Your patient admits to using an illegal substance daily, thinking about it when not actually using it, and spending a lot of time figuring out where to get it. This patient could have:

A. Dementia: Dementia is a cognitive decline due to neurodegeneration, not compulsive drug use. B. A delusion: Delusions are false fixed beliefs not based in reality, unrelated to habitual substance use behavior. C. An addiction: Addiction involves compulsive substance use, preoccupation with the substance, and behavioral disruption due to its use. D. DTs: Delirium tremens is an acute withdrawal condition seen in alcohol dependence, not a description of ongoing drug-seeking behavior.