Final answer:
Drug addiction is the compulsive use of drugs despite adverse consequences, and can lead to physical or psychological dependence. Drug abuse is using drugs without medical advice for off-label purposes, which can develop into addiction and increased tolerance.
Step-by-step explanation:
Drug addiction is defined as the compulsive use of a substance such as a psychoactive drug despite negative consequences that such use may entail. It involves a condition where continued use of a drug may lead to drug dependence, which can be either physical, characterized by withdrawal symptoms upon cessation, or psychological, indicated by drug craving. Rehabilitation from drug addiction usually includes psychotherapy and may also entail the use of other psychoactive drugs to manage withdrawal symptoms and cravings.
Drug abuse, on the other hand, refers to the use of a drug without the advice of a medical professional and for reasons not originally intended. Continued drug abuse can lead to addiction, with the user increasingly needing more of the drug to achieve the same effects—a condition known as tolerance. Tolerance can escalate to dangerous levels, potentially resulting in overdose and death.