Final answer:
Using a pharmaceutical agent for something other than its intended use is called drug abuse. Drug abuse can lead to addiction, which is the compulsive use of a substance such as a psychoactive drug despite negative consequences. This addiction may produce physical or psychological dependence on the drug.
Step-by-step explanation:
Using a pharmaceutical agent for something other than its intended use is called drug abuse. It refers to the use of a drug without the advice of a medical professional and for reasons not originally intended. Drug abuse can lead to addiction, which is the compulsive use of a substance such as a psychoactive drug despite negative consequences. This addiction may produce physical or psychological dependence on the drug.