Drug Classifications: What do they mean

What is Australian Poison scheduling?

In Australia, the Therapeutic Goods Administration (TGA) manages a system called the Poisons Standard (also known as the SUSMP). This is essentially a giant library where every substance is placed on a specific shelf (known as a ‘Schedule’) based on how much professional supervision you need to use it safely.

The goal isn't to be restrictive for the sake of it; it’s to ensure that the riskier a substance is, the more a doctor or pharmacist will be involved in your care.

Drug schedules explained

Schedule 2 (Pharmacy Medicine)

Can be bought off the shelf, but only in a pharmacy. Example: basic hay fever tablets (antihistamines) or small packs of paracetamol and ibuprofen.

Schedule 3 (Pharmacist Only)

Aren't available on open shelves. You'll need to talk to the pharmacist directly so that they can check if the medicine is right for you. Example: a strong cold and flu tablet.

Schedule 4 (Prescription Only):

A script from a doctor is required. Example: blood pressure medications, most antidepressants, and antibiotics.

Schedule 8 (Controlled Drug)

The most strictly monitored due to a high risk of addiction or misuse but are required in medical contexts. Example: Strong painkillers like morphine, oxycodone or ADHD medications as well as drugs used for therapeutic purposes such as medical cannabis, and ketamine.

Schedule 9 (Prohibited Substances)

Illegal substances which have no currently approved medical use in a standard setting. Example: Cocaine, GHB, Heroin,Methamphetamine (ICE) or MDMA (unless for therapeutic use through the Authorised Prescriber Scheme).

The SUSMP and a list of all drug schedules is available online via the Federal Register of Legislation. Most everyday Australians will interact with Schedules 2, 3, 4, and 8.

Classifications by Physical Effect

When we move away from legal schedules and look at general classifications (used by the Alcohol and Drug Foundation) we’re often describing how drugs feel when they’re taken. Specifically, these classifications are describing how different drugs interact with your central nervous system, and how they affect the management of your brain receiving information and coordinates – this is what influences the activity of your body.

<h3> Cannabinoids

Cannabinoids are drugs that interact with your body’s endocannabinoid system (ECS). The ECS is a vital molecular network that regulates things like your mood, sleep, appetite, pain and immune response. This includes everything from the natural stuff found in the cannabis plant to synthetic versions made in a lab.

There are also cannabinoids that are naturally made in the body, which are known as endogenous ligands (or more commonly referred to as endocannabinoids).

Common cannabinoids include: Butane hash oil, Cannabis (THC), CBD (Cannabidiol), Medicinal cannabis, and Synthetic cannabinoids.

Depressants (Downers)

Depressants are substances that slow down your central nervous system, which is basically like tapping the brakes on the messages traveling between your brain and your body. This means that they will mess with your concentration, coordination, and how fast you can react to something unexpected (like while driving).

In small amounts, they can help you relax and feel a bit more at ease or lessen tension. In larger amounts, they can become more dangerous, and can lead to heavy drowsiness, vomiting, passing out, or even overdose.

Common depressants include: Alcohol, Benzodiazepines (Valium and Xanax), GHB and Kava.

Dissociatives

Dissociatives (also known as dissociative anaesthetics) are a type of psychedelic that can make you feel disconnected or detached from your own body or the world around you. Beyond that "out-of-body" sensation, they can also cause hallucinations and lead to shifts in how you think, feel, and experience reality.

Common dissociatives include: DXM (lean, dank), Ketamine, Nitrous oxide (nangs), and PCP (Phencyclidine).

Empathogens

Empathogens (also called entactogens) are substances that trigger a release of dopamine and serotonin in your brain. Since serotonin is responsible for managing your mood, sleep, and appetite, this rush can make you feel incredibly relaxed and happy.

However, once the effects wear off, your brain’s serotonin levels will drop and will often lead to mood swings, dehydration, and feelings of depression.

Common empathogens include: MDMA (Ecstasy), PMA and PMMA.

Psychedelics (or Hallucinogens)

Psychedelics (often called hallucinogens) are a type of substance that significantly shifts how you perceive the world, your mood, and the way you think. They affect all five of your senses, often warping your sense of time or causing deep emotional shifts. They can also lead to hallucinations where you might see or hear things that aren't there or distort your perception of the world around you.

Common psychedelics include: Ayahuasca, LSD, and Psilocybin (magic mushrooms).

Opioids

Opioids is a broad term for any drug that interact with the body’s opioid receptors. Natural opioids (known as opiates) are natural and come directly from the opium poppy plant rather than being created in a lab. Other categories are semi-synthetic opioids, which are created in labs through the chemical processing of opiates, and synthetic opioids, which are fully produced in labs with no opiates. Common opioids are:

• Opiates: Morphine and Codeine.
• Semi-synthetic opioids: Heroin and Oxycodone (Oxycontin and Percocet).
• Synthetic opioids: Fentanyl, Methadone and Tramadol.

All opioids are central nervous system depressants and will slow down the communication between your brain and the rest of your body.

Stimulants (Uppers)

Stimulants are drugs that kick the body into high gear by speeding up the signals between the brain and the rest of your central nervous system, making you feel more alert, energetic, and confident; However, they will often constrict blood vessels and increase your blood pressure resulting in an elevated heart rate. Stimulants fall into three main categories:

• Everyday Legals: Caffeine and nicotine.
• Prescriptions: Medications often used for focus or energy (such as Adderall, Ritalin or dexamphetamines).
• Illicit Drugs: Illegal substances (such as amphetamines, cocaine, speed, or meth / ice).

Is Mixing Different Drugs Harmful?

Understanding whether a substance is a stimulant or a depressant is vital because of how they interact. Mixing different classes of drugs, often called polysubstance use, significantly increases the risk of unpredictable physical and psychological reactions. When substances with opposing effects are combined, they create a complex mask that can hide dangerous levels of intoxication.

What Happens When You Mix Depressants with Depressants?

Depressants work by slowing down the central nervous system (CNS) by targeting different receptors in the brain. When mixed, the effects aren’t combined; they’re multiplied leading to a higher risk of overdose. The synergistic effect can quickly overload your body causing your vital functions to slow to a crawl or stop completely.

When mixing depressants, you’re suppressing the brain's ability to control basic survival functions, which can lead to respiratory depression (when the brain ‘forgets’ to tell the lungs to breathe), excessive sedation (falling into a heavy sleep and unable to wake up), aspiration (suppression of the gag reflex), and cardiovascular collapse (the heart rate and blood pressure severely drop leading to heart failure or coma).

For example, alcohol and benzodiazepines both affect GABA receptors, which can be considered the ‘brakes’ for the brain. When both are present in your system, the brakes are slammed to the floor, leading to a total shutdown of neural activity.

The Stimulant-Depressant Interaction

The combination of a stimulant (like caffeine or cocaine) and a depressant (like alcohol or opioids) creates a tug-of-war within the central nervous system. A particularly risky interaction because stimulants will often override the sedative cues of a depressant masking the overall effects. This can lead to you underestimating your level of impairment and continue drinking past the point of alcohol poisoning.

Cardiovascular Strain

Mixing stimulants (energy drinks) with depressants (alcohol) places significant strain on your cardiovascular system as your brain is receiving conflicting signals. Your heart is put under intense stress as it tries to reconcile the "speed up" messaging from the stimulant and the "slow down" messages from the depressant.

Risk of Delayed Overdose

Once the stimulant wears off, the full weight of the depressant can hit the system all at once, potentially leading to respiratory failure or loss of consciousness.

Depressants vs. Stimulants

If you’re looking for more information about alcohol and other drugs, you can visit our substance-specific drug information page.

Further Support and Information

If you or a loved one is struggling to navigate medications or substance use, please know that you don't have to figure it out alone. The Australian Drug Foundation offers educational materials to help you understand the complexities of substance use. Their resources cover a wide range of topics so that you can make informed decisions.

Otherwise, the best first port of call to understanding prescriptions is to talk directly to your GP or contact DirectLine, a confidential alcohol and drug counselling and referral service. If you're worried about an accidental overdose or a bad reaction to a substance you can call the Poisons Information Centre on 13 11 26.