To understand why people use psychoactive drugs, we need to understand how they cause their powerful effects. We will now turn our attention to how drugs work in the brain.

Drugs can change a person's mood (e.g. causing euphoria), cognition (ability to think logically), level of consciousness (from very alert to very drowsy) and behaviour (act out of character). These effects are usually the reason people take the drug in the first place. The experience of ‘getting high’, ‘getting stoned’ or ‘tripping’ is caused by changes in the chemical systems of the brain.

Psychoactive drugs can act in several ways.

Before we look at these effects, let's talk about how the brain works without drugs.

A quick tour of the brain

The brain is our most complex organ and is the body's command centre. It is divided into different sections, or lobes, which focus on particular activities.

The occipital lobes, at the rear of the brain, are involved with vision. Parts of the temporal lobes, which are at the sides of the brain, process sound, and the parietal lobes, at the top of the brain, are largely responsible for integrating sensory information relating to taste and touch. Perhaps the most important are the frontal lobes, which, as the name suggests, are located at the front of the brain directly above our eyeballs.

The frontal lobes are responsible for, among other things, decision-making. This is where we balance the pros and cons of a particular action and decide if it is a good idea or not. None of the lobes work alone. Instead, they are joined by a complex network of nerves that reaches across the brain. This network helps the brain communicate information at high speed, making it very efficient.

How the brain ‘thinks’

The building blocks of this network are nerve cells called neurons. The adult human brain is thought to have between 80 and 100 billion of them. Neurons consist of a main cell body and a long, slender extension known as an axon (Fig. 4.1).