The science of addiction
Addiction is a complex condition that affects how the brain processes reward, motivation and self-control. While substances such as alcohol or drugs can trigger addiction, behaviours — including gambling, gaming and excessive social media use — can activate the same brain circuits.
Models of addiction
Contemporary models of addiction utilise a neurobiological framework for the onset, development, and maintenance of an addiction. This approach defines addiction as a chronic and relapsing disorder marked by specific neuroadaptations predisposing an individual to pursue substances irrespective of potential consequences.
Pleasure — the good feeling we get from things like food, social connection, sex and certain drugs — is driven by chemical signals in the brain called neurotransmitters.
One of the most important of these chemicals is dopamine.
When dopamine is released in the brain’s reward system, it helps signal that something important or rewarding is happening. It shapes how strongly we experience reward, helps us learn what to expect from certain experiences, and motivates us to seek those experiences again.
All addictive drugs — despite acting on the brain in different ways — ultimately increase dopamine release in the brain’s reward system. This surge of dopamine strengthens the sense of reward and reinforces behaviours that lead to it.
Natural rewards such as food, sex and even activities like gambling can also trigger dopamine release. In contrast, when dopamine levels drop within these reward circuits, people may experience low mood, reduced motivation and a diminished ability to feel pleasure, symptoms often seen in depression or during drug withdrawal.
The dopamine reward cycle
Key brain regions involved include:
- the Ventral Tegmental Area, where dopamine-producing neurons originate
- the Nucleus Accumbens, which processes reward and motivation
- the Prefrontal Cortex, responsible for decision-making and impulse control
Together, these areas form the Mesolimbic Dopamine Pathway.
The addiction cycle
The neurobiological addiction cycle is commonly described in three repeating stages. Each stage reflects changes in brain systems involved in reward, stress and decision-making, and helps explain how occasional use or behaviour can develop into compulsive patterns over time.
The three stages of the addiction cycle are:
- Binge / Intoxication – when a substance or behaviour activates the brain’s reward system and produces pleasurable effects.
- Withdrawal / Negative Affect – when the rewarding effects fade and individuals may experience stress, discomfort, or low mood.
- Preoccupation / Anticipation – when cravings and thoughts about the substance or behaviour begin to dominate, often leading to relapse and restarting the cycle.
1. Binge/intoxication
In this stage, a substance or behaviour activates the brain’s reward system, producing pleasurable or reinforcing effects. These experiences are strongly linked to the release of Dopamine in the brain’s reward circuitry, including the Nucleus Accumbens. This surge signals that the experience is rewarding and worth repeating, strengthening the association between the behaviour and feelings of pleasure.
2. Withdrawal / Negative Affect
After the rewarding effects wear off, the brain may enter a state of stress or imbalance. People may experience irritability, anxiety, low mood or physical discomfort. These feelings are linked to changes in brain stress systems, including the Amygdala. At this stage, the behaviour may be repeated not only to seek pleasure, but also to relieve negative feelings.
3. Preoccupation / Anticipation
The final stage involves persistent cravings and an increased focus on obtaining the substance or engaging in the behaviour again. Changes in decision-making circuits, particularly in the Prefrontal Cortex, can reduce impulse control and make it harder to resist urges. This stage often drives relapse, restarting the cycle and reinforcing addictive patterns over time.
Explore QBI's addiction research
Podcast: The science of addiction
In this episode of A Grey Matter, we talked to QBI’s Dr James Kesby about the brain’s reward mechanism – the dopamine system – and how faults in this mechanism can cause disorders such as depression and addiction.
Why that cigarette, chocolate bar, or new handbag feels so good: how pleasure affects our brain
In this The Conversation article, QBI researcher, Dr James Kesby, explores how our ability to manage or maintain pursuits of pleasure often lie at the root of many neuropsychiatric disorders such as addiction and depression.