Call us on our toll-free line
Health professionals commonly group drugs into categories such as depressants, stimulants, opioids, hallucinogens, and cannabis based on how they affect the brain, body, and central nervous system. It also pertains to their medical use and their legal status.
Understanding these drug classifications helps individuals and families recognize the potential effects, risks, and signs of substance misuse.
In Canadian clinical practice, drug classification is not used solely for legal or law-enforcement purposes. It is an essential framework that supports patient safety, accurate prescribing, and consistent standards of care.
When a patient arrives at an emergency department or an overdose prevention site, clinicians quickly categorize substances into pharmacological groups—such as stimulants, depressants, opioids, hallucinogens, and cannabis—to better understand their effects on the body and guide appropriate treatment.
For example:
• If a substance is identified as a stimulant, clinicians anticipate possible complications such as elevated heart rate, high blood pressure, agitation, or overheating.
• If a drug is recognized as an opioid, a type of depressant, medical staff immediately consider the use of naloxone to reverse potentially life-threatening respiratory depression.
Effects of certain types of drugs on an individual:
OPIOID OVERDOSE
Pinpoint pupils
Slow/Absent breathing
Slow heart rate
Cold/Clammy skin
Responds to Naloxone
STIMULANT OVERDOSE
Dilated (large) pupils
Fast/shallow breathing
Very fast heart rate
Hot/sweaty skin
No Naloxone response
Benzo/Xylazine Mix
Variable pupils
Very slow/laboured breathing
Very slow heart rate
Cold/grey skin
Partial response (breathing only)
Features
Opioid Overdose
Stimulant Overdose
Benzo/Xylazine Mix
pupils
breathing
heart rate
skin
response
Pinpoint
Slow/Absent
Slow
Cold/Clammy
Responds to Noloxone
Dilated (Large)
Fast/Shallow
Very Fast
Hot/Sweaty
No Naloxone response
Variable
Very Slow/Laboured
Very Slow
Cold/Grey
Partial response (breathing only)
This clinical classification is different from the legal scheduling system under the CDSA. For more information on the legal scheduling, see the CDSA.
The following chart shows the major drug classifications, how they affect the brain and body, and examples of substances in each category.
Drug Class
How They Affect the Body
Common Examples
Depressant
Stimulants
Opioids
Hallucinogens
Cannabis
Slows down the central nervous system, producing relaxation and sedation.
Increase alertness, energy, heart rate, and brain activity.
Reduce pain and produce feelings of relaxation by acting on opioid receptors.
Alter perception, mood, and sensory experiences.
Produces both depressant and mild hallucinogenic effects.
Alcohol, benzodiazepines, barbiturates.
Cocaine, amphetamine, methamphetamine, methylphenidate
Morphine, oxycodone, heroin, fentanyl
LSD, psilocybin, PCP, ketamine, salvia
Marijuana, hashish, THC products
DRUG CLASS
HOW THEY AFFECT THE BODY
DEPRESSANTS
STIMULANTS
OPIOIDS
HALLUCINOGENS
CANNABIS
Slows down the central nervous system, producing relaxation and sedation.
Increase alertness, energy, heart rate, and brain activity.
Reduce pain and produce feelings of relaxation by acting on opioid receptors.
Alter perception, mood, and sensory experiences.
Produces both depressant and mild hallucinogenic effects.
DRUG CLASS
COMMON EXAMPLES
DEPRESSANTS
STIMULANTS
OPIOIDS
HALLUCINOGENS
CANNABIS
Alcohol, benzodiazepines, barbiturates
Cocaine, amphetamine, methamphetamine, methylphenidate
Morphine, oxycodone, heroin, fentanyl
LSD, psilocybin, PCP, ketamine, salvia
Marijuana, hashish, THC products, shatter
Opioids are a class of drugs that act on specific receptors in the brain and body to relieve pain. They reduce the intensity of pain signals and can also create feelings of relaxation and euphoria. Medically, opioids are used to treat moderate to severe pain, especially after surgery, injury, or in cases of serious illness.
However, they carry a high risk of tolerance, dependence, and addiction because they affect the brain’s reward system.
There are 3 classifications of opioids:
Prescription opioid medications are often classified according to how they are produced. Morphine is considered a natural opioid because it derives directly from the opium poppy plant. In contrast, oxycodone and hydromorphone are semi-synthetic opioids, meaning they are created in a laboratory by chemically modifying natural compounds found in opium.
Codeine reduces the perception of pain and slows the cough reflex. It is often combined with other medications, such as acetaminophen, or found in prescription cough syrups. Although it has legitimate medical uses, codeine can cause side effects such as drowsiness, constipation, nausea, and slowed breathing.
Because it is an opioid, regular or high-dose use can lead to tolerance, physical dependence, and addiction. Misuse — especially when combined with alcohol or other sedatives — increases the risk of overdose.
Synthetic opioids are fully manufactured in laboratories and are not derived directly from the opium poppy plant. Medication such as fentanyl is a synthetic opioid used medically to manage severe pain. Carfentanil is also a synthetic opioid, but it is extremely potent and primarily intended for veterinary use in large animals.
Although these medications have legitimate medical uses, all opioids — whether natural, semi-synthetic or synthetic — carry risks of tolerance, physical dependence, and addiction when misused or used long term.
Illegal opioids can be either natural or semi-synthetic substances derived from the opium poppy. Opium is a natural opioid, obtained directly from the dried sap of the poppy plant.
Heroin is a semi-synthetic opioid, produced by chemically modifying morphine in a laboratory.
Both substances act on opioid receptors in the brain and can produce intense euphoria, pain relief, and sedation. However, their use carries a high risk of dependence, addiction, and overdose — especially because illicit products are often unpredictable in strength and may contain synthetic opioids such as fentanyl.
Prescription medications obtained outside of a pharmacy setting can be extremely dangerous. Drugs sold on the street may be counterfeit, contaminated, or mixed with powerful synthetic opioids such as fentanyl.
Even pills that look identical to legitimate prescriptions can contain unpredictable or lethal substances. Using prescription drugs without medical supervision significantly increases the risk of overdose, harmful drug interactions, and serious health complications.
Opioids should only be used carefully and under medical supervision.
Depressants are drugs that slow down the central nervous system (CNS).
Are you uncertain whether your loved one is abusing a depressant?
with depressants you can observe the following alerts:
Heart rate slows
Reduced btain activity
Impaired reaction time
Breathing slows
Muscles relaxes
Anxiety decreases
Drowsiness
the more common types of depressants:
The most widely used depressant is alcohol; it is legal and socially accepted in most cultures. Produces impaired judgment, coordination, and impulse control. Can cause dependence and severe withdrawal symptoms
Benzodiazepines (often called “benzos”) are a class of prescription medications that produce a calming effect. In Canada, most are regulated under Schedule IV of the Controlled Drugs and Substances Act, meaning they have recognized medical use but carry a high risk of misuse and dependence.
Learn more about these drugs by following the links below
Longer-term or improper use can lead to:
The medical field once widely prescribed barbiturates for anxiety, insomnia, and seizure disorders. Today, they are now less commonly prescribed due to high addiction risks and overdose.
On the street, users may refer to this drug as “Barbs,” “Red Devils,” “Yellow Jackets,” “Block Busters,” and “Goof Balls.”
Barbiturates include:
Stimulants are a class of drugs that increase activity in the central nervous system. They temporarily speed up communication between the brain and body, leading to increased alertness, energy, attention, heart rate, and blood pressure.
The medical field classifies stimulants into different categories based on their source, chemical structure, and how they affect the brain.
Here are the main classifications:
They artificially increase dopamine and norepinephrine levels in the brain, thought to improve focus and attention.
These have a high potential for addiction, heart complications, paranoia, psychosis, and overdose.
These stimulate alertness but can still lead to dependence with regular use.
Synthetic Cathinones or “Bath salts” (These can be unpredictable and dangerous due to unknown potency and chemical composition.)
While stimulants can temporarily improve focus, mood, and confidence, misuse can lead to serious risks, including anxiety, insomnia, heart problems, addiction, and, in severe cases, psychosis or overdose.
Repeated use often disrupts the brain’s natural dopamine balance, increasing the likelihood of dependence.
In short, stimulants “speed up” the body and brain — sometimes for medical benefit, but potentially with significant harm when misused.
Learn more about stimulants here.
Hallucinogens are a class of psychoactive drugs that alter a person’s perception of reality, thoughts, and sensory experiences. They can cause visual or auditory hallucinations, intensified emotions, a distorted sense of time, and changes in mood or awareness.
Hallucinogens generally fall into three main categories:
Causing profound, temporary alterations in perception, thoughts, and mood.
Dissociative drugs make a user feel out of control and disconnected from their body and environment.
Deliriants are a class of hallucinogens that cause a state of delirium, characterized by extreme confusion, inability to distinguish reality, and vivid, often terrifying hallucinations (found in Datura, deadly nightshade, and henbane)
Researchers are studying some hallucinogens for potential therapeutic use under medical supervision, but using them without medical oversight can cause unpredictable psychological effects, especially in individuals with underlying mental health conditions.
Often classified separately due to mixed stimulant, depressant, and hallucinogenic properties. Marijuana, also known as cannabis, is a psychoactive substance derived from the Cannabis plant.
It contains chemical compounds called cannabinoids, the most well-known being THC (tetrahydrocannabinol), which produces the “high” or intoxicating effect.
Shatter, a more potent form of marijuana, is also known as BHO, Butane Hash Oil, and Honey Oil, to name a few. CBD (cannabidiol), on the other hand, does not cause intoxication but may have calming or therapeutic properties.
For any form of cannabis, the most common risk is impaired memory and dependency. It is used both recreationally and for medical purposes, such as managing chronic pain, nausea, or certain neurological conditions. While some people view it as relatively low risk, marijuana can still affect memory, judgment, coordination, and mental health—especially with frequent or heavy use.
Follow the link to learn more on Marijuana.
A special section is made here for inhalants. Inhalants are not classified as such, but they produce mind-altering effects when people breathe their chemical vapours (inhaled). Unlike many other substances, inhalants are typically everyday household or industrial products not intended to be used as drugs.
Most inhalants cause a
Frequency of use may result in brain damage, even sudden death.
DrugAddiction.ca staff keep themselves up to date with current street drugs and other abused substances across the country to better help you navigate the subject with ease.
In the field of substance use and addiction, our experienced addiction consultants at DrugAddiction.ca regularly speak with families who are unsure what substance their loved one may be using. Through carefully guided conversations and targeted questions about behaviours, physical symptoms, and mood changes, our experts can often help identify the likely substance or category of drugs involved.
When one understands which substance may be contributing to the changes, it becomes much easier to recognize warning signs, assess the level of risk, and determine appropriate next steps. Clear, informed insight is often the first step toward effective support, early intervention, and meaningful recovery planning.
If you need help, please don’t hesitate to contact an expert at DrugAddiction.ca.
If you or someone you care about is struggling, you don’t need to navigate this alone. Free, confidential support is available every day.
