications by chemical makeup, this grouping of drugs includes mushrooms, LSD, ecstasy, and similar mind-altering substances. About 7.1 million people use drugs like this every year.[7]


Again, this group is very similar to the one we saw in classifications by chemical makeup. Natural cannabinoid products like marijuana, along with lab-created versions, are both included in this group. 

Marijuana gets its own classification in this scheme as it can work like an upper, a downer, and a hallucinogen all at the same time.[8] Since no other substance works quite like this, it deserves its own group. 

Opiates & Opioids

Prescription painkillers and natural products like opium are central nervous system depressants. People who take them feel calm, relaxed, and sedate. 

But the painkilling aspect makes them slightly unique and deserving of their own class. Substances like Klonopin can't take pain away, but a drug like Vicodin might. 

Option 3: Classify Drugs by Legal Status

Most countries have a formal grouping system for drugs that help authorities determine whether a substance is legal or there are consequences for possession. Most of these systems classify a drug based on how dangerous a substance is, how much risk there is of developing an addiction, along with how helpful it might be for someone in need. 

Classification systems like this can also help doctors. Some substances require special licenses for dispensation.[9] 

The U.S. Drug Enforcement Administration assesses and groups drugs in America. There are five groups, and the lower the number, the more dangerous the substance.[10]

Schedule I

Dangerous drugs with no approved medical application are included here. Heroin, LSD, ecstasy, and marijuana are all incorporated in this category. 

Each one of these drugs works on different systems, has a different chemical makeup, and causes a different impact on a user. But according to government officials, these substances are all the same in their potential benefits relative to their dangers. 

Schedule II

Drugs with a high dangers and addiction-risk but also with potential benefits are included within this class. Combination drugs like Vicodin, along with pure substances like fentanyl, Adderall, and Dexedrine are all included here. 

Notice that there are both uppers and downers in this class. Again, this system isn't made to help officials understand how these drugs are made or what they do. Instead, this grouping has to do with dangers and addiction potential relative to potential benefits. 

Schedule III

Ketamine, anabolic steroids, and some codeine formulations are included in this group. Substances that can be dangerous at high doses but also have high therapeutic potential are all meant to be Schedule III drugs. 

Schedule IV

Drugs that have a low risk of abuse and that don't tend to cause physical dependence but are not entirely free of risk are all included in this group. Substances like Ambien, and  Xanax are  included here, as are some alternative pain killers (tramadol).

Schedule V

Substances in this class have an even lower risk of abuse than Schedule IV drugs, but still contain limited quantities of habit forming drugs like narcotics. Examples include codeine-containing cough syrups or anti-diarrheal medications such as lomotil.   

4 Reasons Drug Classifications Matter 

There are several reasons why classifying drugs correctly matters and is critical. 

1. Preventing Interactions

Combining drugs that work on the same system or bring about the same effect can quickly lead to an overdose. Drinking alcohol or taking opioids while taking benzodiazepines, for example, can slow down breathing rates to a life-threatening degree because they all have sedative effects.

Classifications help doctors and drug users know, at a glance, whether the substance they mix will have a chance of interacting and causing more risk of overdoes.

2. Assisting Law Enforcement

Should you face consequences for the substances in your backpack? And how long should your sentence be? 

Without drug classifications, no one would be able to answer these questions, which could impact your ability to get a fair trial. 

3. Helping You Heal 

Some of the treatments for a substance use disorder involve medications. A common approach in medications for addiction treatment (MAT) is to give someone a long-acting version of the drug to which you have developed a problem. For example someone with a heroin problem will be treated with methadone, a much longer-acting opioid. Knowing the drug classes helps guide treatment.  

4. Allowing Meaningful Conversations

If researchers and drug users don't share terminology, surveys are ineffective.[11] 

Classifications everyone agrees upon can ensure that everyone is using the same language, which can help everyone understand the scope of drug misuse.

Can We Use Classifications To Determine Dangerousness??

Although classifications are useful for this purpose, none of the systems is ideal.

Fentanl is classified as a Schedule II drug , making it seem slightly less dangerous than other prescription painkillers. But this same drug is now largely responsible for the recent rise in death by overdose, called a "mass poisoning." [12]

Similarly, some say that drugs in the methamphetamine class should be considered the most dangerous as these drugs often require emergency intervention after over-use.[13] But are stimulant medications like Ritalin truly more dangerous than substances like alcohol that are completely legal? Some disagree. 

Although the DEA scheduling was designed for legal purposes, to help officers define the most dangerous drugs that need the highest levels of prosecution for distribution or possession, how some of the drugs have been classified might be questionable. While almost 400,000 people are in prison for drug offenses, it's still hard to suggest that misusing a substance like mushrooms is more dangerous than drinking alcohol.[14]

In general, using a drug to excess or in a manner other than how it’s prescribed is always dangerous. If you're struggling with substances, ask for help today. There is hope in recovery.

Medically Reviewed By Claire Wilcox, MD

Claire Wilcox, MD, is a general and addiction psychiatrist in private practice and an associate professor of translational neuroscience at the Mind Research Network in New Mexico; and has completed an addictions fellowship, psychiatry residency, and internal medicine residency. Having done extensive research in the area, she is an expert in the neuroscience of substance use disorders. Although she is interested in several topics in medicine and psychiatry, with a particular focus on substance use disorders, obesity, eating disorders, and chronic pain, her primary career goal is to help promote recovery and wellbeing for people with a range of mental health challenges.

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  1. Alcohol Use and Your Health. Centers for Disease Control and Prevention. April 2022. Accessed May 2022. 
  1. Barbiturate Intoxication and Overdose. U.S. National Library of Medicine. July 2021. Accessed May 2022. 
  1. Benzodiazepines. Alcohol and Drug Foundation. November 2021. Accessed May 2022. 
  1. Marijuana and Public Health. Centers for Disease Control and Prevention. June 2021. Accessed May 2022. 
  1. Opioids. National Institute on Drug Abuse. Accessed May 2022. 
  1. Depressants. Department of Justice. April 2020. Accessed May 2022. 
  1. Hallucinogens and Dissociative Drugs Research. National Institute on Drug Abuse. February 2015. Accessed May 2020. 
  1. Cannabis (Marijuana) Research Report. National Institute on Drug Abuse. July 2020. Accessed May 2022. 
  1. Drug Enforcement Administration Drug Scheduling. National Library of Medicine. August 2021. Accessed May 2022. 
  1. Drug Scheduling. United States Drug Enforcement Administration. Accessed May 2022. 
  1. How Do Researchers Categorize Drugs, and How Do Drug Users Categorize Them? Contemporary Drug Problems. 2012. Accessed May 2022. 
  1. Fentanyl: The Most Dangerous Illegal Drug in America. RAND Corporation. January 2020. Accessed May 2022. 
  1. Global Drug Survey Reveals Methamphetamine to Be the Most Dangerous Drug. Maryville University. Accessed May 2022. 
  1. Mass Incarceration: The Whole Pie 2022. Prison Policy Initiative. March 2022. Accessed May 2022. 

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