So what do drugs do, how do they work….

When we talk about drugs, we are referring to ‘psychoactive’ drugs which is ‘a chemical entity used non-medically, self-administered for its psychoactive effect’ (WHO). When used, they alter a person’s mood, perception or brain function.

Our experience of a drug is influenced not only by the physiological effect of the drug on our body (usually the brain), but also by our expectations of the drug and the situation we use it in. The effects of the drug are thus not just the intrinsic property of the drug itself. Some drugs have several types of effects while others are unique in their properties. Some, like alcohol, can have a sedating effect on the brain function but this might be experienced in mood and behaviour as stimulating or disinhibiting.


We classify drugs according to their physiological effects and the effects they have on the Central Nervous System (CNS).

Watch the video for a good overview of this. 


Depressant Drugs don’t usually make a person feel depressed. Rather, they slow down (depress) the activity of the CNS and the messages going between the brain and the body. They affect someone’s concentration and coordination and slow down a person’s ability to respond to unexpected situations. In small quantities they can cause a person to feel more relaxed and less inhibited. In larger amounts they may cause things like drowsiness, vomiting, unconsciousness and death.

Depressant Drugs include alcohol, cannabis, heroin, benzodiazepines, GHB, opioids and inhalants.


Stimulant Drugs speed up the messages going between the brain and body. They can make a person feel more awake, alert, confident or energetic. Large quantities can “over-stimulate” a person, causing anxiety, panic, seizures, headaches, stomach cramps, aggression and paranoia. The effects can also be from using strong stimulants for a long period of time.

Stimulant drugs include caffeine, nicotine, methamphetamine, cocaine and ecstasy.


Hallucinogens distort a person’s perception of reality. People who take them may see or hear things that aren’t really there. Or what they see may be distorted in some way. The effects of hallucinogens vary greatly.

Hallucinogenic drugs include datura, ketamine, LSD, magic mushrooms, mescaline and PCP. Cannabis and ecstasy can also have hallucinogenic qualities.

How are drugs administered?

Once a drug has been administered, the human body uses the following mechanisms to deal wth it.

  • Adsorption (will depend on the route of administration)
  • Distribution (around the body and to the brain)
  • Metabolism (as the drug exerts its effect)
  • Excretion (out of the body)

How quickly and powerfully the effects are felt will depend on the route of administration (YSAS, 2001).

The various ways drugs can be administered are:

Oral Ingestion

This mode has the advantage of being non-invasive but the effectiveness of the drug is greatly reduced as it goes through the digestive tract. In the case of the stimulant drug cocaine, as much as 80% may be metabolised before reaching the receptor sites when ingested orally – therefore only 20% of the effects are felt. In view of the artificially inflated costs of illicit substances, young people will often seek routes of administration that offer better value for money. Consequently, the reduced effectiveness of a drug through oral administration is of great enough consequence to encourage the use of more high-risk routes such as injection (YSAS 2001).

Injection (Parenterally)

Drugs can be injected intravenously (via a vein), intramuscularly (via a muscle) or subcutaneously (under the skin) (NCETA 2004). Injection has the advantage of ensuring that a greater amount of the drug will arrive at the brains receptors in a shorter space of time. However injection drives a range of health harms specific to this route of administration including transmission of viral and bacterial diseases.

Insufflation (Sniffing or Snorting)

Insufflation refers to the sniffing or snorting of a drug. When drugs are self administered in this way, they are absorbed through the mucous membrane in the nose and into the blood stream.


Inhalation such as smoking cannabis or sniffing aerosols ensures blood from the lungs is pumped straight to the brain and the onset of drug action can often occur more rapidly than via intravenous injection.


Sublingual refers to placing a tablet (or wafer in the case of Suboxone) under the tongue where it is absorbed into the blood stream through the mucous membrane. Absorption is relatively rapid.


Transdermal modes of administration are those where the drug is absorbed through the skin, typically in ‘patch’ form (nicotine patches) or ointments.


Commonly referred to as ‘shelving’ or ‘shafting’ the drug is made into a suppository and inserted into the rectum and absorbed into the blood stream that way.

Learn more about Alcohol and other Drugs by choosing from the topics on the side-bar menu of this page.


Further Resources