How do drugs cause addiction?

Dopamine (DA) is a neurotransmitter released in the midbrain in response to a stimulus such as food or companionship (a “natural high”). Drugs indicated in causing dependence have been found to activate the reward pathway or mesolimbic dopaminergic pathway by acting on various brain regions in order to increase the extracellular dopamine level in the nucleus accumbens, therefore mimicking the “natural high” and “simply activating, or over activating, the body’s own pleasure system.”

 

Addiction is caused by chronic, unmanaged stress and the DA release triggered by repetitive drug use becomes a coping mechanism. The regulation of DA release in the midbrain becomes impaired, resulting in symptoms of diminished function, including loss of control, cravings and continued drug use-despite the knowledge of adverse consequences.

 

Recent research by Kent C. Berridge has led to the belief that the “pleasure-effect” of dopamine is more subtle than previously thought and that it contributes more to motivation. Therefore, drugs of abuse “flood” the brain with dopamine in the “wanting” regions which can trigger intense craving and makes the cells in these regions more sensitive to the drug following re-exposure; which can last for several years. Cravings for administration of the drug can continue even when pleasure is no longer derived.

 

For the individual mechanism of action of the drugs of abuse, please refer to the individual section.