Ch. 2: Classification Systems for Different Types of Substances

As you have learned about what psychoactive substances are, the next step is to consider how they might be classified—classification systems usually highlight similarities between items included within each group and differences between groups. Two major classification schemes have significance and relevance in the U.S. The first relates to the pharmacological and behavioral effects of different substances—this system informed the structure of the second half of our course. The second scheme relates to the legal status of different substances—the Drug Enforcement Agency (DEA) schedule of drugs.

Classification by Effects

One way of organizing the very long list of psychoactive substances is in terms of their actions on the human body. It would be impossible to list them all because the list is constantly evolving: not only are new nicknames being invented all the time, new formulations (drugs) are being developed on a regular basis. In addition, some substances do not fit neatly into a single category. For example, it is difficult to know how to classify caffeinated energy drink plus alcohol beverages (e.g., Four Loko®, Joose®, Sparks+®, Jaegerbombs, or vodka with Red Bull®) since their components fall into two very different categories: stimulants (caffeine and some other ingredients) and central nervous system depressant (alcohol). (Note that premixed beverages of this type no longer are sold in most of the United States and many countries but are still produced for consumption in other nations and mixed by individuals on their own.)

In many sources, there is a distinction made between legal or illegal “street” drugs. However, this distinction has two major flaws. First, we have seen a tremendous upsurge in the illegal use of legal substances in recent years—by now, you have heard about the problem of prescription drug abuse in the news. Second, laws can change, as we have witnessed recently with states legalizing various uses of cannabis (medical and recreational uses), and legal drinking age laws that have fluctuated in the United States between 21, 18, 19, and back to 21 just since the 1970s.

The way that clinicians and researchers categorize psychoactive substances is in terms of their effects on the human body or behavior. Tables 3-10 present you with just such a list. Considering some of the substances with which you or people you know may have experience, does it surprise you to see how they are classified? You may be surprised to see alcohol classified as a depressant, or caffeine and tobacco in the same (stimulant) category as cocaine. The different substances within each category may have differences from each other. However, it is important to recognize that they also have shared common features in terms of how they affect the mind, body, and behavior. We will look into each of these different types of substances in the second half of our course. For now, we are aiming for a general overview of the picture concerning “what’s what” in the array of psychoactive substances.

Table 3. Stimulant Substances.

Examples of Stimulants

Usual Administration Route & Common Effects

amphetamines (dexadrine, bennies, black beauties, hearts, speed, uppers); attention deficit disorder and narcolepsy medications (e.g., Adderall, Concerta, Ritalin); “bath salts;”


Administration: Snorted, smoked, injected, swallowed; caffeine also chewed in gum, absorbed through skin in a patch.

Effects: Increased heart rate and blood pressure, elevated body temperature, increased body metabolism, reduced appetite, increased energy, feelings of exhilaration and mental alertness, tremors, irritability, anxiety, panic, paranoia, violence and aggression, psychosis. Increased risk of insomnia, weight loss, cardiovascular complications, stroke, seizures, addiction, fatal overdose.

cocaine and “crack” cocaine (blow, C, candy, coke, flake, rock, snow, toot)

Administration: Snorted, smoked, injected.

Effects: Nasal damage from snorting, exposure to infectious diseases from injection, poor pregnancy outcomes, and see amphetamines effects above.

methamphetamine (meth, ice, crank, crystal, fire, glass, speed)

Administration: Snorted, smoked, injected, swallowed.

Effects: Severe dental problems, poor pregnancy outcomes, explosion/fire risks during production, chemical and environmental contamination from production activities, and see amphetamines effects above.

MDMA (Ecstasy, “club drug” combination of stimulants and hallucinogens of various types)

Administration: Swallowed.

Effects: Feelings of euphoria, enhanced mental and emotional clarity, sensations of lightness and floating and other hallucinations, suppression of appetite, thirst, and need for sleep, anxiety, nausea, blurred vision, faintness, high blood pressure, tremors, seizures, elevated body temperature. Increased risk of exhaustion, severe dehydration, sleep disorders, cognitive impairment, confusion, depression, aggression, impulsive behavior, fatal overdose, possible addiction.

tobacco products, nicotine (cigarettes, bidis, cigars, cigarillos, pipe tobacco, e-cigarettes, hookah tobacco, snuff, chew, nicotine patch or nicotine gum)

Administration: Smoked, snorted, chewed; absorbed through skin in a patch.

Effects: increased blood pressure and heart rate. Increased risk of chronic lung disease, heart disease, stroke, cancers (mouth, throat, stomach, pancreas, cervix, kidney, bladder, acute myeloid leukemia), poor pregnancy outcomes, overdose (young children), addiction.

Table 4. Depressants and Dissociatives

Examples of Depressant & Dissociative Drugs

Usual Administration Route & Common Effects

alcohol (ethanol, ethyl alcohol, etoh)

Administration: swallowed; some are smoked, chewed, or injected

Effects, low dose: euphoria, mild stimulation, relaxation, lowered inhibition;

Effects, high dose: drowsiness, slurred speech, nausea, emotional volatility, poor coordination, impaired perception, impaired memory, sexual dysfunction, loss of consciousness, impaired breathing. Increased risk of injury, depression, neurologic and cognitive deficits, memory loss, high blood pressure, liver and heart disease, poor pregnancy outcomes, addiction, fatal overdose.

anti-anxiety medications


dextromethorphan (DXM) in large amounts (some cough medicine formulations)

pre-anesthesia medications (rohypnol)

PCP (phencyclidine; angel dust)


sleep medications

tranquilizers (“tranqs”)

Table 5. Cannabinoids

Examples of Cannabinoids:

Usual Administration Route & Common Effects

cannabis; marijuana (blunt, dope, ganja, grass, herb, joint, bud, Mary Jane, pot, reefer, smoke, weed); hashish (“hash”);

synthetic marijuana compounds

Administration: Smoked, swallowed.

Effects: Euphoria, relaxation, slowed reactions, distorted sensory perception, impaired balance and coordination, increased heart rate, increased appetite, impaired learning and memory, anxiety, psychosis. Increased risk of respiratory effects and infections, declining mental health, addiction, unknown effect on pregnancy outcomes. Potential harm from additives.

Table 6. Opiates, Opioids, & Other Pain Relievers (Analgesics)

Examples of opiates, opioids, & other pain relievers

Usual Administration Route & Common Effects

heroin, morphine (and morphine derivatives), opium (laudanum, paregoric, gum, big O, block, black stuff), oxycodone, oxyconton, hydrocodone, percodan/percocet, fentanyl, demerol, darvon/darvocet

Administration: Injected, smoked, swallowed, snorted.

Effects: Euphoria, drowsiness and sedation, nausea, impaired coordination, confusion, constipation, slowed breathing. Increased risk of exposure to infectious diseases (hepatitis, HIV), poor pregnancy outcomes, fatal overdose, addiction. Potential harm from inconsistent dosing and additives.


Administration: Swallowed, injected

Effects: Like opioids, used to treat opioid addiction; overdose risk, slowed breathing rate

Table 7. Hallucinogens & Psychotomimetics

Examples of hallucinogenic & psychotomimetic drug

Usual Administration Route & Common Effects

LSD (lysergic acid diethylamide), mescaline (peyote), psilocybin (“magic” mushrooms)

Administration: swallowed, absorbed through oral tissues

Effects: altered perceptions and feelings; hallucination, increased heart rate, blood pressure, body temperature, numbness, dizziness, sleeplessness, possibly paranoia/panic; may develop “flashback” experiences later

Table 8. Steroids

Examples of Steroids

Usual Administration Route & Common Effects

anabolic & androgenic steroids (not to be confused with corticosteroids)

Administration: injected, swallowed, absorbed through the skin

Effects: hypertension, changes in blood chemistry, liver damage, aggression, acne, infertility and other reproductive system changes

Table 9. Inhalants

Examples of Inhalants

Usual Administration Route & Common Effects

household & industrial aerosols (paint thinner, gasoline, glue, butane, refrigerant gases) nitrous oxide/laughing gas (“whippets,” “poppers”)

Administration: inhaled

Effects: stimulant followed by depression, impaired memory, nervous system disruption, muscle weakness, damage to the cardiovascular system, loss of consciousness; risk of sudden death

Classification by DEA Schedule of Drugs

DEA logoMany drugs, medications, and psychoactive substances are classified by the U.S. Drug Enforcement Agency (DEA), determining the legal status of their distribution and the rigor with which they need to be controlled. Federal policy assigned this responsibility to the DEA and the controlled substance scheduling system informs law enforcement and criminal justice system responses at local, state, and federal levels. The status of any substance can change according to new, emerging evidence and the DEA is constantly challenged to evaluate new or modified substances as they appear on the ever-changing scene. Additionally, new approved medical uses may emerge—for example, evidence concerning the potential medical applications of cannabis/marijuana, LSD, or “magic mushrooms” may lead to the reclassification of these substances at a federal level (regardless of state and local policy). Let’s take a look at how the DEA controlled substances scheduling system is organized.

Each scheduled substance receives its classification based on evidence concerning (1) its potential for abuse and (2) whether it has current, evidence-supported medical applications in the U.S. The schedule of controlled substances runs from Schedule I to Schedule V—the value relates to the severity of controls needed. In other words, a Schedule I drug is considered to need the highest degree of control—it is the most addictive category and usually lacks approved medical use in the U.S. A Schedule V drug, on the other hand, is still subject to regulation and controlled access, but the controls required are the least intrusive. For example, heroin is a Schedule I drug and certain prescription-required cold relief products that contain low doses of more heavily controlled substances are Schedule V drugs (see Table 10). Other medications and drugs may be purchased “over-the-counter” (OTC). It is illegal to distribute (“traffic” in) any scheduled drug (I through V) without a proper license to do so (e.g., by prescription from a licensed pharmacy) and it is illegal to distribute Schedule I drugs at all (with the exception of a few research or specially approved uses).

If you wonder about any specific substances, you can check out the current status at In many instances, the DEA has scheduled the precursors or ingredients for making controlled substances, not just the controlled substance products themselves. For example, the Schedule II list includes opium poppy heads, not just opium and lysergic acid is a Schedule III while the LSD (lysergic acid diethylamide) for which it is a precursor is a Schedule I substance. Pseudoephedrine is available OTC but must be registered by a pharmacist since it can only be distributed in controlled amounts, because it is a precursor to the production of methamphetamine. Also, note that the scheduled drugs are not all “bad” drugs—in many cases, they are used in treating physical or mental health conditions. For example, methadone is a Schedule II substance used in treating opioid/heroin use disorders or Adderall® and Ritalin® are used to manage attention deficit disorder (ADD or ADHD). Also, note the situation with fentanyl—the pharmaceutically prepared medication is a Schedule II drug but the “street” or illicitly prepared (often imported) forms are Schedule I drugs.

Table 10. Scheduled drug examples (adapted from




Schedule I

No accepted medical use in the U.S., lack of accepted safety for use under medical supervision, OR some narcotic medications that are used medically; all have a high potential for abuse

heroin, LSD, cannabis (marijuana), peyote, “Ecstasy”/XTC, PCP, synthetic heroin, MMDA, “khat,” “china white fentanyl” and other forms of fentanyl not approved for medical or veterinary use

Schedule II

High potential for abuse, with use leading to severe psychological or physical dependence; has accepted use in the U.S. under medical supervision

cocaine (and crack), methamphetamine, methadone, opium poppy heads/straws/capsules, Seconal®, Tuinal®, Vicodin®, Demerol®, oxycodone (OxyContin®), fentanyl, Dexedrine®, Adderall®, Ritalin®

Schedule III

Potential for abuse exists but is not as high as Schedule I or II; moderate to low dependence potential, but higher risk than Schedule IV

ketamine, anabolic steroids, testosterone, products with less than 90mg codeine per dose (e.g., Tylenol® with codeine), paregoric (combination product containing opium), lysergic acid (precursor for LSD)

Schedule IV

Low potential for abuse or dependence.

Ativan®, Xanax®, Valium®, Darvon®, Darvocet®, Ativan® (lorazepam), Ambien®, Tramadol®, Soma®, Dalmane®, Konopin®, VIBERZI

Schedule V

Potential for abuse is lower than for Schedule IV drugs; preparations containing limited quantities of certain drugs with more stringent scheduling (certain narcotics).

Lomotil®, Lyrica®, cough preparations with less than 200mg codeine per 100ml (e.g., Robitussin AC)

The DEA scheduling system relates to the well-publicized issue of prescription abuse—individuals using prescription (controlled) substances outside of their prescribed use. They acquire the drugs outside of the legal, licensed distribution system.

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SWK 5805: Theories and Biological Basis of Substance Misuse Copyright © by Dr. Audrey Begun is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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