Final answer:
Addiction is a disorder of the brain reward system characterized by the compulsive use of substances for immediate pleasure despite harmful consequences, often involving dopamine. Tolerance occurs when more substance is needed for the same effect, while withdrawal involves negative symptoms upon cessation.
Step-by-step explanation:
The disorder of the brain reward system that is characterized by repeatedly engaging in activities that bring about immediate pleasure is known as addiction. This condition involves the compulsive use of substances such as psychoactive drugs despite the negative consequences that the use may entail. The process of addiction is linked to the neurotransmitter dopamine, which is related to feelings of pleasure, motivation, and the reinforcement of behaviors that encourage its release. Drug addiction results from changes in brain chemistry and function, leading to the loss of control over drug intake and the desire to consume drugs despite adverse effects.
Tolerance is described as the phenomenon that occurs when a drug user requires more of a given drug to experience the same effects, indicating an adaptation to the substance. This is distinct from addiction but can be a component of the addiction process. On the other hand, withdrawal refers to the variety of negative symptoms experienced when drug use is discontinued, which often oppose the effects of the drug itself. Psychological dependence, or drug craving, is a significant aspect of addiction that involves a strong desire to use a substance to recreate the pleasure or avoid discomfort.