Final answer:
Addiction is a physical need for a substance that causes the brain's structure and function to change.
Step-by-step explanation:
Addiction is a physical need for a substance that causes the brain's structure and function to change. When someone becomes addicted to a substance, it means they have developed a dependence on it and experience withdrawal symptoms when they try to quit. This can result in changes in the brain's reward system and can lead to compulsive drug-seeking behavior.
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