Introduction to biological explanations of drug addiction

Biological explanations focus on how changes in the body's internal processes, particularly in the brain, can lead to drug addiction. Drugs influence behaviour and mood by altering the levels of certain chemicals in the brain, which affects an individual's mood, behaviour, or overall mental state.

How drugs affect neurotransmitters and brain function

Drugs interfere with brain function by changing the availability of neurotransmitters, which in turn affects an individual's mood, behaviour, or overall mental state.

Key ways drugs impact neurotransmitters

• Brain adaptation - Over time, the brain adjusts to elevated neurotransmitter levels caused by drug use and begins to function as if they are normal. Without the drug, neurotransmitter levels drop too low, disrupting normal brain activity.
• Restoration through drug use - Taking the drug again restores these levels, allowing the brain to function properly once more. This creates a dependency where the person needs the drug just to feel normal.

This adaptation explains why stopping drug use suddenly can be difficult, as the brain struggles to cope without the artificial boost.

Dependence and withdrawal symptoms

Physical dependence occurs when the body becomes reliant on a drug to maintain normal functioning. This happens because the brain has adapted to the drug's effects on neurotransmitter levels.

The process of dependence

1. Initial drug use raises neurotransmitter levels, altering mood or behaviour.
2. The brain adapts to these elevated levels.
3. Without the drug, levels become too low, leading to impaired function.

Withdrawal symptoms

Withdrawal symptoms are unpleasant physical and psychological effects that occur when drug use stops. These arise as the brain tries to readjust to lower neurotransmitter levels.

Characteristics of withdrawal symptoms:

• Why they occur - The brain is compensating for the absence of the drug, which disrupts normal processes.
• Cycle of addiction - To relieve these symptoms, the individual often takes the drug again, reinforcing the dependence.

Reward deficiency syndrome as a biochemical explanation

Reward deficiency syndrome is a specific biochemical explanation for why some people become addicted to drugs. It centres on problems in the brain's dopamine system, which is responsible for feelings of pleasure and positive emotions.

Key features of reward deficiency syndrome

• Dopamine receptor deficiency - Some individuals have a genetic defect leading to fewer or less effective D₂ dopamine receptors.
• Inability to feel pleasure naturally - With fewer receptors, these people struggle to experience wellbeing from everyday activities, as their brains cannot process dopamine effectively.
• Self-medication with substances - To compensate, they may turn to drugs or substances that artificially increase dopamine levels, creating a sense of pleasure or relief. Common substances include alcohol and nicotine, which stimulate the dopamine system.

Tolerance and its role in addiction

Tolerance is a key aspect of addiction where the body becomes accustomed to a drug, requiring larger doses to achieve the same effects. This develops over time and contributes to escalating drug use.

Mechanisms of tolerance

• Reduction in receptor sites - Repeated drug use can decrease the number of receptor sites on the postsynaptic membrane.
• Decreased sensitivity - Alternatively, the existing receptor sites may become less responsive to the drug's chemical action.