Final answer:
Drug abuse is the use of a drug without medical advice and for unintended reasons, which can lead to drug addiction and dependence. Rehabilitation often involves psychotherapy and sometimes the use of other psychoactive drugs.
Step-by-step explanation:
Drug abuse is the use of a drug without the advice of a medical professional and for reasons not originally intended. Continued use of a psychoactive drug may lead to drug addiction, which is the compulsive use of a substance despite negative consequences. Drug addiction can result in physical or psychological dependence on the drug, and it may require rehabilitation involving psychotherapy and sometimes the temporary use of other psychoactive drugs.