Key Points

  • Drugs are classed according to their chemical makeup, mechanism of action, and legality.
  • Some drugs have more than one classification.
  • Most medical professionals use classifications published in the annual Physician’s Desk Reference and the American Hospital Formulary System.
  • The DEA designed a schedule that categorizes drugs by their medical uses and potential for abuse and misuse.

Drugs are classified in many different ways. In fact, there are hundreds of drug classifications. The most commonly referred to are listed in the American Hospital Formulary System (AHFS) and the U.S. Food and Drug Administration (FDA) drug class schedule.[1][2] Publications and medical facilities often refer to AHFS as well as The Physician’s Desk Reference for general purposes.[3][4]

Additionally, they can be classed as:

  • legal or illegal
  • over-the-counter or prescription
  • medical use or non-medical use

Some drugs are also listed in the federal drug schedule, which ranks them into five categories based on their benefits compared to their potential for abuse and misuse.[5]

General Drugs Classes: Based on Mechanism of Action 

Drugs are grouped into pharmacologic classes based on their mechanism of action (MOA), physiologic effect (PE), and chemical structure (CS).[6]

Standard pharmacological drug classes based on MOA include:[1]

  • Cyclooxygenase-2 (COX-2) Inhibitors: Drugs that treat pain by inhibiting prostaglandin synthesis. Examples include celecoxib and rofecoxib.  
  • Histamine 2 Receptor (H 2 R) Blockers: Drugs that treat acid reflux by blocking an acid-producing receptor. They include famotidine and cimetidine.
  • Analgesic Drug: Painkillers. 
  • Nonsteroidal Anti-Inflammatory Drugs (NSAIDs): These drugs are analgesic and anti-inflammatory. They include diflunisal and ketorolac. 
  • Selective Serotonin Reuptake Inhibitors (SSRIs): Drugs that selectively block the uptake of serotonin to treat depression and other mental health disorders. Examples include sertraline and citalopram. 
  • Proton Pump Inhibitors (PPIs): Drugs that treat ulcers and acid reflux by inhibiting enzymes that produce stomach acid. Examples are lansoprazole and omeprazole. 
  • Prokinetic Agents: Drugs that treat delayed gastric emptying and acid reflux. Examples include senna and bisacodyl. 
  • Hydroxymethylglutaryl Coenzyme A Reductase Inhibitors (HMG CoA RIs): Drugs that inhibit a specific liver enzyme to reduce cholesterol levels. They include statins such as atorvastatin, lovastatin, and pravastatin. 

Drugs Classes: Chemical Makeup

close up of different drugs in pills and capsules on table

Drugs are also divided into classes based on their chemical makeup. 

Examples of drugs classed by chemical makeup include:[7]

Alcohol

Alcohol is the most used and abused worldwide, and it is highly addictive. According to the National Institute on Drug Abuse, alcohol use disorder is the most common type of substance use disorder in the United States.[8] Substances in this class include beer, wine, and whisky. These substances work as central nervous system depressants, causing the user to feel relaxed and euphoric.[9] They also seriously impair a person’s judgment and reaction times. 

Barbiturates

Barbiturates treat people with psychiatric disorders and sleep disorders.[10] Like alcohol, these substances slow down the nervous system, causing the user to have delayed reactions and impaired motor skills.[10] Substances in this class derive from the chemical barbituric acid and include luminal, phenobarbital, and amytal.[10] 

Benzodiazepines

Medications in this class work on GABA-A receptors in the brain.[11] They are commonly prescribed to treat individuals with sleep disorders or psychiatric conditions like post-traumatic stress disorder or panic disorder. They include Ativan, Valium, and Xanax. Although benzodiazepines are helpful, they are also very commonly abused and highly addictive.[12] 

Opioids

Opioids, also called opiates, derive from opium or synthetic chemicals used to mimic its structure.[13] They mainly work by activating opioid receptors tied to pleasure and pain, leading to a surge of dopamine, the feel-good hormone.[13] Although they are prescribed to treat severe pain, they are very addictive. Unfortunately, many people abuse non-prescribed opioids for their euphoric effects.[13] 

Well-known opioids include heroin, fentanyl, and oxycodone.[14] 

Cannabinoids

Cannabinoids resemble tetrahydrocannabinol (THC), the compound in marijuana that creates intense euphoria.[15] While many people use cannabinoids for this reason, they also experience side effects like poor memory and slowed reactions.[16] Drugs in this class are heavily abused due to their accessibility and a lower potential for a deadly overdose. Hashish, as well as marijuana, are considered cannabinoids. 

Drugs Classes: Psychological Affect

Another way to classify drugs is based on their psychological effects. Though there are many classes, these are the most common. 

  • Depressants: These are often referred to as ‘downers’ since they cause the user to feel relaxed. Alcohol, opiates, and barbiturates are all considered depressants.[17] 
  • Stimulants: Substances in this category are sometimes called ‘uppers’ as they cause the user to feel a rush of energy.[18] Stimulants like caffeine and Adderall can help boost performance and increase productivity, but others like cocaine and meth cause poor concentration and increase the potential for accidents.
  • Hallucinogens: These substances cause the user to “trip” or experience audible and visual hallucinations.[19] They can be quite scary and cause the user to suffer from long-term mental health issues after use.[19] Hallucinogens are less addictive than other drug classes, but using them is just as risky.[20] Substances in this category include LSD, psilocybin mushrooms (shrooms), and PCP. 
  • Inhalants: Chemicals ingested through huffing or breathing are classified as inhalants. Most inhalants are substances not intended for human consumption, such as spray paint, nail polish remover (acetone), or gasoline. Inhaling these substances can cause instant highs and hazardous health effects.[21]

Drug Classes: Controlled Substance Act

The U.S. Drug Enforcement Administration classifies illegal and prescription drugs, substances, and chemicals into five categories based on their potential for abuse and medical use. [5] Schedule I drugs are the least helpful, while Schedule V drugs are the most beneficial and less addictive. 

These categories (schedules) include:[5]

  • Schedule I: Drugs with no accepted medical uses and a high potential for abuse and misuse. They include LSD, marijuana, ecstasy, and peyote. 
  • Schedule II: Dangerous drugs with a high potential for abuse that lead to dependence. Examples include cocaine, oxycodone, fentanyl, and Adderall. 
  • Schedule III: Substances with no medical use and a high potential for dependence, though less than schedules I and II. They include, but are not limited to, ketamine, anabolic steroids, and Tylenol with codeine. 
  • Schedule IV: Substances with a low potential for abuse and dependence. They include, but are not limited to, Xanax, Soma, Darvon, and Ativan. 
  • Schedule V: Substances that have a lower potential for abuse than Schedule IV substances. Examples are Robitussin AC, Lyrica, and medications with less than 200 mg of codeine per 100 ml. 

If your doctor prescribes an addictive medication, it indicates that they believe the benefits outweigh the risks. They will usually start you on a low dose, which is gradually increased as needed. To prevent withdrawal, they may also have you follow a tapering schedule, reducing the risk of misuse and addiction over time.